Basic battery charging question

[[email protected]]

Can I charge 2 or more batteries simultaneously, connected in parallel?

(Assuming all batteries are the same type and approximately the same
age.)

-ted/2NO

[Paul Remde]

Hi Ted,

I don't recommend it. I am not an expert, but it is my understanding that
slight differences in the batteries will cause one to get much more of the
current than the other.

Good Soaring,

Paul Remde

> wrote in message
oups.com...
> Can I charge 2 or more batteries simultaneously, connected in parallel?
>
> (Assuming all batteries are the same type and approximately the same
> age.)
>
> -ted/2NO
>

[Andy]

How well it work will depend on the characteristics of the charger.
For a simple current limited, fixed voltage, charger they will both
reach full charge but probably not at the same time. If the charger
autoswitches to trickle mode when the first battery reaches the switch
over voltage it may take quite a bit longer, if ever, for the second
battery to get a full charge.

I think you'd be better off with separate chargers.

Andy

[Gary Evans]

On the DG800 there are 4 batteries that are charged
all at once in place. They are not designed to be removed
for spearate charging.

At 15:06 07 October 2005,
wrote:
>Can I charge 2 or more batteries simultaneously, connected
>in parallel?
>
>(Assuming all batteries are the same type and approximately
>the same
>age.)
>
>-ted/2NO
>
>

[01-- Zero One]

Ted,



If they are SLA (sealed lead acid) batteries like the typical ones we
use (12v 7AH) the answer is yes. Parallel batteries tend to charge and
discharge based on their individual capacities. Some of the battery
charger people even show this as a "standard" configuration when they
could easily insist on separate chargers for each battery.



A quick Google search will reveal a fair bit of 'wisdom' on this matter.



CAVEAT: Do not charge NiMH or other chemistry batteries in parallel.



Larry





" > wrote in message
oups.com:

> Can I charge 2 or more batteries simultaneously, connected in parallel?
>
> (Assuming all batteries are the same type and approximately the same
> age.)
>
> -ted/2NO

[Tim Mara]

no......not with a common "smart charger" we would typically use for glider
batteries......
First off, the charger should be matched to the battery (within reason) to
achieve a good charge.too small a charger outputs will not bring the battery
fully up to capacity, too large a charger will charge too quickly and
overcharge the battery which is also bad (or worse)
the Typical "smart" charger made for these "re-chargeable" batteries is
different than your standard motorcycle/auto battery charger and will
"sense" the condition of the battery and then charge in 2 or 3
modes....typically bulk, fill and maintenance (float).....if you have 2
batteries, the charger will sense the condition of one.or both.and charge
one.....or both as if it were the better.or worse..of the two since it will
be reading an overall condition......or the better.or the worse of the
two...maybe over-simplified....but I think this should give you some idea
tim
Wings & Wheels
www.wingsandwheels.com


> wrote in message
oups.com...
> Can I charge 2 or more batteries simultaneously, connected in parallel?
>
> (Assuming all batteries are the same type and approximately the same
> age.)
>
> -ted/2NO
>

[Gary Emerson]

Resist the temptation to try this in spite of the responses which indicate it's
ok IF you want to have batteries you can count on every time you soar.

Some of the manufacturers do make tail batteries or other onboard battery packs
which are 2-6 individual cells wired up in parallel. Although it may work, it's
an example of poor electrical engineering.




wrote:

> Can I charge 2 or more batteries simultaneously, connected in parallel?
>
> (Assuming all batteries are the same type and approximately the same
> age.)
>
> -ted/2NO
>

[Andy]

Not sure what you mean by a 6 volt cell so assume you mean a 6 volt
battery. The 2 individual 6 volt batteries are probably wired in
series which is perfectly good engineering. In fact that configuration
has a significant advantage over a single 12 volt battery. That is
that the batteries can be linked by a fuse that is, in effect, internal
to the battery and protects it from terminal shorts. I used that
configuration for years.

2 6 volt batteries in series will behave like one 12 volt battery as
far as charging is concerned. Only the packaging is different.

If you really meant parallel perhaps you could describe the
configuration in a bit more detail.

