Charge Indicator for Second Battery

[jims-terrano]

Does anyone know of a way of making an indicator light on my dash that will tell me when the second battery is in parallel with the main battery.

From the previous towbar wiring I have one of these split charge relays fitted http://www.towingandtrailers.com/self-switching-30a-combi-relay-tec3m.html. As I don't trust the internal switching I fitted a relay to the charge output of this unit which combined with a couple of fuses it connects the second battery to vehicle main battery. Have run this all summer without issue and I don't believe this was the cause of my flat battery. What I'm wanting to do is have an indicator that will tell me when the two batteries are linked so that if the relay sticks closed I can tell and do something about it. It's easy to have a indicator to show that the split charge signal is going to the relay but it's the actual link between the batteries I want to monitor.

Cheers

 

[Fez_uk]

Can you open that split charge relay? There's probably a line in there that could be used.

 

[solarman216]

Does anyone know of a way of making an indicator light on my dash that will tell me when the second battery is in parallel with the main battery.

it's the actual link between the batteries I want to monitor.

Cheers

Not easy at all, it is easy to fit one indicating the relay is powered, but that is useless if the contacts have welded together, the only way I can think of at the moment is to monitor both battery voltages, when joined they will be the same when separated they will read different, or maybe a shunt could be fitted to the connecting wire that will read any current passing but there will be times that they are connected but no current flowing, Rick

 

[rustic]

Hi Jim, The cheapest way is to fit a digital volt meter, search ebay "digital voltmeter"
You can pay 99 p, or £2.80 for a panel mount version.

The LCD versions, use very little power, and can be left on, or you can use a simple relay with the contacts wired in series with the battery supply to the meter. Relay coil supply could be on the accessory supply.

This has the advantage that you can monitor the actual voltage at the battery, even in use, so making sure you don't discharge the battery too much.

Buy 2, check your main battery too.

It is possible to build a voltage comparitor that electronically looks at the difference between both batteries, and puts a lamp on when the differential is below a certain threshold, this will cost quite a bit, plus design time etc but since there is a great solution for under £1 not worth me looking into.:thumb2

Hope it helps,
Best regards,
Richard

 

[Lazy-Ferret]

I think you are looking at it from the wrong direction.. firstly, buy a 200amp relay from Ebay, no more worry of the relay sticking, then as Rustic says, use two volt meters, one on each battery. On Suz's car though, unless one battery has a load still connected, the stay at the same voltage for a while, then both settle to 12.6volts for a long time, so not 100% proof.

To be honest though, even if the relay does stick closed, it would not run the batteries flat, just increase the risk of blowing the fuses in the link wire when you try to start the car with both batteries in parallel.

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