Car charging battery

[Zebb]

Hi

I have a Astra van mk5, I want to add a second battery (100amp leisure battery) in the van for camping and for topping up my bike battery back up, do i need to add a relay to the system, so the van will charge it up.

As there is a load of electrics in the panel in the back, can I use any part of this,it also has 7 pin standard towing electrics can any part of this circuit be of any use to my requirements.

Any help please thanks.

 

[Old_Dave]

You need a split charging relay.. The wiring is as in this picture



The relay would be fitted near to the alternator & main battery and needs a separate charging cable to the 2nd battery, so it's unlikely that your existing wiring would be available for using (cos it would be dedicated for other porpoises ... Lol)

But if you have a spare cable of suitable size for charging then you can use it.


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[Alan Quay]

Alternatively, a VSR (voltage sensitive relay), which is slightly more simple to wire, as you don't need to find the 'charging light' connection. The other advantage is that your main battery gets charged first, as the VSR kicks in at (something like) 14v.

Probably a little more expensive though.

 

[Zebb]

Thank you very much for the help, I will put the relay near the standard battery and run a cable of the correct size to the leisure battery a few feet away.

Again many thanks.

 

[Zebb]

Alternatively, a VSR (voltage sensitive relay), which is slightly more simple to wire, as you don't need to find the 'charging light' connection. The other advantage is that your main battery gets charged first, as the VSR kicks in at (something like) 14v.

Probably a little more expensive though.

Mike thanks for that I will take a look at those relays too.

 

[Alan Quay]

Just had look on eBay, about £35 quid delivered. Basically, connect two wires from VSR to existing batt, take thick cable from VSR to leisure batt, connect leisure batt negative to chassis.

 

[Old_Dave]

Just to say that the quick / dirty way I showed would need a relay and fuses rated to the alternator output... Which will be bigger than shown, the other method as given by Mike is a much better solution


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[Zebb]

Thanks I will go for the vsr, i take it i still need inline fuses to protect the circuits, will it state on alternator the output current,?

Cheers

 

[Old_Dave]

Yes and maybe ... Lol




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[Zebb]

Ok understood, many thanks for your help.

 

[the_killjoy]

Being naive, why cannot it simply be wired in parallel with the original battery ?

 

[Zebb]

Battery isolator (or split charge relay) allows an auxiliary battery to be charged by the vehicle's system, yet not participate in engine starting. It also prevents the starting battery from being run down by your equipment when the engine is off.

 

[mike killay]

I have just fitted an automatic relay to the campervan I am building.
They are simple to wire in and do not need a command wire from the alternator.
Most types have an adjustment pot through a hole in the side.
When fitted, they should come on about 30 seconds after the engine starts and stop about the same time after the engine stops.
Remember to fit fuses at both of the batteries so that if a wire disconnects, neither battery can still keep sparking.
Use 30 amp wire to connect the batteries and fit 20 amp fuses.

 

[benjy_a]

What you need to bear in mind is that your alternator is capable of putting out probably around 100A when your battery is flat. The alternator on my campervan is 170A.

So...if your leisure battery has been run down low, when you start your van the voltage sensing relay will connect the alternator to it and potentially your battery will draw 100A, thus blowing a 20A fuse or melting your wires.

In practice, many people get away with using these small relays as they never run the (fairly low capacity) leisure battery low enough for it to try to draw so much current. A 30A relay with 20A fuses is not sufficient to properly charge a flat leisure battery directly from the alternator (and yes I know you shouldn't be running it flat but same will apply if you let it run low by accident).

I have a 30A voltage sensing relay which controls a separate 150A relay with nice chunky cable and fuses connecting the alternator to relay and relay to battery. I learned the hard way after several blown fuses and a melted relay.

 

[Deleted member 4366]

Don't cheat on the battery by trying to get away with a cheap ued one. You'll need a good 100ah minimum one to charge a 36v 10aH one from flat with a charger and inverter. It might be a good ide to have the engine running while you charge to preserve your battery.

 

[Zebb]

Again thanks for the replys, most helpful, I already have new 100amp leisure battery and inverter, so just need relay and some bits then all ready to go, I wont be running the battery low too often but understand what will happen if I do.

 

[benjy_a]

You should get away with it with light use, I have 250Ah battery bank and when it's 40% discharged it sucks well over 100A from the alternator but that's powering a whole host of gadgets on the campervan for 2/3 days between charges.

Just make sure you have the fuses so worst case will be that you blow them.

 

[Alan Quay]

The VSR's on eBay are rated at 140 amps.

 

[benjy_a]

Plenty I should say...just need massive fuses and a short (fat) cable run from alternator to battery to avoid voltage drop. The relays being discussed earlier in the thread were the rubbish 30A jobbies such as the ones in Halfords etc.

My method was very cheap; £5 low current VSR and cheap 150A relay costs less than a 140A VSR.