Andy

[Eric Greenwell]

wrote:

> Can I charge 2 or more batteries simultaneously, connected in parallel?
>
> (Assuming all batteries are the same type and approximately the same
> age.)

What situation prompted you to ask this question? A better answer can be
provided with that knowlege.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

[[email protected]]

Eric:

My glider uses three 12V 7 amp/hr batteries. At least two, and usually
all three, have to be recharged after every flight. (One of the three
operates the transponder alone.) I often don't have the time to charge
each battery one at a time between flights on consecutive days. (And at
contests I will have 6, if not 9, batteries!) I wanted to find out if I
can charge them three at a time before I invested in two more chargers.

-ted/2NO

[[email protected]]

I would only charge SLA batteries in parallel if they were also
discharged in parallel. Otherwise you run the risk of substantial
currents flowing from the battery with a higher to charge to the other.
You could use 3 lamp timers so you didn't have to attend the things.

Tom Seim
2D DG-400

[Eric Greenwell]

wrote:

> I would only charge SLA batteries in parallel if they were also
> discharged in parallel. Otherwise you run the risk of substantial
> currents flowing from the battery with a higher to charge to the other.
> You could use 3 lamp timers so you didn't have to attend the things.

Prudence suggests following Tom's advice to use a charger for each
battery. If you use chargers that switch to float voltage automatically,
you won't need the timers. Besides being faster chargers that will make
your batteries last longer, they are simpler to use: connect and forget.

A clever person could use a single charger with 3 diodes in the output,
so the charge would be delivered to the lowest battery first. If the
charger sufficient amp output to replace all the combined amphours
needed by the three batteries in a day, and the charger was adjusted to
compensate for the diode voltage drop, that might also be satisfactory.
With as many batteries as you have, I still think buying two more
chargers would be the way to go!

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

[Gary Emerson]

two to six individual 12v batteries all in parallel

Andy wrote:

> Not sure what you mean by a 6 volt cell so assume you mean a 6 volt
> battery. The 2 individual 6 volt batteries are probably wired in
> series which is perfectly good engineering. In fact that configuration
> has a significant advantage over a single 12 volt battery. That is
> that the batteries can be linked by a fuse that is, in effect, internal
> to the battery and protects it from terminal shorts. I used that
> configuration for years.
>
> 2 6 volt batteries in series will behave like one 12 volt battery as
> far as charging is concerned. Only the packaging is different.
>
> If you really meant parallel perhaps you could describe the
> configuration in a bit more detail.
>
> Andy
>

[[email protected]]

Ack! Thanks everyone. Very informative.

Now if I can figure out why my water pump slows from 2 gallons a minute
on startup to a quarter gallon a minute a short time later ...

~ted/2NO

[David Kinsell]

wrote:
> Ack! Thanks everyone. Very informative.

Don't feel too grateful, most of the information was bunk,
this being RAS and all.

There's no big damaging currents involved, that's a myth that's
been perpetrated over the years by people who don't understand
battery charging. See it for yourself, take a charged and
discharged battery and hook them together through an ammeter.
Two similar SLA batteries have almost no capability for
cross-charging.

About the only relevant comment was that a charger intended for
overnight charging might not get the job done in a reasonable
amount of time, with multiple discharged batteries. It won't
shorten the life of the batteries, it just might not meet your
needs. I'd favor individual chargers, mainly because the charge
lights would give a little more information on the state of
individual batteries. But either way could work.

A little surprised about your need to carry nine batteries around.
I know people flying with 12 volts tend to use more batteries, but
nine seems like some kind of modern record. Maybe if you got the
voltage right, that nine wouldn't actually be needed? Oh heck, that's
probably a whole different discussion. Let's save that for next
week.



> Now if I can figure out why my water pump slows from 2 gallons a minute
> on startup to a quarter gallon a minute a short time later ...
>
> ~ted/2NO
>

A 12 volt battery on a 14 volt pump?? :-)

-Dave

[Mike the Strike]

1..2..3..4..5..6..7..8..9..10......

