Club 80-90 Forums

I am going to fit a volt sensing relay between the main & leisure batteries. The charger from electric hook up is connected to both batteries in parallel so that when it is on a voltage will flow in the opposite direction ( from leisure battery to main ) to what it does when charging from the alternator ( from main battery to leisure battery ). Does anyone know if this could potentially damage the VSR or is this how chargers normally operate? In brief the supply will go to the output terminal of the vsr instead of the input terminal as it does in normal operating mode. Thanks

A little sketch of your wiring might be useful but from what you have said;
If you think about it, when the VSR is not activated (i.e. when engine is off), the voltage from the leisure battery is 'going' to the output of the VSR, so connecting the charger will just be the same as that - so it should be OK.
But a circuit diagram of your system would help clarify.

been researching this myself and it seems this is a popular method in america, also a trend in using acr (automatic charging relay)

Jeff J wrote:I am going to fit a volt sensing relay between the main & leisure batteries. The charger from electric hook up is connected to both batteries in parallel so that when it is on a voltage will flow in the opposite direction ( from leisure battery to main ) to what it does when charging from the alternator ( from main battery to leisure battery ). Does anyone know if this could potentially damage the VSR or is this how chargers normally operate? In brief the supply will go to the output terminal of the vsr instead of the input terminal as it does in normal operating mode. Thanks

Jeff, as this is a forum I should say that I am saying the following with your best interests at heart

When you say "The charger from electric hook up is connected to both batteries in parallel so that when it is on a voltage will flow in the opposite direction ( from leisure battery to main ) to what it does when charging from the alternator ( from main battery to leisure battery )." This to me either indicates that I am misunderstanding what you have done or are trying to say, or (and respectfully) you do not "understand" how electricity flows.

Basically, if anything is connected in parallel, be they batteries or bulbs or whatever, the current does not "flow from one to another" but is identically present at all places in the circuit at the same moment.

It won't damage your VSR But it's not the right way to go about it ! I will try and explain =

If your charger is connected in parallel to BOTH batteries then the starter battery will be getting drained whilst parked up (as well as the leisure battery), because there is a 2 wire connection between the 2 batteries via the charger, in effect linking them together as one big battery (i.e. in Parallel )

You may be disconnecting the charger when not in use = better, but still not good, as, if your leisure battery was low and you connect the charger as described, you will be allowing the starter battery to drain itself into the flat(ish) leisure battery.

However, simple answer = if you are using a correctly wired up VSR, you don't need the charger connected to the leisure battery at all Just connect it to the starter battery and as soon as the voltage rises to over around 13.6 volts (a matter of a minute or two assuming a good starter battery) then the VSR will kick in and automatically send a healthy charging voltage to your leisure battery It's what it's for

You could also of course just wire up the charger to the leisure battery, six and two threes really, but the former method ensures your starter battery is topped up too.

ghost123uk wrote: Just connect it to the starter battery and as soon as the voltage rises to over around 13.6 volts (a matter of a minute or two assuming a good starter battery) then the VSR will kick in and automatically send a healthy charging voltage to your leisure battery

Going off the subject John but why should it take 1 or two minutes for the charge voltage to reach the 13.6volts (approx) switching voltage?

Regulated voltage is fixed (between 14 and 14.5volts) and instant (as soon as the engine is running) however, and this is were there might be confushion, the amount of charging amps varies depending upon PD (potential difference) charge voltage/battery voltage. The regulator alters the strength of the rotor magnet (electro magnet) which directly controls current output (stronger magnetic field equally higher current output..weaker magnetic field/lower current output) the voltage remains more or less constant.

Martin

Your right of course Martin, it's pretty instant,

MidLifeCrisis wrote:A little sketch of your wiring might be useful but from what you have said;
If you think about it, when the VSR is not activated (i.e. when engine is off), the voltage from the leisure battery is 'going' to the output of the VSR, so connecting the charger will just be the same as that - so it should be OK.
But a circuit diagram of your system would help clarify.

Thanks, I missed the blindingly obvious on this one, sometimes I get bogged down & can't see the wood for the trees. As you say the leisure battery once charged will act on the vsr output in the same way as the charger, so it cannot be a potential problem. I've attached cct diag anyway though for any other comments. Thanks.

Ghost thanks for your post. I do thoroughly understand the flow of electricity I just don't know how to express myself very well. The basic problem for me was that I have never come across this type of electronic relay before & was unsure whether or not they were single or bi- directional. As reversing the polarity on some electronic components can have a catastrophic effect I did not want to blow a tenners worth of relay. Thanks for your response though.

Jeff - glad you have it sorted.
Circuit diagram was a great help - just one question;
What is the purpose of the 2 x 2-way switches between the charger, the lesiure batt and the output to the camper electrics?
I only ask because I know that (for example) the Zig charger unit states that you shouldnt use it to power the camper electrics directly (without a battery in the circuit) as it doesn't have the current (i.e. amps) capability. So if you have the switches there to allow you to run the electrics directly from the mains (bypassing the leisure battery completely) then you might want to take a look at the capabilities of the charger.
A better (simpler) way might be to have the charger connected directly to the leisure battery, and then the camper electrics connected to the lesiure battery via a simple on/off switch.

Thanks for your reply, my charger is definitely capable of giving the wattage I'll require & then some more. . With due respect your suggested alternative will actually increase the current drawn from the charger if the leisure battery is flat. Doing it my way means I can isolate whatever part I want to. The only mod I have now realised I need to make is a bypass switch for the vsr so that I can charge the main bat from the electric hook up should I need to. Thanks again.