Solar Battery Tender 24v

[gevertex]

Hey All,

  I am thinking about either buying or building a solar battery tender. Mine will be tied down outside with covers as hangar space is unobtainium at the moment. Anyone have any sources for parts or a full system I could use? I have done some research, but it's not obvious what I need given it's 24v.

This will be used on a Concorde battery as soon as it's in stock / ships (probably Dec/Jan)

Edited November 13, 2022 by gevertex

[A64Pilot]

Military has used them in their 24V trucks for a long time, so they do exist.

Just be sure their output voltage is controlled, for the 24V Concorde pretty sure the float voltage is 26.4V, twice the 13.2 float voltage for their 12V battery.

I think I might buy an adjustable PWM controller and panel separately, small quality PWM controllers are widely available and inexpensive, MPPT controllers are more efficient, but you don’t need that for a maintainer. Maybe a flexible panel Velcroed to the cover? Velcro because they aren’t real flexible

Many cheap solar battery maintainers don’t control voltage very well, they count on the output being so small, but can over time cook a battery.

[gevertex]

23 hours ago, A64Pilot said:

Military has used them in their 24V trucks for a long time, so they do exist.

Just be sure their output voltage is controlled, for the 24V Concorde pretty sure the float voltage is 26.4V, twice the 13.2 float voltage for their 12V battery.

I think I might buy an adjustable PWM controller and panel separately, small quality PWM controllers are widely available and inexpensive, MPPT controllers are more efficient, but you don’t need that for a maintainer. Maybe a flexible panel Velcroed to the cover? Velcro because they aren’t real flexible

Many cheap solar battery maintainers don’t control voltage very well, they count on the output being so small, but can over time cook a battery.

All of the charge controllers I see are 27.6v float.  Any particular source for one with the correct voltage?

[A64Pilot]

1 hour ago, gevertex said:

All of the charge controllers I see are 27.6v float.  Any particular source for one with the correct voltage?

I’d contact Concorde to be sure what the proper float voltage is, I’m using 13.2V from Concorde’s Lifeline batteries which are I’m told pretty much identical.

99% sure that an AGM’s float voltage is lower than a flooded battery and a just generic float charger is flooded voltage.

Just looked Trojan flooded float voltage is 13.5V for a 12V battery.

My best guess is to buy a good adjustable PWM controller and connect it to the panel of your choice, I think good small quality programmable PWM controllers like a Renogy is well less than $50, and program it to the voltage you want.

‘This one maybe? Haven’t read it’s specs but as long as it’s voltage can be programmed it ought to work, but there are others of course

https://www.amazon.com/Renogy-Wanderer-Amp-12V-24V/dp/B07NPDWZJ7/ref=sr_1_4?crid=JS7ZLU0XTAR2&keywords=renogy%2Bvoyager%2B20a%2B12v%2F24v%2Bpwm%2Bwaterproof%2Bsolar%2Bcharge%2Bcontroller&qid=1668477487&sprefix=solar%2Bpwm%2Bcontroller%2B24v%2Caps%2C221&sr=8-4&th=1

Or Concorde may know a supplier, can’t hurt to call and ask. They are good, helpful people.

Concorde is a smallish US family owned business, no multi nationals or Chineses here, if you look at the Company phone tree you’ll see I believe Godfrey a lot, that’s the family name that started the company in the 70’s. But if you call you’ll get someone in the Company who knows what they are talking about, unless things have changed.

[carusoam]

Inviting @OSUAV8TER…

He has an interesting engineering team that has designed a really nice aircraft pre-heat system…

This solar battery maintainer idea… might be interesting to that team…

Best regards,

-a-

[gevertex]

1 hour ago, A64Pilot said:

I’d contact Concorde to be sure what the proper float voltage is, I’m using 13.2V from Concorde’s Lifeline batteries which are I’m told pretty much identical.

99% sure that an AGM’s float voltage is lower than a flooded battery and a just generic float charger is flooded voltage.

Just looked Trojan flooded float voltage is 13.5V for a 12V battery.

My best guess is to buy a good adjustable PWM controller and connect it to the panel of your choice, I think good small quality programmable PWM controllers like a Renogy is well less than $50, and program it to the voltage you want.

