Solar panel controller

On Wednesday, December 30, 2020 at 8:41:08 AM UTC-8, Eric Greenwell wrote:
Brian wrote on 12/30/2020 7:42 AM:
On Tuesday, December 29, 2020 at 8:42:19 AM UTC-7, krasw wrote:
Any ideas for Strobl controller replacement? The voltage is not enough for LFP battery. Victron SmartSolar MPPT 75/10 looks good, but according to specs Strobl solar cell voltage is not enough to start the unit (!). Genasun has appalling efficiency.

I put a 10 Watt a panel on my HP16. It averaged 200-250ma charging a 12AH Lead Acid batteries. The real advantage was when I was flying contests or safaris where I left the plane tied down. I could fly about 3 days in a row without needing to charge the battery. If we had a rest day it would pretty much top off the battery. I didn’t use a charge controller, I just used a volt meter. Since I only left it tied down when I was flying almost daily I didn’t figure 200-250 was enough to hurt the battery. But if I didn’t fly for more than a day I would disconnect it.

I loved having the solar panel, most of the time I didn’t need to charge the battery when flying daily. I wish I could come up with a reasonable panel to install on my LS6.

IMO Unless you are leaving the plane outside for extended periods without flying almost daily, my opinion is you don’t need a charge controller for a 20 watt or less solar panel. An appropriately sized and heat sinked Zenor diode would prevent it from overcharging if you did inadvertently leave it connected. If it is connected only when flying then no controller is required.

Brian's solution is a good one for gliders with a low enough current drain. Like Moshe, I
struggled to find a good place to put a useful amount of solar panel on my glider, given the
1.5 amp draw while flying. I eventually gave up trying, and installed a 20 AH Life battery,
which is enough capacity for two long flights. Normally, I recharge it after each flight from a
30 AH "donor" battery which is charged during the day by a 40W solar panel on the trailer,
using a DC-DC charger for electric model hobbyists. That's easy enough, and reliable.
--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

The problem with using the glider's solar panel to recharge the battery is that there is, simply, not enough sun hours available to do the job if you fly consecutive days. To recharge a 20AHr LFP with a 200mA panel will take 100 hr - and there is only about 7 sun hours available per day. Even a partial charge would take multiple days. I do exactly what Eric does except my battery charger is AC/DC so I can choose which power source I want to use. My preference is to use AC, but that may be inconvenient at some fields. My donor batteries total 40AHr, so I can go multiple days w/o recharging them.. My only glitch to date is one solar charge controller I bought from Bioenno literally melted when left out on the ramp (they replaced it under warranty).

Tom

On Tuesday, 29 December 2020 at 21:27:37 UTC+2, Eric Greenwell wrote:
krasw wrote on 12/29/2020 10:36 AM:
On Tuesday, 29 December 2020 at 18:52:35 UTC+2, jfitch wrote:
I'd be amazed if you had room for a Victron in your glider. Both Victron and Genasun make generally good stuff. From the data sheets, the Victron efficiency is "98% peak" and the Genasun is "94 - 99.85% typical". These are effectively the same. What do you find appalling?
On Tuesday, December 29, 2020 at 8:03:58 AM UTC-8, Soartech wrote:
On Tuesday, December 29, 2020 at 10:42:19 AM UTC-5, krasw wrote:
Any ideas for Strobl controller replacement? The voltage is not enough for LFP battery. Victron SmartSolar MPPT 75/10 looks good, but according to specs Strobl solar cell voltage is not enough to start the unit (!). Genasun has appalling efficiency.
We need more info: how many Volts does your cell put out? What is the battery type and size in Watt-hours? What aircraft is this on?

Genasun consumes 150mA, six times more than Victron (25 mA). My solar panel produces 550mA (via Strobl controller). Genasun robs almost third of the panel produced power.

The Genasum datasheet say 0.150 ma (150 ua), so much less power consumed than the Victron.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

Thanks, I should probably learn to read.

