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Post Info TOPIC: Keeping batteries charged
Terryt


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Keeping batteries charged
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Coaster. start batteries 24v. House batteries 12v. While sitting at home I have it connected to power. A 24v charger looks after the start batteries and a dc dc charger supplies 12v to the house batteries and keeps them charged. The 24v charger is connected to 240v. I assume the dc dc charger takes what it needs from the start batteries. Either way it works a treat and both sets of batteries stay fully charged. Having the 240v lead connected is a bit annoying and I would like to get rid of it. I also have a 300w inverter installed and connected to house batteries. Everything is mounted in the vehicle.

I have thought of 2 ways to get rid of the 240v lead both involving buying a new solar panel

a)  permanently mounted solar panel on carport through a new controller to the 24 v battery bank which will then charge to house batteries as already happens. Would cost a new controller, some cable and anderson plugs

b)  cable from the new panel to the dc dc charger and run the 24v charger off the inverter. Max output of the charger is 3.5amps. Dc DC would look after house batteries. 24v would look after start batteries

Pros and cons of both. Any better suggestions. What size panel would do the trick? I was thinking it wouldn't need to be too big. Comments would be welcome



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Bobdown


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Hi Terryt,

Not exactly the same thing but not sure if you have solar on the coaster, but in my case I have 2 x 150 W on the roof of the van which is parked in a gable roofed carport when not in use.

I installed 2 clear Alsynite sheets over the solar panels which is North facing, my van batteries are constantly 13.2 V to 13.5 V trickle fed with about 60% SOC on a sunny day. I power the fridge up

2-3 days before we go away and rarely use 240 V power from the house, works a treat.

IMG_2897.JPG



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Terryt


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Thanks. That is certainly an option and if I had my **** together when putting the carport up it probably would have been the best option. To retrofit the sheets would be expensive and hard.

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Craig1


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G'day Terryt,
A professional roof fixer would do this in no time at all. I have had a quarter(40 sq metres) of my house roof on and off in 2 hours, replaced insulation /sisalation.

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Cheers Craig
T1 Terry


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Hi Terryt, If you look on evil bay you will find second hand house type solar panels cheap as chips and close to where you live. Buy a cheap 24v PWM regulator from evil bay for around the $20 mark and wire the solar panel to an Anderson plug, then a second Anderson plug to the solar input of the cheap regulator and mount that in the coaster close to the start battery. When you need to keep the start battery topped up simply plug the two Anderson plugs together and the cheap solar panel attached to the carport roof will keep the start battery topped up.
It doesn't matter that the voltages don't match up between the solar panel and the battery, just as long as the solar panel Vmp (marked on the back of the panel) is higher than 28vdc. You aren't looking for the maximum efficiency, just a cheap and easy way to keep the batteries charged when the vehicle is parked up under the carport.

T1 Terry

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Terryt


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T1 Terry. I live in the boondocks and even tho I tried I could not get a secondhand house panel locally. I did get a second hand 150w panel in excellent nick and for a good price. I also have a spare 12v 24v controller. I originally thought the mention of 24v meant the controller would charge my 24v start battery setup but alas alack I now realize because the panel puts out less than 28v it won't work. So I am back to using the new panel to supply the dc dc charger which charges the house batteries which run the inverter which powers the 24v charger that charges the 24v battery bank. Almost sounds like perpetual motion? I have plugged it all in and it seems to do the trick.
OR would it be possible to charge each of the 12v start batteries in the 24v bank as a 12v battery using the spare controller. ie run a positive and a negative from the controller to each battery or would that make the smoke come out. The spare controller is a pwm that came with a solar mat.
Any comments would be appreciated.

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T1 Terry


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You would need to build 2 x 12v charging systems, each with their own panel and controller. System one is connected between battery negative and 12v battery positive. System two is connected with the negative on battery 2 negative and the positive on battery two positive. Even though measured from battery one negative the voltage battery 2 negative is greater than 12v+ the system two does not see battery one negative, it only sees battery two negative so as far as it is concerned the voltage at that point is 0vdc and the positive terminal is +12vdc.
A bit to get your head around, but it does work and works well by keeping both 12v batteries reasonably balanced to each other. The important thing is, system two can not have any of the negative connections come in contact with the body negative. Best add a few fuses in the negative side of system two just to be sure, otherwise and contact between the negative of system two and the body would be a dead short across battery one and quite likely cause a wiring fire.

The other option is to find a voltage boosting type MPPT controller that can bring the output voltage up to the 28.8v you need to charge the 24v battery from the 12v panel. Maybe something like this www.ebay.com.au/itm/DC-DC-Boost-Buck-Step-Up-Down-Converter-Module-3-3V-12V-24V-Solar-Charger-Power/253930272363 but it might need 2 in parallel and a cooling fan

T1 Terry

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You can lead a head to knowledge but you can't make it think. One day I'll know it all, but till then, I'll keep learning.

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Terryt


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Thanks for that Terry. For now I think I'll let the panel look after the house batteries only and every few weeks give the start batteries a tickle via the inverter and the 24v charger

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