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Solar trickle charge electrickery question


ThePog
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A quick question.

My truck is 24v and as I have not used it much I am seeing some parasitic drain on the batteries. 

I have been thinking about a solar trickle charger, basically because I can use it on anything 24v.

However if I buy this unit with dual outputs;

"12/24V 10A Dual Battery PWM Solar Charge Controller with LED Indicator | Jaycar Electronics New Zealand" https://www.jaycar.co.nz/12-24v-10a-dual-battery-pwm-solar-charge-controller-with-led-indicator/p/MP3760

I could potentially charge 24v or 12v batteries. 

So the question is; If I get a panel suitable for 12v charging, could I hook the outputs to each 12v battery in my system and charge them at 12v without disconnecting the batteries from each other? Obviously there will be a 12v potential between the two but will the charger care?

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Hey mate the way I read that is-

That charger needs the batteries separated for it to work eg: you could put an isolation switch in your link between your 2x 12v batteries then yes it'll charge them independently, but you would then need to disconnect your charger when you go back to 24v re-closing your link. 

It will try to balance both batteries to the same voltage but depending on your batteries internal resistance they will need different charging rates to achieve this, Eg one might charge at 3amps the other at 4 for 6 hours to reach 14volts or fully charged. 

*My explanation may be way off btw* more technical people can confirm or deny this.

 

 

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18 minutes ago, Muncie said:

Hey mate the way I read that is-

That charger needs the batteries separated for it to work eg: you could put an isolation switch in your link between your 2x 12v batteries then yes it'll charge them independently, but you would then need to disconnect your charger when you go back to 24v re-closing your link. 

It will try to balance both batteries to the same voltage but depending on your batteries internal resistance they will need different charging rates to achieve this, Eg one might charge at 3amps the other at 4 for 6 hours to reach 14volts or fully charged. 

*My explanation may be way off btw* more technical people can confirm or deny this.

Yea I imagined they would need to be separated but this would mean reprogramming the stupid stereo every time.

Thinking about it now, if they were not disconnected from each other the higher potential battery would be feeding the lower potential one in addition to the charging so probably would mess things up.

I have found this unit which might be the go;

https://hardkorr.com/nz/product-category/solar-panels/trickle-chargers/

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Nope battery’s in series for 24 volt don’t equalise between themselves 

can charge one or the other while connected to vehicle easy as on solar as long as you don’t muck polarity up - 

matched solar 12v on each battery would be best or switch one between as needed  

charging rates may be different but that’s what the regulator is for 

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6 minutes ago, Transom said:

Nope battery’s in series for 24 volt don’t equalise between themselves 

can charge one or the other while connected to vehicle easy as on solar as long as you don’t muck polarity up - 

matched solar 12v on each battery would be best or switch one between as needed  

charging rates may be different but that’s what the regulator is for 

 

1 minute ago, h4nd said:

Or just have 2x 12V cells and trickle chargers, one on each battery? Job done. 

If you really only want 1x 12V solar cell, use an isolated dc-dc power supply for the 2nd trickle charger and battery, https://www.aliexpress.com/item/1005002553820256.html

(There will of course be some inefficiency say 5% to 15% depending...)

Right. But i would still have to disconnect the two batteries otherwise the battery not being charged will drag it up/down?

I am guessing a series 24v setup will never charge correctly on the alternator, so a 24v charger will be no worse...?

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9 minutes ago, ThePog said:

Right. But i would still have to disconnect the two batteries otherwise the battery not being charged will drag it up/down?

Nope, no need to disconnect. in either case (2x solar and charger, OR one solar, one isolator, 2x charger), each battery will get charged to it's correct voltage, regardless of if it needs e.g. 2A or 2.2A trickle. Same as using 2x 12V mains battery chargers - As long as at least one charger isn't ground referenced, all good!

(keep the 2x solar cells isolated if you choose that, they'll be 12V apart. No sharing ground wires, etc).

12 minutes ago, ThePog said:

I am guessing a series 24v setup will never charge correctly on the alternator, so a 24v charger will be no worse...?

24V from Alt may not perfectly balance, but (isolated) 2x 12v means each battery will eventually be correctly charged (if they're getting enough energy overall).

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24v system charges at 24 or above but each battery only sees 12v 

do a quick multimeter check will show you what I mean 

Treat each battery as seperate with insulated clips - balanced charging would be nice but not essential 

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2 minutes ago, h4nd said:

BTW, those UNI-t clamp meters which go down to ~5mA dc are great for finding a random drain...