On Wednesday, 30 December 2020 at 01:58:04 UTC+2, Moshe Braner wrote:
I've often thought of adding small solar panels in my glider to extend
the battery life, but when I do the math it makes no sense. Most
gliders have very limited room for solar panels (unless you glue the
flexible type outside the cockpit). I am surprised you got 550 mA,
that's about 7 watts. But that's probably peak, when the panel is
perfectly aligned towards the sun, and not under a cloud, and the
average would be much lower, probably 200 mA or less. Meanwhile people
have been loading their gliders with so much electronics that they say
they need TWO 12AH batteries to last a flight. Let's take the example
of a 1-amp average load, i.e., one 12AH LFP battery (or two SLAs) would
last 12 hours. Add a 200mA-average solar charging setup and that
reduces the load on the battery to 0.8 amps, extending the battery life
to 15 hours. Useful?

I wouldn't bother with solar panels unless my glider was factory equipped with one. My panel draws 830mA and I have 2*7 Ah of battery capacity, but OTOH I like to have one fresh battery to extend my engine in those very cold days.

On 12/31/20 4:45 AM, krasw wrote:
On Wednesday, 30 December 2020 at 01:58:04 UTC+2, Moshe Braner wrote:
I've often thought of adding small solar panels in my glider to extend
the battery life, but when I do the math it makes no sense. Most
gliders have very limited room for solar panels (unless you glue the
flexible type outside the cockpit). I am surprised you got 550 mA,
that's about 7 watts. But that's probably peak, when the panel is
perfectly aligned towards the sun, and not under a cloud, and the
average would be much lower, probably 200 mA or less. Meanwhile people
have been loading their gliders with so much electronics that they say
they need TWO 12AH batteries to last a flight. Let's take the example
of a 1-amp average load, i.e., one 12AH LFP battery (or two SLAs) would
last 12 hours. Add a 200mA-average solar charging setup and that
reduces the load on the battery to 0.8 amps, extending the battery life
to 15 hours. Useful?

I wouldn't bother with solar panels unless my glider was factory equipped with one. My panel draws 830mA and I have 2*7 Ah of battery capacity, but OTOH I like to have one fresh battery to extend my engine in those very cold days.


Might want to be careful there. LFP's can be badly damaged when
charging under cold conditions.

On 12/31/2020 12:50 PM, kinsell wrote:

Might want to be careful there.Â* LFP's can be badly damaged when
charging under cold conditions.

Good point. "Cold" as in "below freezing" (0C, 32F) for charging, not
discharging. It seems like an arbitrary number (these batteries are not
made of water after all) but that's what they say. I'd recommend at
least several degrees above that for charging. If heading into the wave
with an LFP battery, if you have solar charging, you may want to
disconnect that (unless the charge controller does that automatically -
do the LFP-aware ones do that?). Would need a switch for that
disconnection. Otherwise it's another reason to avoid solar panels in
the glider, which can't help a lot with the battery running time anyway.

On Thursday, December 31, 2020 at 9:50:30 AM UTC-8, kinsell wrote:
On 12/31/20 4:45 AM, krasw wrote:
On Wednesday, 30 December 2020 at 01:58:04 UTC+2, Moshe Braner wrote:
I've often thought of adding small solar panels in my glider to extend
the battery life, but when I do the math it makes no sense. Most
gliders have very limited room for solar panels (unless you glue the
flexible type outside the cockpit). I am surprised you got 550 mA,
that's about 7 watts. But that's probably peak, when the panel is
perfectly aligned towards the sun, and not under a cloud, and the
average would be much lower, probably 200 mA or less. Meanwhile people
have been loading their gliders with so much electronics that they say
they need TWO 12AH batteries to last a flight. Let's take the example
of a 1-amp average load, i.e., one 12AH LFP battery (or two SLAs) would
last 12 hours. Add a 200mA-average solar charging setup and that
reduces the load on the battery to 0.8 amps, extending the battery life
to 15 hours. Useful?

I wouldn't bother with solar panels unless my glider was factory equipped with one. My panel draws 830mA and I have 2*7 Ah of battery capacity, but OTOH I like to have one fresh battery to extend my engine in those very cold days.

Might want to be careful there. LFP's can be badly damaged when
charging under cold conditions.

That is independent of whether or not a solar charge controller is used. You can always add a switch to disconnect it, or omit the solar panels altogether (which is what I did).