OK, three batteries is quite normal in modern sailplanes. My
arrangement is exactly the same as Ted's - one dedicated to the
transponder, and two for the instruments. The spare for the
instruments is just in case you run out of juice (I run mine for two
days or up to 10 hours before recharge) as well as loss of primary
source through blown fuse, disconnected wire, etc.) My new spare sits
in the fin where it doubles as ballast.

Many of us also carry spares at contests so you can swap a used battery
for a freshly charged one.

But maybe we agree on one thing - nine is perhaps a bit over the top!

Mike

[[email protected]]

David Kinsell wrote:
> wrote:
> > Ack! Thanks everyone. Very informative.
>
> Don't feel too grateful, most of the information was bunk,
> this being RAS and all.
>
> There's no big damaging currents involved, that's a myth that's
> been perpetrated over the years by people who don't understand
> battery charging. See it for yourself, take a charged and
> discharged battery and hook them together through an ammeter.
> Two similar SLA batteries have almost no capability for
> cross-charging.
>
> About the only relevant comment was that a charger intended for
> overnight charging might not get the job done in a reasonable
> amount of time, with multiple discharged batteries. It won't
> shorten the life of the batteries, it just might not meet your
> needs. I'd favor individual chargers, mainly because the charge
> lights would give a little more information on the state of
> individual batteries. But either way could work.
>
> A little surprised about your need to carry nine batteries around.
> I know people flying with 12 volts tend to use more batteries, but
> nine seems like some kind of modern record. Maybe if you got the
> voltage right, that nine wouldn't actually be needed? Oh heck, that's
> probably a whole different discussion. Let's save that for next
> week.
>
>
>
> > Now if I can figure out why my water pump slows from 2 gallons a minute
> > on startup to a quarter gallon a minute a short time later ...
> >
> > ~ted/2NO
> >
>
> A 12 volt battery on a 14 volt pump?? :-)
>
> -Dave

Hey Dave, have you bothered to read the SLA battery data sheets? I
doubt it. Power Sonic's indicate the internal resistance at 7 mohm.
That's milli ohms, as in one one thousands of an ohm. Now if you have a
one volt difference with 7x2 mohm you get about 70A of current. Don't
bother trying to measure this with a DVM, it will equalize much too
fast for the meter to register it. You will need a scope with a current
probe or shunt to see it (and you will need to know how to set up the
scope for one shot transient digitizing, assuming it is a digital
scope). Is this going to damage the batteries? Maybe, maybe not. But I
don't recommend it. You could eliminate the issue by using some series
resistors, say 1 ohm, that wouldn't effect the charging, but limit the
cross currents to acceptable levels.

Tom Seim
2G DG400

[Andy]

He could also try connecting the charged and discharged batteries with
a 1 amp fast blow fuse. Repeat until convinced or batteries
equalized.

Andy

[David Kinsell]

wrote:
> David Kinsell wrote:
>> wrote:
>>> Ack! Thanks everyone. Very informative.
>> Don't feel too grateful, most of the information was bunk,
>> this being RAS and all.
>>
>> There's no big damaging currents involved, that's a myth that's
>> been perpetrated over the years by people who don't understand
>> battery charging. See it for yourself, take a charged and
>> discharged battery and hook them together through an ammeter.
>> Two similar SLA batteries have almost no capability for
>> cross-charging.
>>
>> About the only relevant comment was that a charger intended for
>> overnight charging might not get the job done in a reasonable
>> amount of time, with multiple discharged batteries. It won't
>> shorten the life of the batteries, it just might not meet your
>> needs. I'd favor individual chargers, mainly because the charge
>> lights would give a little more information on the state of
>> individual batteries. But either way could work.
>>
>> A little surprised about your need to carry nine batteries around.
>> I know people flying with 12 volts tend to use more batteries, but
>> nine seems like some kind of modern record. Maybe if you got the
>> voltage right, that nine wouldn't actually be needed? Oh heck, that's
>> probably a whole different discussion. Let's save that for next
>> week.
>>
>>
>>
>>> Now if I can figure out why my water pump slows from 2 gallons a minute
>>> on startup to a quarter gallon a minute a short time later ...
>>>
>>> ~ted/2NO
>>>
>> A 12 volt battery on a 14 volt pump?? :-)
>>
>> -Dave
>
> Hey Dave, have you bothered to read the SLA battery data sheets? I
> doubt it. Power Sonic's indicate the internal resistance at 7 mohm.
> That's milli ohms, as in one one thousands of an ohm. Now if you have a
> one volt difference with 7x2 mohm you get about 70A of current.