‘This one maybe? Haven’t read it’s specs but as long as it’s voltage can be programmed it ought to work, but there are others of course

https://www.amazon.com/Renogy-Wanderer-Amp-12V-24V/dp/B07NPDWZJ7/ref=sr_1_4?crid=JS7ZLU0XTAR2&keywords=renogy%2Bvoyager%2B20a%2B12v%2F24v%2Bpwm%2Bwaterproof%2Bsolar%2Bcharge%2Bcontroller&qid=1668477487&sprefix=solar%2Bpwm%2Bcontroller%2B24v%2Caps%2C221&sr=8-4&th=1

Or Concorde may know a supplier, can’t hurt to call and ask. They are good, helpful people.

Concorde is a smallish US family owned business, no multi nationals or Chineses here, if you look at the Company phone tree you’ll see I believe Godfrey a lot, that’s the family name that started the company in the 70’s. But if you call you’ll get someone in the Company who knows what they are talking about, unless things have changed.

Apparently the voltages for GA batteries are different than automotive batteries of the same type due to differences in the specific gravity of the electrolyte. It's supposedly aviation specific to give the batter better energy density. So, if I could adjust the voltage then that might work.  As I understand it though, these controllers are designed to charge a battery for use with another load for the purposes of providing stable power via solar. I am not sure the voltage would be adjustable as it's an integrated charge circuit not just a fixed voltage? Maybe I am wrong there?

https://www.batteryminders.com/why-an-aviation-specific-charger-maintainer/

[gevertex]

56 minutes ago, carusoam said:

Inviting @OSUAV8TER…

He has an interesting engineering team that has designed a really nice aircraft pre-heat system…

This solar battery maintainer idea… might be interesting to that team…

Best regards,

-a-

I have seen at least one person with one next to their plane. I'll have to get mine back from maintenance before that will be useful to me. Possibly this week.

[N201MKTurbo]

They aren’t hard to find.

https://www.amazon.com/s?k=24+volt+solar+battery+charger&gclid=EAIaIQobChMI_7zMjqKv-wIVvhKtBh13dQpJEAAYASAAEgLk5PD_BwE&hvadid=176943843731&hvdev=c&hvlocphy=9030089&hvnetw=g&hvqmt=e&hvrand=3704199109942003103&hvtargid=kwd-5222237735&hydadcr=7806_9761249&tag=googhydr-20&ref=pd_sl_5xaqy3j21k_e

 

https://www.pulsetech.net/catalog/product/view/id/15119/s/sp-24-6-pulsetech-24v-battery-solar-pulse-charger-maintainer-6w/category/4718/
 

 

[N201MKTurbo]

BTW, the best way to maintain your battery is to use it on a regular basis. 

[A64Pilot]

10 hours ago, gevertex said:

Apparently the voltages for GA batteries are different than automotive batteries of the same type due to differences in the specific gravity of the electrolyte. It's supposedly aviation specific to give the batter better energy density. So, if I could adjust the voltage then that might work.  As I understand it though, these controllers are designed to charge a battery for use with another load for the purposes of providing stable power via solar. I am not sure the voltage would be adjustable as it's an integrated charge circuit not just a fixed voltage? Maybe I am wrong there?

https://www.batteryminders.com/why-an-aviation-specific-charger-maintainer/

Flooded aviation batteries do in fact contain stronger acid than automotive batteries, this is done to get more power from a lighter battery. Place I worked at years ago ruined a bunch of batteries by saving money and buying automotive battery acid locally to place the new Gill aircraft batteries in service.

However I’m 90% sure that’s not true on Concordes batteries, but again a call would settle everything. 

Usually better controllers have three stage charging, and sometimes equalization, this is because they are meant to recharge a battery that’s cycled daily, however that’s not what we are after here, we only want to maintain, not re-charge, so we want to lock in float voltage.

Every better controller I’ve been around has the capability to lock in one voltage and skip the stages, often this is labeled a Lithium setting as you don’t charge Lithium batteries in different voltage stages like lead acid.