Tom

On Thursday, December 31, 2020 at 11:11:12 AM UTC-8, Moshe Braner wrote:
On 12/31/2020 12:50 PM, kinsell wrote:

Might want to be careful there. LFP's can be badly damaged when
charging under cold conditions.
Good point. "Cold" as in "below freezing" (0C, 32F) for charging, not
discharging. It seems like an arbitrary number (these batteries are not
made of water after all) but that's what they say. I'd recommend at
least several degrees above that for charging. If heading into the wave
with an LFP battery, if you have solar charging, you may want to
disconnect that (unless the charge controller does that automatically -
do the LFP-aware ones do that?). Would need a switch for that
disconnection. Otherwise it's another reason to avoid solar panels in
the glider, which can't help a lot with the battery running time anyway.

If you're airborne it doesn't matter because the output of the panel goes totally towards powering the avionics and no charging is happening.

Tom

Moshe Braner wrote on 12/31/2020 11:12 AM:
On 12/31/2020 12:50 PM, kinsell wrote:

Might want to be careful there.* LFP's can be badly damaged when charging under cold conditions.

Good point.* "Cold" as in "below freezing" (0C, 32F) for charging, not discharging.* It seems
like an arbitrary number (these batteries are not made of water after all) but that's what they
say.* I'd recommend at least several degrees above that for charging.* If heading into the wave
with an LFP battery, if you have solar charging, you may want to disconnect that (unless the
charge controller does that automatically - do the LFP-aware ones do that?).* Would need a
switch for that disconnection.* Otherwise it's another reason to avoid solar panels in the
glider, which can't help a lot with the battery running time anyway.

Do some LiFe batteries with a BMS stop charging at a low temperature? If so, maybe that's one
to put in the glider.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

Using the BMS to control charging is not considered good engineering practice. The BMS may or may not be designed to operate that way, but once it disconnects the power bus driven by the solar will be at uncontrolled and possibly damaging voltage. Also, different designs of BMS reset (and reconnect) in different ways, and maybe not how you expected.

On Thursday, December 31, 2020 at 3:25:05 PM UTC-8, Eric Greenwell wrote:
Moshe Braner wrote on 12/31/2020 11:12 AM:
On 12/31/2020 12:50 PM, kinsell wrote:

Might want to be careful there. LFP's can be badly damaged when charging under cold conditions.

Good point. "Cold" as in "below freezing" (0C, 32F) for charging, not discharging. It seems
like an arbitrary number (these batteries are not made of water after all) but that's what they
say. I'd recommend at least several degrees above that for charging. If heading into the wave
with an LFP battery, if you have solar charging, you may want to disconnect that (unless the
charge controller does that automatically - do the LFP-aware ones do that?). Would need a
switch for that disconnection. Otherwise it's another reason to avoid solar panels in the
glider, which can't help a lot with the battery running time anyway.
Do some LiFe batteries with a BMS stop charging at a low temperature? If so, maybe that's one
to put in the glider.
--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

On 12/31/20 12:12 PM, Moshe Braner wrote:
On 12/31/2020 12:50 PM, kinsell wrote:

Might want to be careful there.Â* LFP's can be badly damaged when
charging under cold conditions.

Good point.Â* "Cold" as in "below freezing" (0C, 32F) for charging, not
discharging.Â* It seems like an arbitrary number (these batteries are not
made of water after all) but that's what they say.Â* I'd recommend at
least several degrees above that for charging.Â* If heading into the wave
with an LFP battery, if you have solar charging, you may want to
disconnect that (unless the charge controller does that automatically -
do the LFP-aware ones do that?).Â* Would need a switch for that
disconnection.Â* Otherwise it's another reason to avoid solar panels in
the glider, which can't help a lot with the battery running time anyway.

I have a toggle switch to switch between my LiFePO4 in the baggage area
and my Pb battery in the tail. I have a separate switch to switch the
main battery and the aux battery. I flew around at 16 deg F for almost
4 hours and had no trouble with the batteries or the solar panels (5 of
them). Just because the OAT is below freezing does not mean the the
batteries are getting that cold in the cockpit. The tail battery,
however, could get pretty cold, but it's a Pb battery.

--
Dan
5J