battery charger to get through Piper power port?

David Lesher writes:

I don't suggest this lightly, knowing the BS and $$, but have you
considered adding a 2nd jack, smaller in size? That COULD be fused
at say 60A, and live. That could accommodate both a charger, or your
power-tug, with no risk to your aluminum friend...or you while in it.

Standing at the plane a few nights ago, I considered the same thing.
I've been working on blending a small charger and some old batteries
(from my electric lawn mower) to make a compatible charger.

I decided that I should add some resistance just in case one of the
batteries (plane or charger) gets really low. I don't want a sudden
rush through it. Then I realized that if I'm going to do that I might
as well just use small connectors and wire. And if I'm going to do
that I don't really need to use the high-power port.

However...using the existing power port is handy. The best thing about
it is that it's externally accessible. I can put a charger on it
without leaving the nose open. I leave expensive stuff (headsets) in
the nose so even in my (shared) hangar it's worthwhile to keep it
locked, but it's especially advantageous if I'm on the ramp somewhere
leaving the cabin and engine and heaters on.

Perhaps the answer is to bridge the relay contacts with a low-current
toggle circuit breaker? That would allow me to easily control whether
or not trickle charging or discharge can occur through the port but if
I happen to leave it enabled and a short or reverse polarity condition
occurs the circuit would be broken.

See any problems with that?

Thank you.

--kyler

Kyler Laird writes:

I don't suggest this lightly, knowing the BS and $$, but have you
considered adding a 2nd jack, smaller in size? That COULD be fused
at say 60A, and live. That could accommodate both a charger, or your
power-tug, with no risk to your aluminum friend...or you while in it.

Standing at the plane a few nights ago, I considered the same thing.
I've been working on blending a small charger and some old batteries
(from my electric lawn mower) to make a compatible charger.

What you want is a trickle charger; it need furnish only say 100mA
or so. (This assumes you religiously plug it in while hangared, of
course. Same scheme as most firetrucks.) A common source is the
residential alarm industry; they use a small PCB with a regulator
and a wallwart transformer. {I'll give you one if you need it.....just
to do it safely..}

I decided that I should add some resistance just in case one of the
.....
Good!

However...using the existing power port is handy.

My point was: "using AN external port is handy.."

Perhaps the answer is to bridge the relay contacts with a low-current
toggle circuit breaker? That would allow me to easily control whether
or not trickle charging or discharge can occur through the port but if
I happen to leave it enabled and a short or reverse polarity condition
occurs the circuit would be broken.

If you do that; the "ground power" contactor will close and stay closed;
costing you your protection. Hmm, you'd need a SPDT switch I think but
I'd want to draw it out. Not undoable, and perhaps cheaper than a 2nd
hole in the skin, etc.
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

: I decided that I should add some resistance just in case one of the
: batteries (plane or charger) gets really low. I don't want a sudden
: rush through it. Then I realized that if I'm going to do that I might
: as well just use small connectors and wire. And if I'm going to do
: that I don't really need to use the high-power port.

I would think a circuit breaker would be a better idea than a resistor. If
you go through the trouble of making a well-thought-out bypass for the interlocking
mechanism, why limit yourself to a trickle charge?

: Perhaps the answer is to bridge the relay contacts with a low-current
: toggle circuit breaker? That would allow me to easily control whether
: or not trickle charging or discharge can occur through the port but if
: I happen to leave it enabled and a short or reverse polarity condition
: occurs the circuit would be broken.

I think that this could be done well, but I would try to add some interlocking
to the bypass. Probably some diode logic to the coil of a relay. Then you could
protect yourself from reverse polarity on the plug, and overcurrent protect the large
solenoid bypass. Without schematics I can't say for sure the best way, but as I said
before, I'd try to think of every possible failure mode. I'm sure that Piper did.

Along the same lines, I've notice a significant difference in the later
PA-28's from my '69 model. Mine has a 60A breaker in the ALT feed line and the later
ones don't. All I can say is if mine ever tripped, it could put a big load dump
transient on the bus. That could cook a lot of avionics in a hurry.

Be careful,

-Cory


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

writes:

: I decided that I should add some resistance just in case one of the
: batteries (plane or charger) gets really low. I don't want a sudden
: rush through it. Then I realized that if I'm going to do that I might
: as well just use small connectors and wire. And if I'm going to do
: that I don't really need to use the high-power port.

I would think a circuit breaker would be a better idea than a resistor.

I really would want a current limiter (not a current killer) in that
situation. I'd still want to charge the battery just not so quickly.

If
you go through the trouble of making a well-thought-out bypass for the interlocking
mechanism, why limit yourself to a trickle charge?

It's all that I need. I have no need for a fast charge and by keeping
it slow I can use the low-power bypass circuit.

: Perhaps the answer is to bridge the relay contacts with a low-current
: toggle circuit breaker? That would allow me to easily control whether
: or not trickle charging or discharge can occur through the port but if
: I happen to leave it enabled and a short or reverse polarity condition
: occurs the circuit would be broken.

