How do I connect a deep cell battery and a car battery to the same solar panel?

Forums › Gadgets, robotics, home automation, electronics (including wearables) › How do I connect a deep cell battery and a car battery to the same solar panel?

netspanner

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#255711 25-Aug-2019 08:45

In my campervan I have a solar panel that powers a new deepcell battery. However over winter when I don't use it the Van starter battery drains and I have to charge it manually. In a fit of inspiration I thought I could charge both batteries from the solar panel.

However the van battery is used for starting the van, and I don't want the start to draw power from the deepcell. Apparently deepcells don't like heavy starting currents. So I just can't connect the batteries to each other in parallel which, if I just run two cables from the panel controller, it will do I think.

Is there some sort of splitter i can buy that can stop power going from one battery to another and yet both be charged from the panel?

Jase2985

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#2305585 25-Aug-2019 08:52

could you just not put a switch in the line from the start battery to the charger, so you isolate it when you go to start the vehicle? maybe relay controlled from the ignition circuit?

Gordy7

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#2305622 25-Aug-2019 11:03

My camper van has a voltage sensitive relay (in series with a 40 amp fuse) between the deep cycle battery and the starter battery.

Click on thumbnail for a larger view.

Gordy

My first ever AM radio network connection was with a 1MHz AM crystal(OA91) radio receiver.

Gordy7

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#2305623 25-Aug-2019 11:09

netspanner:

.... Apparently deepcells don't like heavy starting currents.....

Check out your deep cycle battery model.... I recently saw that some deep cycle batteries can be used for heavy current starter applications.

Gordy

My first ever AM radio network connection was with a 1MHz AM crystal(OA91) radio receiver.

Linux

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#2305624 25-Aug-2019 11:09

Is the van 12 or 24 volts? I suspect 12 volts but just checking

k1w1k1d

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#2305634 25-Aug-2019 11:30

Wouldn't recommend using a VSR for your application.

The VSR is designed to charge an auxiliary/house battery from the vehicle alternator. The VSR will only link the batteries once the engine is running and the alternator has increased the vehicle voltage above the cut-in voltage, eg 13.6v.

The problem you will have is that the VSR will be on when trying to start the vehicle, so the auxiliary battery will try to assist the vehicle battery during engine cranking.

Redarc make solar regulators for dual battery installations, but they require the batteries to be the same construction type, eg both AGM, or both SLA, etc.

There are some "quick and dirty" methods that might work, eg switch and fuse, normally closed relay operated by vehicle ignition switch, etc.

I would suggest that you get an auto electrician to look at your van to see what is the best way to charge the van's battery.

Gordy7

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#2305675 25-Aug-2019 11:39

k1w1k1d:

Wouldn't recommend using a VSR for your application.

My VSR works....Maybe not correctly.... But the previous owner of my van did some other dodgy electrical stuff :-)

Gordy

My first ever AM radio network connection was with a 1MHz AM crystal(OA91) radio receiver.

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k1w1k1d

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#2305679 25-Aug-2019 11:48

Gordy.

Is the VSR sensing vehicle battery voltage or house battery voltage?

blackjack17

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#2305683 25-Aug-2019 11:59

Couldn't you simple put in a switch that disconnects the main battery from the deep cycle battery before starting the van?

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shk292

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#2305686 25-Aug-2019 12:11

Most yachts are set up this way - high-current battery for engine starting deep cycle batteries for the rest. The charging system ensures both are charged but are separate in supplying their load. So maybe talk to a marine electric specialist

Gordy7

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#2305693 25-Aug-2019 12:19

k1w1k1d:

Gordy.

Is the VSR sensing vehicle battery voltage or house battery voltage?

I don't know which side the sensing is wired.

I had a starter battery loose a cell or two last year and the van would not start.

The deep cycle battery remained ok.

So I would guess the sensing and isolation provided was ok.

Edit: I see that my VSR says Dual Sense.... Don't know how that would work with one sense wire.

Gordy

My first ever AM radio network connection was with a 1MHz AM crystal(OA91) radio receiver.

netspanner

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#2305909 26-Aug-2019 09:03

Thanks for all the interesting replies!

I have something that looks like Gordy's VSR that charges the Deepcell when the main battery is full. However it only works when the ignition is on. The current only goes one way, so the deepcell doesn't charge the main battery unless you press a button to do so.

This prevents the deepcell being used when you start the van unless its deliberate. (In the winter I get caught out now and then with the main battery running out as it also powers the alarm system)

So my solution is the simplest as a couple of guys mentioned, I'll just stick in a switch :-) . Until then I just moved the charging wire from the Panels over to the Starter Battery.