Hi folks

I've got an overland campervan which I'm currently driving around Africa. I recently found my electrical system has some severe shortcomings, and since I'm in the middle of deepest darkest Africa, I'm having to try sort things out myself.

I have 3 x 100Ah deep-cycle batteries, 2 x 60W panels and a Steca PR 2020 solar regulator. The Steca solar regulator uses PWM control to achieve multi-stage charging, resulting in optimum battery charging. However, at peak solation, I'm only getting about 7.5A from the panels, and often I'm taking more than that out.

Now I've also got a 15A DC/DC converter which runs off my truck's alternator, converts 24V to 12V, and connects the 12V output straight to the deep-cycle batteries. It works, up to a point, but won't be able to charge the batteries fully (apparently it will only achieve about 50% charging). I'd like to take advantage of the solar regulator's 'smart' charging system to fully charge my batteries when driving.

My solar regulator is rated up to 20A.
My panels produce maximum 8A.
My DC/DC converter produces maximum 15A.

What I've tried to do is connect the solar panels to the solar regulator when I'm parked up, and then when the truck is running, disconnect the panels and connect the DC/DC converter in their place.

I've done this successfully with a relay, but when I look at the solar regulator's display for the amount of current being produced by the "panels" (aka: the DC/DC converter), and the amount of current being sent to the batteries, both read 0.0.

Now the only determinable difference I can see is that the panels produce in the order of 16V, while the DC/DC converter is producing about 13.5V. From what I can see in the regulator's specs it says Open circuit voltage solar module: <47V. The operating instructions say Voltage range 12V: 6.9 V – 17.2 V. This leads me to assume what I'm doing should work.

Will what I'm trying to do work?
Am I doing anything wrong/stupid?
Why does the display read 0.0A when I think the converter should be producing 15A?

The solar regulator's specs are here.
The operating instructions are here.

Many thanks for all your help.
Regards
Steve

www.overafrica.org
www.overlandcamperforsale.com

Voltage is to low from the converter, try removing the converter and run 24 VDC straight to the controller.

Or skip the charge controller and connect directly to the converter. Problem with that is 13.5 volts will not fully charge 12 volt lead acid batteries.

__________________
Dereck, PE, MSEE
Moderator

Thanks for the reply.

The way the system used to work was the DC/DC converter connected straight to the batteries, so the +/-14V was charging the batteries, but as you say, not fully. I believe it is able to only achieve about 50% charge.

I can't run straight from the alternator, as it produces 55A at +/-26V when it's running. My regulator can handle max 20A.

The DC/DC converter is a standard switch-mode 15A 24/12V converter. Input is from the 24V batteries, output is +/-14V. It's turned on with a relay from the ignition, so only runs when the truck is running, and therefore the alternator is running (to prevent the truck's batteries from being drained when we're not running the truck)

I ran a test with a light bulb and my multimeter. Panels by themselves can light the bulb, and I get a reading of 2A (not peak solation, so can't get the full 7.5A that is theoretically achievable).
When I swap to the DC/DC converter the bulb burns brighter and I get a reading of 3.5A. ie: the DC/DC converter was producing more current.

Then I swap the light bulb with my Steca regulator. Multimeter for the panels connected reads the same - 2A. When I swap the panels for the DC/DC converter, current reads 0A.

Now the fact that the regulator's specs say it can handle an input voltage range of 6.9 V – 17.2 V when operating in 12V mode leads me to believe that it should be able to accept the 14V from the DC/DC converter and run with it.

Anyway, it obviously isn't, but I think it should. Strange?!

Thanks
Steve

Steve you alternator is capable of delivering 55 amps if demanded from the load, it doesn't always deliver 55 amps. Just like your battery is capable of delivering hundreds of amps, the load determines the current.

Your charge controller should regulate the current. If you are worried; do you have a large wattage resistor you can use to experiment with? Say a 2 ohm 10 watts?

__________________
Dereck, PE, MSEE
Moderator

Thanks for the response Dereck. Sorry it's taken me so long to respond - I've been on the road with limited access to internet. I'm now in Uganda (luckily Idi Amin is no longer around!)

The DC/DC converter produces ~15.8V (sorry, made a mistake on the previous post about the voltage produced) Now from what I understand, if the DC/DC converter just shoves 15.8V at 15A into the battery, it will charge it up to a point (roughly 50%), but is not capable of charging to full capacity. It could also cause over-charging and damage the batteries. To achieve 100% charging of deep-cycle batteries you need to use a 'smart' charging algorithm, (ie: my regulator has PWM charging)


I keep on going back to this quote from the Steca regulator's specs: This leads me to believe the regulator will use a DC transformer to alter the input voltage to the batteries to match it's needs. Ergo, 15.8V from DC/DC converter should work.

What different would connecting the alternator straight to the solar regulator have?

OK Steve you don't quite understand all that is going on, but it is not important that you do.

If your converter puts out 15.5 volts, that would take your battery past 100% left on long enough. If your PWM charger can operate from a range of 7 to 17 volts, means it has a Switch Mode DC-to-DC converter (not transformer) and should work fine for you with 15.5 volt input. Have you got a link or model number to your charger?

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Dereck, PE, MSEE
Moderator

I got a reply from the manufacturer of my regulator (it's a Steca PR 2020 by the way - look at my first post for links to specs etc)

I got this email from him (his answers after each of my questions)

Hey Steve I was kind of afraid of something like that with the power tracking circuitry and the pulses. Makes perfect since your converter is shutting down.

Really about the only way to do this is to use a charger made with 24 volt input to charge a 12 volt battery. I do not know of any commercial made units. Simple to design, but you would need the electronic skills.

My last idea is why 12 volts? Simplest thing to do is to use 2 12 volt batteries connected in series connected directly to the alternator via battery isolator.

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Dereck, PE, MSEE
Moderator