Then there is the thought that little panels can’t hurt a battery because they simply don’t have enough current to raise the voltage high enough to do harm, and it’s a valid point, but they also in most cases won’t keep a battery at 100% SOC either, but they are better than nothing.

Like everything it all depends on how perfect a system your after, a tiny little panel even if it outputs 30V would work because it would never reach that voltage, just doesn’t make enough amps to drive the voltage up that high, but it wouldn’t be “perfect” that’s holding exact float voltage.

You should be able to buy a 50W flexible good quality Solar panel for $100 or less and a controller for certainly less than $50, so $150 all in, and I bet that’s a high estimate. I’d look for an outdoor / waterproof controller.

I’ve not looked into it, and a controller can increase or decrease voltage, but I think I’d look at running two 25W 12V panels in series instead of a single 50W to increase the voltage. The little panels I think are often lower as in 12V panels, but will output 18 to 20V I think, I have no little panel experience.

I had 250W panels on my boat and their voltage was about 30 I think, the Outback 80 MPPT controller of course decreased the voltage to charge the 12V battery bank. 

[A64Pilot]

Oh, unfortunately “pulse” charging to de-sulphate a battery etc is snake oil, I wished it worked, but it doesn’t. Only way to partially de-sulphate a battery is an equalization charge which is an intentional supervised overcharge, Concorde has a different name for it, forget what they call it, equalization has been around for a looong time, it’s nothing new.

Batteries sulphate faster when left at a partial charge over time, that’s what maintainers prevent of course, they maintain 100% SOC and slow sulphation as much as possible and can add years to the life of a battery.

All your looking for in a maintainer is that it holds the correct precise float voltage for your battery, voltage does vary by battery type and manufacturer, so a Gill and a Concorde will require a different maintainer, or an adjustable one.

I’m a big believer in maintainers, I have 5 plugged in right now

[Pinecone]

53 minutes ago, A64Pilot said:

Every better controller I’ve been around has the capability to lock in one voltage and skip the stages, often this is labeled a Lithium setting as you don’t charge Lithium batteries in different voltage stages like lead acid.

You also don't charge lithium batteries at a single voltage.  Unless you like fires.

Lithium batteries are charged in two stages.  The first stage is a Constant Current phase.  The voltage is adjusted to maintain the desired current, based on the battery capacity.  For long life, you want to charge at a 1C rate.  That is a 16 amp hour battery, would be charged at 16 amps. 

This current is maintained until the voltage reaches a specific voltage, then you switch to the Constant Voltage phase.  For a lithium polymer battery (like cell phones, tablets, and RC models), that voltage is 4.2 volts per cell.  At that cross over point, the battery is about 80% charged.  For longer life, many devices only charge to this level.

If you want a true full charge, you hold the voltage at that level until the charge current drops to near 0.

If you apply 4.2 volts per cell to a discharged battery, you will most likely overheat it from an extremely high current, and it will, as described in the industry, "vent with flames." 

 

A good adjustable power supply can do this charge cycle with one setup.  You set max current to the rate you want for the CC phase, and the max voltage to the CV phe voltage, and the power supply holds both to their limits.

[A64Pilot]

Solar chargers almost always don’t have the amperage to charge anywhere near 1C, charging from completely dead to 100% SOC at 1C would take 1 hour, Solar chargers almost always if properly sized can’t go from depleted to full in a complete Solar day, ideally you size your bank to use 1/3 rated capacity daily for a long life and to get you through the cloudy days and you size Solar to replace that 1/3 daily. So there just isn’t anywhere near the amperage available to cook off a battery, but any decent charger can be set to limit current of course

But that’s neither here or there, we are talking about floating a Lead Acid battery, and many chargers have a “lithium” mode that locks the charger to one voltage, which is what you want to do. A lead acid battery is self regulating, if voltage is correct it will only accept the correct charge current regardless of how many amps the charger is capable of producing, lead acid is simple, one reason they are still around

But it doesn’t matter, if you can get 1/2 amp or so set to float voltage, you have accomplished the mission in this case. 1/2 amp at 26V is roughly 14W, maybe 16 as there are losses of course, 16W isn’t too hard to get from 50W of panels, even on an overcast day, heck 50W is probably overkill, half that’s probably good enough.