Yes, I'm quite familiar with battery data sheets, thank you. The low
values quoted are the resistance of the internal lead conductors.

> Don't
> bother trying to measure this with a DVM, it will equalize much too
> fast for the meter to register it.

It will equalize way too fast?? So you're saying that maybe 3 A-H of
charge gets transferred in what, less than .1 second?? It's physically
impossible to actually charge or discharge a battery that fast, but it
is fascinating to consider the currents required. 3 A-H in a generous
..1 second would be, let's see here, 3 * 60 * 60 / .1, or something over
100,000 AMPS. And you wouldn't even notice this on the display?? I
think there'd be only a smoking hole in the table where the ammeter
used to sit, if something like this were possible.



> You will need a scope with a current
> probe or shunt to see it (and you will need to know how to set up the
> scope for one shot transient digitizing, assuming it is a digital
> scope).

I can tell from this you've never actually done it, since what you'd
see on the scope is nothing. The batteries don't cross-charge, they
just sit there. Which is why a car or airplane has their regulator
set to 14.5 volts, not 12 or 12.8. Which, of course, is why all
aircraft radios are designed to the higher voltage.

To charge a battery, you have to raise the terminal voltage by about
1.5 volts to even get a trickle charge. You're reversing a chemical
reaction internally, which takes a different voltage compared to
discharging.

You can see this by connecting a trickle charger, which shows the
immediate bump. By your calculations, this would take about 200
amps, which you may not realize, isn't actually being supplied
by a typical 300 ma trickle charger.



> Is this going to damage the batteries? Maybe, maybe not. But I
> don't recommend it. You could eliminate the issue by using some series
> resistors, say 1 ohm, that wouldn't effect the charging, but limit the
> cross currents to acceptable levels.
>
> Tom Seim
> 2G DG400
>


The fact that nobody else realized the problems with this posting
really reinforces my statement that the average glider pilot seems
to be rather naive about some fundamental electrical concepts. That's
fine, just wish they didn't keep posting hogwash as authoritative
information.

-Dave

[David Kinsell]

Mike the Strike wrote:
> 1..2..3..4..5..6..7..8..9..10......
>
> OK, three batteries is quite normal in modern sailplanes. My
> arrangement is exactly the same as Ted's - one dedicated to the
> transponder, and two for the instruments. The spare for the
> instruments is just in case you run out of juice (I run mine for two
> days or up to 10 hours before recharge)

Haven't "lost juice" in 20 years, so maybe it's a low risk, if you
have the right battery.


> as well as loss of primary
> source through blown fuse, disconnected wire, etc.)

Again, could happen, but not in 20 years for me.


> My new spare sits
> in the fin where it doubles as ballast.
>
> Many of us also carry spares at contests so you can swap a used battery
> for a freshly charged one.

Going to a camp, I do carry two batteries, in case one get dropped or
a wire breaks on the flight line or something. Or maybe a cell starts
to go bad, and I see that in flight. Of course, a cell could go totally
dead and still would have enough juice for multiple additional flights.
It's like carrying the spare in one more cell, rather than in an
additional battery.

>
> But maybe we agree on one thing - nine is perhaps a bit over the top!
>
> Mike
>

It does seem a bit excessive. Wonder how many car batteries he carries
around with him?

-Dave

[Eric Greenwell]

David Kinsell wrote:

> wrote:
>
>> Ack! Thanks everyone. Very informative.
>
>
> Don't feel too grateful, most of the information was bunk,
> this being RAS and all.
>
> There's no big damaging currents involved, that's a myth that's
> been perpetrated over the years by people who don't understand
> battery charging. See it for yourself, take a charged and
> discharged battery and hook them together through an ammeter.
> Two similar SLA batteries have almost no capability for
> cross-charging.

