Author Topic: Battery to battery charging.  (Read 5226 times)

PhildOwen

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Battery to battery charging.
« on: April 16, 2013, 06:05:48 AM »
Hi Guys,

I'm not sure this is the right subforum to post this - but here goes. I have a camper van with two habitation batteries charged via solar panels. The vehicle battery is charged by the alternator when on the move. I would like to build a device which will allow the transfer of current from the habitation batteries to the vehicle battery when the vehicle battery is say 1/2 volt lower. Does anyone know of any circuit diagrams (examples) I can look at that do a similar function (or suggest a circuit layout)? I know there are products on the market that can do what I want but it would make an excellent first project for me.

Thanks for any help you can offer.

Phil.

SeanB

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Re: Battery to battery charging.
« Reply #1 on: April 16, 2013, 03:09:39 PM »
Shottky diode, cheaply obtained along with a heatsink as well from a deceased PC power supply.  Use the one on the 5V rail, and connect the 2 outer leads together and the centre to the other wire. Outer leads to the solar charged battery and the centre to the car battery, preferably using relatively thick cable ( 2.5mm minimum, 4mm better) and a 10A automotive blade fuse in line as well. The batteries need to have a common negative connection, provided by a short cable joining the camper batteries negative terminal to the chassis if there is not already one. You can also add a 20A rated switch to disconnect the circuit if not needed, simplest is to use a 20A MCB as it then can double as both the disconnect and a fuse.

PhildOwen

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Re: Battery to battery charging.
« Reply #2 on: April 16, 2013, 03:44:31 PM »
Thanks for the suggestion.

I'll go and re-watch Martin's Diode video. :)

PhildOwen

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Re: Battery to battery charging.
« Reply #3 on: April 17, 2013, 09:06:49 AM »
Shottky diode, cheaply obtained along with a heatsink as well from a deceased PC power supply.  Use the one on the 5V rail, and connect the 2 outer leads together and the centre to the other wire. Outer leads to the solar charged battery and the centre to the car battery, preferably using relatively thick cable ( 2.5mm minimum, 4mm better) and a 10A automotive blade fuse in line as well. The batteries need to have a common negative connection, provided by a short cable joining the camper batteries negative terminal to the chassis if there is not already one. You can also add a 20A rated switch to disconnect the circuit if not needed, simplest is to use a 20A MCB as it then can double as both the disconnect and a fuse.

If I'm reading this correctly I think you're suggesting using a transformer to build a battery charger. I've obviously made a complete mess of explaining what I need.

I would like some circuitry which will recognise when a battery (A) is 1/2 volt lower in charge than another set of batteries (B). When the situation is identified I want to flow charge 1 amp (max) from the other set of batteries (B) until they are equal in voltage. I also only want this to work in one direction from (B) to (A). Apologies if I'm getting the wrong end of the stick and your suggestion above is not building a transformer. Thanks for any suggestions.

Phil

SeanB

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Re: Battery to battery charging.
« Reply #4 on: April 17, 2013, 11:44:44 AM »
You use just the diode, as a low voltage drop isolator. You just are using it as a switch. No transformers involved at all. The PC power supply is just the cheapest and easiest way to get the diode and a heatsink for it.

PhildOwen

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Re: Battery to battery charging.
« Reply #5 on: April 17, 2013, 02:32:06 PM »
Thanks SeanB. :)

PhildOwen

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Re: Battery to battery charging.
« Reply #6 on: April 25, 2013, 06:18:43 AM »
Well guys I cheated :-[ - I bought a CBE CSB-2 which is unfortunately potted so I can't see the components inside ???

This is the description from the documentation:

When the leisure battery voltage exceeds 13.6V the device allows recharging of the vehicle battery (from the leisure battery). Charging current is set from 0.1 to 4 amp max. (dependent on the battery conditions). When the leisure battery voltage is lower than 12.5v the system is deactivated.

Can any of you technical wizards tell me what components would be used to achieve this function. Any suggestions will be gratefully accepted. I'd just like to know how this works from a discrete component point of view.

Thanks in anticipation.

Phil

SeanB

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Re: Battery to battery charging.
« Reply #7 on: April 25, 2013, 11:28:00 AM »
Simple, a diode in series with a relay contact. It charges when the donor battery is over 13.6V, and cuts off the relay when the donor battery drops below 12.5V Simple to do with a comparator with a little feedback ( sets the upper and lower voltage limits) and a single transistor to drive the relay, along with a low current reference source to give a reference for the comparator.

PhildOwen

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Re: Battery to battery charging.
« Reply #8 on: April 25, 2013, 05:36:07 PM »
Brilliant SeanB, that's just what I need to have a chew on and do some research!

You're slowly becoming my electronic's hero ;)