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| dorsetsmith Member Since: 30 Oct 2011 Location: South West Posts: 4554  |
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9th Jul 2017 6:39am |
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| ChrisCM Member Since: 10 Jun 2013 Location: Cornwall uk Posts: 572  
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Thanks Dorsetsmith,
I've already perused their site and, as you can see, theirs range from 20-500A! But no indication as to how they regulate the current so that using, say, the 20A VSR the liesure battery draws no more than 20A? Still confused 
Chris 2010 Defender 110 Station Wagon, Santorini Black. |
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9th Jul 2017 9:42am |
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| DuncanS Member Since: 06 Dec 2013 Location: Cumbria Posts: 299 
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The majority of the VSRs (Voltage Sensitive Relays) are purely just as they are named, voltage sensitive. This means no regulation etc etc, bar the voltage based open/shut.
They are ideal if you have auxiliary 12v sockets in the back, that you only want running if the engine is on, but you are wiring them from the permanent live. (Just one example) If you are wanting something that charges an auxiliary battery "properly" rather than just floating the charge up to the same level, you'll want a DC-DC Battery Charger. These devices where they show their current draw are based on maximum limited output rating. The reason they are so much more expensive is they will do the same bottom-up charging profiles and others that proper mains chargers will do, and they also aren't affected by a "smart" alternator in modern vehicles. Back to the use at hand, your best bet is to use something like this: https://www.durite.co.uk/itm/55875/Voltage...40A/072733 That will be more than happy linking up the two battery banks, and they are reasonably cheap and readily available at any remotely decent Auto Electrician supplier. Fuse at 100A with a mega fuse, and fit to an Anderson connector and bobs your uncle. The alternator will put out whatever its happy with, so having a 140a relay makes no odds and gives you plenty of headroom for future adaptation. The reason most people still use VSR's rather than going to the DC-DC chargers is twofold 1) They are too friggin expensive and 2) Most people aren't discharging their auxiliary batteries down to below 50% before restarting their vehicle. However I do always recommend that people fit the ability to plug a charger in to their aux battery so once every few months (usage dependent) they can do a proper "bottom-up" charge with a mains charger to keep it in good condition. Hope this helps Any further questions, fire away. North Cumbria Search and Rescue - Team Leader |
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9th Jul 2017 9:55am |
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| ChrisCM Member Since: 10 Jun 2013 Location: Cornwall uk Posts: 572
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Thanks Duncans,
Yes, aware of the dc-dc chargers, I have a Ctek S250 in my 110 and it works really well. It also has a split charge relay on the 13pin towing socket which also works well, but the same question applies to that as well! I'm happy that the cheaper VSRs will work and as this may well be a one off trip I don't want to spend too much! It's more seeking knowledge  , I like to think that I have a good basic grasp of electrical theory but this is eluding me. I am assuming that as the battery charge state lowers then the internal resistance of the battery lowers thus allowing more current to flow through the battery?, perhaps more than 20A so why doesn't it blow the fuse on a 20A VSR?
Perhaps I should just fit and forget and just rely on this electrickery to do it's job 😳 ? Chris 2010 Defender 110 Station Wagon, Santorini Black. |
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9th Jul 2017 10:13am |
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| DuncanS Member Since: 06 Dec 2013 Location: Cumbria Posts: 299
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Treat the VSR's just like automated gates. You'll get the same results as if you whacked jump leads across two batteries generally. In this instance, go for a 140a durite or similar for about £35 and you can't go far wrong. When you're running a CTEK unit, the transferred current is regulated by the charger, based on its point in the cycle. (Usually 3 stages, initial charge, main charge and float) This is to optimise life expectancy and charging time.
The amount of imbalance in the batteries, and what parasitic load is hanging off the end of it will massively affect the current draw into and through the cable, and (I'm also assuming here as I'm not the battery expert in my sales office) that there will be a theoretical chemical maximum it will take anyway. Generally (from my limited knowledge on the subject) for Good ole lead acid batteries its C/5 (a charge rate in amps of one-fifth the overall battery capacity in amp-hours) but I'm not entirely sure how that rationalises over to Glass Mat. North Cumbria Search and Rescue - Team Leader |
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9th Jul 2017 10:24am |
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| ChrisCM Member Since: 10 Jun 2013 Location: Cornwall uk Posts: 572
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Hi Duncans,
I'm going to go with a Durite VSR as you suggest, which I shall mount in my power pack box with an Anderson SB50 panel mounted, then use an Anderson SB50 connector mounted on a fly lead via mega fuse to the vehicle battery. This will give me interoperability with my 110 which has a fly lead mounted SB50 for powering my portable compressor which can then also charge the power pack which I will also use for Ham Radio. Thanks for all the info. Chris 2010 Defender 110 Station Wagon, Santorini Black. |
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9th Jul 2017 2:22pm |
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