I tried this with a couple batteries no longer used in my glider. As
long as one of them wasn't completely discharged, the currents involved
were within the normal charging rates initially, then tapered off
quickly. A battery discharged to 9 volts connected to a fully charged
one did have current 2.5 times the normal maximum charging rate until my
wimpy clip leads started to smoke (experiment terminated). Since that is
a unlikely situation, charging 2 or 3 similar batteries in parallel
isn't a problem in that regard.

>
> About the only relevant comment was that a charger intended for
> overnight charging might not get the job done in a reasonable
> amount of time, with multiple discharged batteries. It won't
> shorten the life of the batteries, it just might not meet your
> needs. I'd favor individual chargers, mainly because the charge
> lights would give a little more information on the state of
> individual batteries.

This seems the best reason for individual chargers, and it would allow
picking the best charger for the battery. A charger for several parallel
batteries would be more of a compromise.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

[[email protected]]

David Kinsell wrote:
> wrote:
> > David Kinsell wrote:
> >> wrote:
> >>> Ack! Thanks everyone. Very informative.
> >> Don't feel too grateful, most of the information was bunk,
> >> this being RAS and all.
> >>
> >> There's no big damaging currents involved, that's a myth that's
> >> been perpetrated over the years by people who don't understand
> >> battery charging. See it for yourself, take a charged and
> >> discharged battery and hook them together through an ammeter.
> >> Two similar SLA batteries have almost no capability for
> >> cross-charging.
> >>
> >> About the only relevant comment was that a charger intended for
> >> overnight charging might not get the job done in a reasonable
> >> amount of time, with multiple discharged batteries. It won't
> >> shorten the life of the batteries, it just might not meet your
> >> needs. I'd favor individual chargers, mainly because the charge
> >> lights would give a little more information on the state of
> >> individual batteries. But either way could work.
> >>
> >> A little surprised about your need to carry nine batteries around.
> >> I know people flying with 12 volts tend to use more batteries, but
> >> nine seems like some kind of modern record. Maybe if you got the
> >> voltage right, that nine wouldn't actually be needed? Oh heck, that's
> >> probably a whole different discussion. Let's save that for next
> >> week.
> >>
> >>
> >>
> >>> Now if I can figure out why my water pump slows from 2 gallons a minute
> >>> on startup to a quarter gallon a minute a short time later ...
> >>>
> >>> ~ted/2NO
> >>>
> >> A 12 volt battery on a 14 volt pump?? :-)
> >>
> >> -Dave
> >
> > Hey Dave, have you bothered to read the SLA battery data sheets? I
> > doubt it. Power Sonic's indicate the internal resistance at 7 mohm.
> > That's milli ohms, as in one one thousands of an ohm. Now if you have a
> > one volt difference with 7x2 mohm you get about 70A of current.
>
> Yes, I'm quite familiar with battery data sheets, thank you. The low
> values quoted are the resistance of the internal lead conductors.
>

You better go back and read the data sheet again. The internal
resistance specified is for the entire battery delivering current to a
load. You can measure it yourself by using two different valued load
resistors and a DVM to measure the delta battery voltage. The internal
resistance for charging will be different that discharging, and is not
specified because they expect you to current limit the charging
current. Obviously, if you parallel two batteries with different charge
states you WILL get cross charging that WILL NOT be current limited.
This is BAD!

> > Don't
> > bother trying to measure this with a DVM, it will equalize much too
> > fast for the meter to register it.
>
> It will equalize way too fast?? So you're saying that maybe 3 A-H of
> charge gets transferred in what, less than .1 second?? It's physically
> impossible to actually charge or discharge a battery that fast, but it
> is fascinating to consider the currents required. 3 A-H in a generous
> .1 second would be, let's see here, 3 * 60 * 60 / .1, or something over
> 100,000 AMPS. And you wouldn't even notice this on the display?? I
> think there'd be only a smoking hole in the table where the ammeter
> used to sit, if something like this were possible.

Who knows? Who CARES?!! Don't DO IT! IT IS BAD FOR BOTH BATTERIES!!!