Only point is that for maybe $100 or so if you desired you can easily put together a Solar battery tender for your 24V aircraft battery.

Is it worth it? Who knows, maybe, but aircraft have sat on ramps for a long time without them, depends I guess if you like to tinker and enjoy projects.

[gevertex]

On 11/15/2022 at 1:05 PM, A64Pilot said:

Solar chargers almost always don’t have the amperage to charge anywhere near 1C, charging from completely dead to 100% SOC at 1C would take 1 hour, Solar chargers almost always if properly sized can’t go from depleted to full in a complete Solar day, ideally you size your bank to use 1/3 rated capacity daily for a long life and to get you through the cloudy days and you size Solar to replace that 1/3 daily. So there just isn’t anywhere near the amperage available to cook off a battery, but any decent charger can be set to limit current of course

But that’s neither here or there, we are talking about floating a Lead Acid battery, and many chargers have a “lithium” mode that locks the charger to one voltage, which is what you want to do. A lead acid battery is self regulating, if voltage is correct it will only accept the correct charge current regardless of how many amps the charger is capable of producing, lead acid is simple, one reason they are still around

But it doesn’t matter, if you can get 1/2 amp or so set to float voltage, you have accomplished the mission in this case. 1/2 amp at 26V is roughly 14W, maybe 16 as there are losses of course, 16W isn’t too hard to get from 50W of panels, even on an overcast day, heck 50W is probably overkill, half that’s probably good enough.

Only point is that for maybe $100 or so if you desired you can easily put together a Solar battery tender for your 24V aircraft battery.

Is it worth it? Who knows, maybe, but aircraft have sat on ramps for a long time without them, depends I guess if you like to tinker and enjoy projects.

So you wouldn't mind say a 29v float voltage even if  the battery really required only 27v? I get what you are saying about charge current (limited current would drop the voltage IIRC). But say you had a week of clear summer days. Seems like 50W would be enough to over charge the battery even during 1 day of that. These batteries are only ~300Wh. Just 6 hours to go from flat to full. It also appears temperature is a factor. See Concorde's recommended voltage regulator setting.



Link:

https://batterymanagement.concordebattery.com/BatteryDocs/5-0324-rg-manual.pdf

 

So maybe I set the charge controller to 28v (a good middle ground). I can do that using the lithium mode of a solar charge controller? Or is it in multiples of 3.7v?

Edited November 21, 2022 by gevertex

[A64Pilot]

I do t think you understand, no I’m not abdicating over float voltage for a maintainer

But the fact exists that many cheap products could under ideal circumstances get there, and one could argue that they do work, because the incidence of overcharging is extremely small, because they are so low power. I bet the majority of the less expensive cheap chargers fall into this category. However ensuring they don’t overcharge by keeping output so low also guarantees you don’t ever maintain 100% SOC either, so in my opinion they are junk, but they are out there.

You often see them with cigarette lighter plugs, idea is to put one on the dash of your car while you leave it at the airport for extended times etc

Almost all legacy chargers did supply insane voltage, if left on a battery long enough they would hit quite high voltages and overcharge a battery.

But it’s not the 1970’s anymore, it’s the 21st Century and for very little money you can buy a Solar controller that will maintain voltage to .1V or better

Yes if you got an actual 50W you could likely cook a battery in a short time IF the voltage wasn’t tightly controlled, 50W at 14V is 3.5 Amps, maintainers are often much smaller, just to maintain you only really need 1/4 amp or so, just enough to overcome parasitic loads and self discharge rate, but that occurs 24/7 and Solar you only get about 4 hours a day from flat panels, better of course if they are properly oriented, but sitting on an airplane cover they won’t be, so maybe you need 2 or 3 amps maybe for four hours

A 50W panel isn’t small, a hard panel is about 2Ft x 1.5Ft and a flexible panel is likely even larger, but you don’t get 50W, your doing good to get half that for a couple hours a day, even less for the rest of the day.

So those little 6 inch things that you put on your dash? I don’t know, but would guess 5W or less.