Can confirm this, zero it first. Surprisingly accurate compared to direct connection to a Fluke meter.

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9 minutes ago, h4nd said:

BTW, those UNI-t clamp meters which go down to ~5mA dc are great for finding a random drain...

I did try to check it using my multimeter but got nothing.

I basically know where the drain is anyway as I have one of my 24-12 DC DC converters hooked up all the time to supply 12v to the stereo stuff.

I have thought about isolating that stuff on a seperate small 12v battery charged from the 24v system but have yet to find the right charger for it.

Maybe I need to do that instead of the trickle charger. It would mean the stereo would remember stuff when I disconnect the main batteries as well...

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10 minutes ago, h4nd said:

1860126859_24-12Vstereo.thumb.jpg.4a8aa1df9079d687aad1a31946b6177a.jpg

Chuck a relay at it? The stereo would probably be OK changed between batt vs 12 from converter.

So that would power the idle circuit on the stereo from one of the batteries rather than the dcdc converter while the ignition was off? And hope there was enough stored power in the stereo caps to last the transition?

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1 hour ago, ThePog said:

So that would power the idle circuit on the stereo from one of the batteries rather than the dcdc converter while the ignition was off? And hope there was enough stored power in the stereo caps to last the transition?

Prezactly. The 'idle' circuit normally runs at tiny power, and the stereo normally draws more current (direct from the battery, thru that line) when the unit wakes up

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23 minutes ago, h4nd said:

Prezactly. The 'idle' circuit normally runs at tiny power, and the stereo normally draws more current (direct from the battery, thru that line) when the unit wakes up

Sweet, that may be a winner, it would make sense to keep that DC convertor switched off. If only i had a 24v relay lying around that I have not already used.

Although can you tell me the words I need to use when looking for a 24v to 12v charger, small but sufficient to keep a battery charged that is big enough to run the stereo, and also tell me how big that battery should be and whatever else I need to know please and thank you.

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Yeah you want a 12V charger with up to say 30-36V input.

Batt size depends on how long you want to run the stereo.

Charger current depends on how fast you want to recharge (battery will limit this itself in practice, unless you crank the V up), and if the stereo will be running at the same time you're charging (probably), but, at a guess, one of these would do it:

https://www.aliexpress.com/item/4000238066768.html

It's for solar, but it probably won't care, and you get lots of displays and functions and settings to fuck with :)

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22 hours ago, h4nd said:

Yeah you want a 12V charger with up to say 30-36V input.

Batt size depends on how long you want to run the stereo.

Charger current depends on how fast you want to recharge (battery will limit this itself in practice, unless you crank the V up), and if the stereo will be running at the same time you're charging (probably), but, at a guess, one of these would do it:

https://www.aliexpress.com/item/4000238066768.html

It's for solar, but it probably won't care, and you get lots of displays and functions and settings to fuck with :)

Right, one more question sorry.

I happen to have a small 12v solar controller and a battery.

I now intend to disconnect the dcdc converter supplying constant 12v to the stereo circuit and have it sitting in place as a spare for the one that drives the wipers etc. That one is on the 24v acc circuit. This should minimise the parasitic loss.

I am going to hook up the constant power circuit of the stereo to the battery through the controller, and have the 24v acc circuit feed the controller. This way even if I disconnect the main batteries the stereo will still remember settings etc using the battery. Then when the truck is running it will feed/charge the battery through the controller.

Do you see any problem with this?

I guess if the battery isn't big enough it will run down over time, but maybe I can have a relay that switches over to a small solar panel when not in use...

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On 01/09/2021 at 08:27, Muncie said:

Hey mate the way I read that is-

That charger needs the batteries separated for it to work eg: you could put an isolation switch in your link between your 2x 12v batteries then yes it'll charge them independently, but you would then need to disconnect your charger when you go back to 24v re-closing your link. 

It will try to balance both batteries to the same voltage but depending on your batteries internal resistance they will need different charging rates to achieve this, Eg one might charge at 3amps the other at 4 for 6 hours to reach 14volts or fully charged. 

*My explanation may be way off btw* more technical people can confirm or deny this.

 

 

It clearly states the 24v information. Wouldn't do this if it only charged 12v batts.

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