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Old 28 Jul 2007
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Location: Ghana
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Sterling Battery to Battery Charger (long!)

On a quick trip back to the UK I was looking for a way to reliably and safely install a charging system to run a second battery (powering only fridge and low powered gizmos - no winch). My criteria were that the system must not involve modifying the main vehicle cranking system, must be fail safe and as simple as possible. Previous home made systems have included split charge diodes and one using a really simple second battery joined with a massive switch coming through the seat box in a defender - but that was really designed to help with winching. This system is simply to charge (as best as possible) a big second battery for fridge, small inverter, camp lights etc... After a lot of web trawling I came up with a sterling battery to battery four stage charger. This apparently simply gets wired in between the cranking and auxilliary battery and is able to keep the cranking one charged but also fool the alternator into keeping the second battery well charged etc. Now I haven't yet installed it but the thing seems solidly built - they seem to be directed at marine installations so I guess should be fairly reliable. It also can accept solar panel input so I can wire up a big solar panel I found in a workshop. The unit also claims to be completely fail safe in that if it fails the aux battery cannot draw current from the cranking battery. Now to install it! Just wondered if anyone has tried such a device? Will let you know how it performs, but it 'looks' like a possible good solution to the good old split charging issue, as well as having a few (like plenty) LEDs to keep me happy!
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Old 28 Jul 2007
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Sounds good, do they have a website?
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Old 29 Jul 2007
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I think Sterling, whilst reportedly good gear, is a fairly expensive way to achieve what you want. In my bus i have 'house' batteries & cranking batteries 'joined' via a Redarc Smartstart voltage sensitive solenoid. (SB124) allows both sets of batteries to be charged via alternator &/or solar. see diagram (Note my setup is all charged at 24v, & a 12v 'house supply' drawn from the house batteries via a Redarc Charge equaliser.


Smart Start dual battery isolators by Redarc Electronics
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Old 29 Jul 2007
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sterling b2b

To get the best out of your second battery you really need to charge it properly ie with a four stage charger and never drain it to less than half charge, or the battery wont last long. Have a look at this site Self Build Motor Caravanners Club and trawl through the forum posts there have been a few about the sterling b2b charger. Also take a look here Sterling Battery To Battery Digital Charger - MarcleLeisure.co.uk there is a good discription of the charger and wiring diagrams. Hope this helps
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Old 29 Jul 2007
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battery switch

I used a simple boat battery switch....no electronics cheap and never failed. I would start the vehicle and then switch to aux batteries, this kept them charged to the max. I just had to remember to charge the vehicle battery once in a while. it has also the bonus of being able to turn to the off position a useful anti theft devise.

ebay item

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Old 31 Jul 2007
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Sterling B to B, 24-12V charger

I've had one of these in my Merc 917 for about a year now. It was fairly pricey (?£150) but was dead simple to wire in-just remember to use sufficiently large cables and it came with a couple of overide/cut-off temperature sensors which you fit to the alternator and the destination battery. It's worked extremely well and is very well built, i.e very physically tough. Can thoroughly reccommend as the simplest way to keep your leisure battery charged as much as it can be.


PS Marty how's the truck getting on?
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Old 3 Aug 2007
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To all who replied! I am going to install it now and will be really interested to see how it performs - especially with a solar panel providing power when the alternator isn't. Only problem is I really cannot fit another battery under my troopy's bonnet, so am now considering either a big battery maybe between chassis rails or in the cab - which I really don't want as I cannot get any fancy sealed AGM type batteries. My Landy just had a big lead acid battery in the rear in a wooden box, but the landrover was a bit "better ventilated". Think I will be going underbody!

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Old 21 Aug 2007
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Finally got round to fitting it, and I have to say the installation took a while! Basically the sterling and a 100ah battery now live in a home made large box in the rear of my troopy. As the batttery is not a sealed AGM or gel type battery there is a small vent pipe which comes off the battery and out to atmosphere via a small pipe along side the heavy cables (50mm2) powering the sterling. The cabling is probably overkill, but as I have it and some massive crimping levers I may as well 'go large' (can always rip out the cables and use as an emergency rope!). The box has a few extra power points (cigarette type) and a heavier amperage connector for a fridge wired in. In the future I will probably get a couple of anderson connectors so that the whole box could be removed from the vehicle as a (all be it large) portable power pack. The charger seems to do it's thing, when the vehicle starts it waits a few minutes to let a bit of charge into the starter battery, then starts boosting the second battery charge. Every twenty minutes it shuts down for a few minutes and eventually switching to a float charge. This weekend I plan on getting a clamp meter to check current draws and accurate voltages. The only thing is that the connectors for the sensors (temperature) are so flimsy and fiddly I ended up wrecking them, so the unit runs withought these safeguards. I will have to get out a soldering iron to fix them now. This seems to be the weakpoint on an otherwise solid bit of kit. In theory this setup should:
1) provide a better charge into both starter and second battery than alternator and split charge system alone
2) completely isolates the two systems unless the engine/alternator is running.
3) Should also provide a fast charge so even short trips or idling should charge up the second battery quickly.
I know some people think it is quite an expensive solution, but then National Luna split charge systems I have seen for about 170 quid - the sterling cost about 130, and should do considerably more in the way of charge management. Never thought I would become so interested in batteries!
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