>
> The fact that nobody else realized the problems with this posting
> really reinforces my statement that the average glider pilot seems
> to be rather naive about some fundamental electrical concepts. That's
> fine, just wish they didn't keep posting hogwash as authoritative
> information.
>

What I posted about using two current limiting resistors WILL WORK and
WILL PREVENT HARM TO THE BATTERIES without affecting the charging. I am
an electrical engineer that has been doing circuit design - including
battery powered circuitry - for over 30 years.

Tom Seim
2G DG400
Richland, WA

[P. Corbett]

Eric Greenwell wrote:
> wrote:
>
>> Can I charge 2 or more batteries simultaneously, connected in parallel?
>>
>> (Assuming all batteries are the same type and approximately the same
>> age.)
>
>
> What situation prompted you to ask this question? A better answer can be
> provided with that knowlege.
>
>
I know that this is an old thread but I thought that I would pose this
question. First some history: the longest lasting glider battery that I
ever had was 6 years and I only replaced it because I believed that it
HAD to quit any minute due to its age. It was a 14 volt SLA that I built
from two 2.0 volt 4AH batteries in parallel and one 7AH battery in
series with the pair. The charger was a 12 volt gel cell charger. I
never charged for a period longer than overnight. Now the question...is
it possible that undercharging e.g. charging a 14 volt battery with a 12
volt charger is responsible for the longevity of the battery? BTW, I
built another, same way, 4 years ago and it is doing fine.

Paul

[Eric Greenwell]

P. Corbett wrote:
> Eric Greenwell wrote:
>> wrote:
>>
>>> Can I charge 2 or more batteries simultaneously, connected in parallel?
>>>
>>> (Assuming all batteries are the same type and approximately the same
>>> age.)
>>
>>
>> What situation prompted you to ask this question? A better answer can
>> be provided with that knowlege.
>>
>>
> I know that this is an old thread but I thought that I would pose this
> question. First some history: the longest lasting glider battery that I
> ever had was 6 years and I only replaced it because I believed that it
> HAD to quit any minute due to its age. It was a 14 volt SLA that I built
> from two 2.0 volt 4AH batteries in parallel and one 7AH battery in
> series with the pair. The charger was a 12 volt gel cell charger. I
> never charged for a period longer than overnight. Now the question...is
> it possible that undercharging e.g. charging a 14 volt battery with a 12
> volt charger is responsible for the longevity of the battery? BTW, I
> built another, same way, 4 years ago and it is doing fine.

Generally, undercharging lead acid batteries leads to shorter life, not
longer. Six years is not uncommon for a SLA battery, though it's
capacity will be diminished. If it's reduced capacity was still adequate
for your flights, you wouldn't know how good it was unless you tested it
for it's actual capacity.

Now, I have to ask: why are you using a 14 volt battery? If it's for
your radio, what radio do you have? You may not need 14 volts at all.

--
Change "netto" to "net" to email me directly

Eric Greenwell - Washington State, USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
Operation"

[P. Corbett]

Eric Greenwell wrote:
> P. Corbett wrote:
>
>> Eric Greenwell wrote:
>>
>>> wrote:
>>>
>>>> Can I charge 2 or more batteries simultaneously, connected in parallel?
>>>>
>>>> (Assuming all batteries are the same type and approximately the same
>>>> age.)
>>>
>>>
>>>
>>> What situation prompted you to ask this question? A better answer can
>>> be provided with that knowlege.
>>>
>>>
>> I know that this is an old thread but I thought that I would pose this
>> question. First some history: the longest lasting glider battery that
>> I ever had was 6 years and I only replaced it because I believed that
>> it HAD to quit any minute due to its age. It was a 14 volt SLA that I
>> built from two 2.0 volt 4AH batteries in parallel and one 7AH battery
>> in series with the pair. The charger was a 12 volt gel cell charger. I
>> never charged for a period longer than overnight. Now the
>> question...is it possible that undercharging e.g. charging a 14 volt
>> battery with a 12 volt charger is responsible for the longevity of the
>> battery? BTW, I built another, same way, 4 years ago and it is doing
>> fine.
>
>
> Generally, undercharging lead acid batteries leads to shorter life, not
> longer. Six years is not uncommon for a SLA battery, though it's
> capacity will be diminished. If it's reduced capacity was still adequate
> for your flights, you wouldn't know how good it was unless you tested it
> for it's actual capacity.
>
> Now, I have to ask: why are you using a 14 volt battery? If it's for
> your radio, what radio do you have? You may not need 14 volts at all.
>
Eric

I have a Terra 720 and the manual states that the radio wants 13.75 VDC.
Ironically, I don't talk on the radio much because the many
conversations going on are distracting to me so I leave it off most of
the time. On a typical flight, it sees a 25% duty cycle. But if I need
it, I want it to work well, thus the 14 VDC. Overkill? What do you think?