I think that this could be done well, but I would try to add some interlocking
to the bypass. Probably some diode logic to the coil of a relay. Then you could
protect yourself from reverse polarity on the plug, and overcurrent protect the large
solenoid bypass.

The circuit breaker should do that. I'm thinking of isolating it from the
relay with diodes but I'm waiting to find my schematics before figuring
out exactly how to do that.

--kyler

What you need is a REGULATED lab power supply that has adjustable
voltage and current adjustments. I use a 0 to 33 volt at 0 to 30
amp power supply that has digital readouts for voltage and current
that I bought surplus.
Set the charge voltage and max charge current and plug it in. As the
battery charges the supply will switch from current limit mode to
voltage limit mode automatically.

You cannot feed the power into the APU port for a long time (more than
10 minutes) or it will generally fry the APU port relay because most
are not rated for continuous operation.
Install a charging jack on an inspection panel and wire it direct to
the battery with a FUSE at the battery that will support the expected
charging current from your power supply.
For 12v systems set the power supply to 14.00 to charge overnight or
13.45 for long term float charge. Double these voltages for a 24 volt
system. These voltages need to be adjusted some what if the
temperature is not close to 70F. This voltage verses temperature data
can be found on the internet for the type of battery you are using.

You do NOT want to use a low cost common UNREGULATED trickle charger
or you will surely fry your expensive battery by over charging.
Don't take the battery caps off unless you intend to charge at very
high rates or the acid will cover everything near the battery.
John

On Thu, 17 Mar 2005 15:08:05 GMT, Kyler Laird
wrote:

David Lesher writes:

I don't suggest this lightly, knowing the BS and $$, but have you
considered adding a 2nd jack, smaller in size? That COULD be fused
at say 60A, and live. That could accommodate both a charger, or your
power-tug, with no risk to your aluminum friend...or you while in it.

Standing at the plane a few nights ago, I considered the same thing.
I've been working on blending a small charger and some old batteries
(from my electric lawn mower) to make a compatible charger.

I decided that I should add some resistance just in case one of the
batteries (plane or charger) gets really low. I don't want a sudden
rush through it. Then I realized that if I'm going to do that I might
as well just use small connectors and wire. And if I'm going to do
that I don't really need to use the high-power port.

However...using the existing power port is handy. The best thing about
it is that it's externally accessible. I can put a charger on it
without leaving the nose open. I leave expensive stuff (headsets) in
the nose so even in my (shared) hangar it's worthwhile to keep it
locked, but it's especially advantageous if I'm on the ramp somewhere
leaving the cabin and engine and heaters on.

Perhaps the answer is to bridge the relay contacts with a low-current
toggle circuit breaker? That would allow me to easily control whether
or not trickle charging or discharge can occur through the port but if
I happen to leave it enabled and a short or reverse polarity condition
occurs the circuit would be broken.

See any problems with that?

Thank you.

--kyler

John_F wrote:
: For 12v systems set the power supply to 14.00 to charge overnight or
: 13.45 for long term float charge. Double these voltages for a 24 volt
: system. These voltages need to be adjusted some what if the
: temperature is not close to 70F. This voltage verses temperature data
: can be found on the internet for the type of battery you are using.

You may want slightly higher voltages than that. From what I've read, and
from working on a hybrid electric car with lead-acid batteries (granted, they were
SLA, not FLA), you can alegedly float them at 13.8 indefinately without damage. As
for an overnight, 14.0 probably won't give quite an equalization charge on the cells.
It may bubble a little bit, but 14.5 will probably help rejuvenate the cells more than
14... again, *only* for an overnight charge... not indefinately.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

(John_F) writes:

What you need is a REGULATED lab power supply that has adjustable
voltage and current adjustments. I use a 0 to 33 volt at 0 to 30
amp power supply that has digital readouts for voltage and current
that I bought surplus.

The last thing a pilot wants in a hangar is a lab-grade supply. They don't
tolerate abuse well...

The regulator-modules I referred to, such as
http://homesecuritystore.com/ezStore123/DTProductZoom.asp?productID=1037
or many other units, produced regulated 13.8v/etc to charge the
battery. I'd not worry too much about current limiting; the wallwart
powering it helps there..and the regulator will as well. (The units
typically produce an amp or two at best; & with most wallwarts, far
less....)


You cannot feed the power into the APU port for a long time (more than
10 minutes) or it will generally fry the APU port relay because most
are not rated for continuous operation.

True! That's another reason I did not suggest such. It's a Bad Idea.

Install a charging jack on an inspection panel and wire it direct to
the battery with a FUSE at the battery that will support the expected
charging current from your power supply.

This is an approach as well. But the OP likely wanted to avoid drilling
more holes in his aircraft....I wonder why?

These voltages need to be adjusted some what if the
temperature is not close to 70F. This voltage verses temperature data
can be found on the internet for the type of battery you are using.

True, but you can just err on the low side; you do NOT want to
overcharge the battery. Note the alternator does not know the battery
temperature, either.


--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

Kyler:

However...using the existing power port is handy. The best thing about
it is that it's externally accessible.


A downside is the size and $$$ of the mating connectors.

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433