# battery charging when driving



## vandad (Mar 1, 2011)

Advice needed. I don't have an on-board battery charger but rely on the leisure battery charging whilst on the move. My leisure battery (Elecsol) is connected to the vehicle starter battery with an intermediate self-switching relay (Smartcom); the system works fine although the amount of charge is limited by the daily mileage I drive. Although I have a basic understanding of 12v electrics I'm not sure about whether the charge should be regulated as when a battery charger is used ie battery charger delivers at a rated amp/hr. I'm not sure whether the Smartcom regulates the rate of charge - I'm fairly sure it doesn't.
My Q is does the leisure battery require a regulated charge or is ok to connect directly to the starter battery using a relay and in-line fuses to protect it. My concern is that if it's not regulated and the leisure battery is depleted then a 'thirsty' leisure battery is going to demand a fairly high current and although in-line fuses give protection this may not be good practice. My vehicle is a VW T5 camper.


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## pieterv (Feb 3, 2009)

A modern multi-stage charger will start with a set current (whatever the charger can provide, assuming the battery is discharged enough to take it), and when the battery gets up to usually 14.3V or 14.4V keep the voltage there for a number of hours (depending on battery type) before switching down to a lower voltage (usually 13.8V) to give a maintenance charge.

Your alternator is unlikely to go higher than the 14.4V (and might be considerably lower on an older vehicle), so there is no risk of over charging. Theoretically the current supplied by the alternator in the beginning could be too high for the battery, though, but I don't think that is something to worry about too much unless your battery is very small.

The smartcom is indeed just a relay, so your battery will get whatever the alternator puts out (minus losses in wiring and the smartcom itself).

People are usually more concerned that the alternator doesn't charge their leisure battery enough, rather than too much, and that is the reason they go for something like a Batter-to-Battery charger (B2B), which basically is a multi-stage charger, but driven from the alternator rather than mains.

Pieter


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## Hurley (Mar 2, 2011)

Hi, I actually have the same problem, I could not tell if the charging is regulated or not, and I am worried about my new LED lights inside, would they get too much voltage or current.


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## pieterv (Feb 3, 2009)

You only need to worry about the voltage, the current depends on the voltage.

Your alternator will defintely regulate the voltage, but it will be above 12V, otherwise it couldn't charge the batteries.

Check the spec for the LEDs, that might tell you for what voltage range they are meant, but I think most people use them without problems.


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## Hurley (Mar 2, 2011)

I want to use this light 12 SMD G4 LED which works at 12V, but maybe this other light 10 SMD G4 LED is actually safer, because it has a different voltage range?
Or do you think I should use the one with more LEDs working at 12V and add an external regulator?
You see, the reason I want to make this sure, because there is no point in paying so much for these lights if they fail within a short time because they are not compatible with my system.


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## trevorf (May 16, 2005)

But surely you do not have your LED lights on in the back of the van whilst driving ????????





Trevor


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## pieterv (Feb 3, 2009)

trevorf said:


> But surely you do not have your LED lights on in the back of the van whilst driving ????????
> 
> Trevor


No, maybe not, but you would have the same raised voltage on EHU to charge the batteries. I still don't think it is a big issue, though.

The second LED linked to above indeed specifies a voltage range that is more than wide enough, so might be the safer option. You can, however, get LED replacement bulbs on Ebay that look very similar to the first on linked to for about half the price.


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## Ken38 (Mar 24, 2009)

Many people, including myself, use LED lights when on EHU. I bought mine at a show and they were meant for 12 volt vehicle systems.

I would expect virtually all 12V LED lamps to be designed for this. When LED lamps were expensive and new they probably were for the designer market and sensitive but now they are more robust and cheap.

Your relay system will not overcharge the leisure battery. The voltage is regulated by the alternator regulator.

If your leisure battery is low it will grab the lion share of the charge but only after the vehicle battery is charged enough for the relay to cut in. So even if you are doing relatively short journeys the vehicle battery will get some recovery of charge. If you do lots of short journeys and use lots of vehicle fans, heated windows, headlights then you will get virtually no charge back in either battery.

So don't worry as long as you don't put an old fashioned charger on the battery and cook the battery your LEDs are safe. If they are sensitive then throw them away when they blow and buy some correct ones!


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