Paul

[Mike]

These battery threads are almost as entertaining as the PW 6/2-33
threads. How about addressing the "memory" issue? Myth or reality?
Thank god the season is upon us here in the NE USA. I'm looking forward
to trying out my newly purchased gizmos (PDA GPS etc). I just hope the
batteries work.

Mike

[Eric Greenwell]

P. Corbett wrote:
> Eric Greenwell wrote:
>>
>> Now, I have to ask: why are you using a 14 volt battery? If it's for
>> your radio, what radio do you have? You may not need 14 volts at all.
>>
> Eric
>
> I have a Terra 720 and the manual states that the radio wants 13.75 VDC.
> Ironically, I don't talk on the radio much because the many
> conversations going on are distracting to me so I leave it off most of
> the time. On a typical flight, it sees a 25% duty cycle. But if I need
> it, I want it to work well, thus the 14 VDC. Overkill? What do you think?
>
> Paul

That radio is old enough that 14 volts might be a reasonable strategy.
The TPX 720 handheld I'm familiar with works well on 12 volts, but I
don't know if that would apply to the panel mount 720.

Maybe some pilots out there have experience with a 720 on 12 volts and
can tell us how well it worked.

--
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Eric Greenwell - Washington State, USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
Operation"

[Don Byrer]

>> I have a Terra 720 and the manual states that the radio wants 13.75 VDC.
>> Ironically, I don't talk on the radio much because the many
>> conversations going on are distracting to me so I leave it off most of
>> the time. On a typical flight, it sees a 25% duty cycle. But if I need
>> it, I want it to work well, thus the 14 VDC. Overkill? What do you think?

"14 volt" aircraft have a 12 volt battery. The alternator makes ~14V
(nominal 13.8V); the alternator voltage must be higher than battery
voltage for the battery to charge. Methinks the radio should work
acceptably on 12V, probably even 11-ish...but I do not have
experience with the Terra 720.

--Don



Don Byrer
Commercial Pilot / CFI Student
Electronics Technician, RADAR/Data/Comm @ CLE
Amateur Radio KJ5KB

"I have slipped the surly bonds of earth; now if I can just land without bending the gear..."
"I know what it sounds like....when doves cry" (Bird Strike 8/29/05)

[Doug]

I have the 720A and find it very sensitive to voltage. We run ours using a
12v battery and have no problem as long as the voltage stays above the
11.2-12v range. When the voltage does drop much below 11.2 the radio starts
sounding bad to others.

A weak, older battery will give you nothing but headaches with this radio.

Doug

"Don Byrer" > wrote in message
...
>
>
>>> I have a Terra 720 and the manual states that the radio wants 13.75 VDC.
>>> Ironically, I don't talk on the radio much because the many
>>> conversations going on are distracting to me so I leave it off most of
>>> the time. On a typical flight, it sees a 25% duty cycle. But if I need
>>> it, I want it to work well, thus the 14 VDC. Overkill? What do you
>>> think?
>
> "14 volt" aircraft have a 12 volt battery. The alternator makes ~14V
> (nominal 13.8V); the alternator voltage must be higher than battery
> voltage for the battery to charge. Methinks the radio should work
> acceptably on 12V, probably even 11-ish...but I do not have
> experience with the Terra 720.
>
> --Don
>
>
>
> Don Byrer
> Commercial Pilot / CFI Student
> Electronics Technician, RADAR/Data/Comm @ CLE
> Amateur Radio KJ5KB
>
> "I have slipped the surly bonds of earth; now if I can just land without
> bending the gear..."
> "I know what it sounds like....when doves cry" (Bird Strike 8/29/05)