Fitting a Slave Battery

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James_A

James_A

New Member
Posts
57
Location
Preston-way
I'm thinking of fitting a slave battery to my FL. I can't see any space in the engine bay, so after talking about it with a guy at work we thought of the following (this may qualify for 'two half wits don't make a full wit'!):

Fasten a battery box in the boot. Into the battery box put a red-top sealed racing battery (or similar) so that you don't get fumes when it's charging, and connect the battery to the wiring for the caravan socket (S-type???).

Questions (as I've never been in a caravan, yet alone wired one in!):
(1) Will this charge the battery when I'm travelling, or do I need additional charging circuitry (usually in the caravan)?
(2) Can I/How Can I wire this in parallel with my existing battery (is it just a case of conencting the negative to a suitable chassis point, and feed my accessories from the positive). If I can;t do this, then I'll just runn my accessories direct from the 2nd battery and earth them back to it.
(3) Is this a bad idea from the start / Is there a better way that doesn't cost a fortune?!!

Thanks for any advice.
James
 
why do you want a slave battery? and what do you want to run from it? I ask because depending on load, the cable capacity will vary - you may need to run cables direct from your main battery back. Have you considered upgrading your present battery to a higher wattage type?
 
At most I'll be drawing about 6 Amps. It's intended to run my rally radio for long periods of time (and occasionally my eberspacher) whilst in the depths of a forest. At the moment I'm paranoid about running my engine every hour or so to keep the battery topped up. (A 2nd aim is to make it easily removable/refittable for 'normal' use)
 
I'd not thought of one of those.... I didn't think that they'd be powerful enough. I'll have a look-see, it might just be a cheaper alternative. Ta.
 
With a bit of fiddling around, you can get a massive battery in the engine compartment ...

Trophy_Freelander4.jpg


The power pack might be a better solution, though.

Cheers

Blippie
 
I have one of those power packs. At that price you cant go wrong! plus you can charge from auxillary socket when engine is running.

I was caught out just before Christmas, battery died, tried to jump start but pack wasnt fully charged - about 12v, not the usual 13-14v

Wouldnt crank over for me so had to resort to my RAC membership. Not one person had jump leads in the vicinity.

Ahh well there goes my 10% discount on next years membership.

If you are going to get a spare battery then go for a leisure/caravan style one with a longer amp/hour rating
 
My word blip that is a big battery. . . .and what may i ask is the big black fing on top er ya engine cowel ?. . .
 
ming said:
My word blip that is a big battery. . . .and what may i ask is the big black fing on top er ya engine cowel ?. . .
Click to expand...

To squeeze the battery in, you need to move the air filtery bit up and ontop of the engine. Quite handy as it raises the wading level rather. Who needs a snorkel?

Cheers

Blippie
 
James_A said:
Questions (as I've never been in a caravan, yet alone wired one in!):
(1) Will this charge the battery when I'm travelling, or do I need additional charging circuitry (usually in the caravan)?
(2) Can I/How Can I wire this in parallel with my existing battery (is it just a case of conencting the negative to a suitable chassis point, and feed my accessories from the positive). If I can;t do this, then I'll just runn my accessories direct from the 2nd battery and earth them back to it.
(3) Is this a bad idea from the start / Is there a better way that doesn't cost a fortune?!!

Thanks for any advice.
James
Click to expand...

I began with the caravan setup using an 'S' setup to charge a second battery in the boot of old car. I found that it worked ok, but would not charge at more than about 5-10 Amps. (so a 50ah battery would take between 5 and 10 hours to charge.)

I upgraded by main vehicle battery from 55AH to 110AH - this gave me double the capacity meaning that I could leave the sidelights on all night (if parked on a road) and still start the vehicle in the morning.

For camping I installed another 110AH Leisure battery in the boot of my car, but instead used a 100Amp relay and winch cabling to connect it to the positive terminal of my vehicle battery and negative to car bodywork (or negative terminal).

This proved more successful. My fridge ran continuously and would operate until the slave battery fell to 4v. The main vehicle battery would start the car and then the relay would connect the slave battery enabling charge to be applied. After 30mins or an hours worth of driving around, my slave battery was upto 13v and would last about another 4 days powering the fridge (which drew 4 amps when thermostat cut in).

My vehicle had an 85AH alternator that was capable of keeping both batteries topped up with little driving.

Hope this helps. Autoleads do a split charge kit inc relay, fuses, switch, terminals and cabling for £30 - £35 on the web.

Any further questions - feel free to post.
 
G13SJC said:
I began with the caravan setup using an 'S' setup to charge a second battery in the boot of old car. I found that it worked ok, but would not charge at more than about 5-10 Amps. (so a 50ah battery would take between 5 and 10 hours to charge.)

I upgraded by main vehicle battery from 55AH to 110AH - this gave me double the capacity meaning that I could leave the sidelights on all night (if parked on a road) and still start the vehicle in the morning.

For camping I installed another 110AH Leisure battery in the boot of my car, but instead used a 100Amp relay and winch cabling to connect it to the positive terminal of my vehicle battery and negative to car bodywork (or negative terminal).

This proved more successful. My fridge ran continuously and would operate until the slave battery fell to 4v. The main vehicle battery would start the car and then the relay would connect the slave battery enabling charge to be applied. After 30mins or an hours worth of driving around, my slave battery was upto 13v and would last about another 4 days powering the fridge (which drew 4 amps when thermostat cut in).

My vehicle had an 85AH alternator that was capable of keeping both batteries topped up with little driving.

Hope this helps. Autoleads do a split charge kit inc relay, fuses, switch, terminals and cabling for £30 - £35 on the web.

Any further questions - feel free to post.
Click to expand...

Interesting, electrics arent really my thing.

Query - is there any chance that the alternator would charge the slave battery and not the main battery?

Whats the rating on the relay if the amps were higher from the alternator?
Racemettle ltd can rewire the alternator for higher ampage around 110A
 
LR1796 said:
Interesting, electrics arent really my thing.

Query - is there any chance that the alternator would charge the slave battery and not the main battery?

Whats the rating on the relay if the amps were higher from the alternator?
Racemettle ltd can rewire the alternator for higher ampage around 110A
Click to expand...

As the two are connected together (when relay energised), they simply draw the current that they need. I fitted a voltmeter and the volts were always between 13 and 14 whilst engine was running. In four years of using this system I have never experienced a drained main vehicle battery.

Relay was rated at 100A - I didnt have any problems. You could use a battery isolater to switch the slave battery on and off manually - this would be cheaper than using a relay and would be safe for craking amps (upto 500A)

Other points:-

The slave battery can be left in the car - even when not needed. If your main vehicle battery decides that it wont turn over the engine, then a quick turn of an isolater links the other battery to act as a jump starter.
 
If you want to fit a secondary battery - then a split charge relay will do it.
Switches additional power to charge auxiliary battery plus feed to fridge or other device.
Fits 12v neg earth cars. Only operates when the alternator is charging.

I can supply these if you wish.
 

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