So what I am abdicating is instead of buying overpriced, possibly junk, is to put something together yourself with an adjustable quality controller that you can be sure holds exactly the correct voltage, and ideally have a big enough panel so that even on less than perfect days it has enough output to maintain float voltage.

Or to say the heck with it, nobody else on the ramp is doing it and so long as they fly regularly they don’t have any problems.

But some of us like to tinker

[gevertex]

32 minutes ago, A64Pilot said:

I do t think you understand, no I’m not abdicating over float voltage for a maintainer

But the fact exists that many cheap products could under ideal circumstances get there, and one could argue that they do work, because the incidence of overcharging is extremely small, because they are so low power. I bet the majority of the less expensive cheap chargers fall into this category. However ensuring they don’t overcharge by keeping output so low also guarantees you don’t ever maintain 100% SOC either, so in my opinion they are junk, but they are out there.

You often see them with cigarette lighter plugs, idea is to put one on the dash of your car while you leave it at the airport for extended times etc

Almost all legacy chargers did supply insane voltage, if left on a battery long enough they would hit quite high voltages and overcharge a battery.

But it’s not the 1970’s anymore, it’s the 21st Century and for very little money you can buy a Solar controller that will maintain voltage to .1V or better

Yes if you got an actual 50W you could likely cook a battery in a short time IF the voltage wasn’t tightly controlled, 50W at 14V is 3.5 Amps, maintainers are often much smaller, just to maintain you only really need 1/4 amp or so, just enough to overcome parasitic loads and self discharge rate, but that occurs 24/7 and Solar you only get about 4 hours a day from flat panels, better of course if they are properly oriented, but sitting on an airplane cover they won’t be, so maybe you need 2 or 3 amps maybe for four hours

A 50W panel isn’t small, a hard panel is about 2Ft x 1.5Ft and a flexible panel is likely even larger, but you don’t get 50W, your doing good to get half that for a couple hours a day, even less for the rest of the day.

So those little 6 inch things that you put on your dash? I don’t know, but would guess 5W or less.

So what I am abdicating is instead of buying overpriced, possibly junk, is to put something together yourself with an adjustable quality controller that you can be sure holds exactly the correct voltage, and ideally have a big enough panel so that even on less than perfect days it has enough output to maintain float voltage.

Or to say the heck with it, nobody else on the ramp is doing it and so long as they fly regularly they don’t have any problems.

But some of us like to tinker

I like to tinker also, just trying to learn from your experiences. I generally like the approach of a smaller panel if I can set the maximum voltage precisely. Perhaps you are right. Flying more often is the best antidote to a rundown battery.  Maybe I'll buy a few parts to experiment with.

[A64Pilot]

Panel size doesn’t have anything to do with voltage, except that if the panel can’t supply enough current, then it can’t raise the battery voltage to the set point assuming you have a controller. Ideally your panels are bigger than min that way they can always supply the current and the excess capacity is just wasted as it’s not used so long as there is a controller

This is common with ALL chargers, example you have a dead battery, and connect your 12 Amp 110V charger to charge it up, you will notice at first the voltage is rather low, at this stage we are what’s called current limited because if it were available the battery could accept more than 12 Amps, then after time we hit the voltage set point, and after that voltage remains constant but the current is decreasing, we are now in absorption AKA voltage limited, eventually a quality charger will drop to float voltage.

Ideally that’s based on a programmable current set point, usually about .5% of the rated capacity of the battery, so for a 100AH battery it will drop to float when the current has dropped to 1/2 amp, but that’s only good high buck chargers, almost all drop to float at a set time, and almost always to prevent overcharging it does so before the battery is fully charged. Charging does continue at float voltage, but it does so at a painfully slow rate.

Some simply connect a small panel directly to a battery and get away with it if the panel is small enough, because the voltage output of a “12V” panel is actually around 17V, if the panel is small enough they get away with it, the cigarette lighter panels you put on your dash for example, because the panel is just too small to drive the voltage up.

Lead acid batteries are pretty tough and accept abuse well, for example float in a 12V one may be 13.2, but the whole time we drive around in our cars or fly our airplanes we are throwing 14 V at it, essentially absorption voltage, yet they do just fine with the overcharge, even the vehicles that may drive 8 hours a day or more.