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Posted by Brian Reay on October 3, 2006, 2:04 pm
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> Hi All
>
> This may be a bit OT but I couldn't think of anyone else to ask.
>
> I have been building a race timer and starter for the sailing club
> where I am a member. It runs off a 12V supply using car horns lights
> etc. Ar present we use a battery which has to be taken away to be
> charged.
>
> There is no mains electricity and electricity is supplied when needed
> (only a couple of hours a week) by a 3 phase diesel generator (about
> 20kW).
>
> I was considering connecting the race timer battery to the genset 12V
> starter system using a relay so that it would be charged by the 12V
> alternator when the generator is running in the same way a caravan
> fridge operates on 12V only when the car engine is running.
>
> I have had a look at how to do this and I was surprised to see that
> the 240V (415V) systems are not separated at all. Terminal blocks,
> PCBs etc are shared by both sytems.
>
> It occurs to me that in a fault situation there could be up to 415V in
> the 12V system so that automotive type lamps horns connectors etc
> would be inadequately insulated.
>
> Is this a real risk or is it OK to go ahead and use the 12V system.
>
> Would it be better to plug a battery charger into the 240V output of
> the generator and just leave it connected.
>
> I'd be grateful for any comments or suggestions.
It all rather depends on the way the system is wired / configured and the
nature of the fault.
Does the generator have separate windings for the HV and LV (which I would
expect) and just the control circuitry shares a PCB and terminal strip etc?
If so, a fault (eg a short) on the latter group could result in HV on an LV
circuit. However, if the unit is maintained, I'd think the risk small.
A "plug in" charger would get around that problem but probably is overkill,
in my view.
Brian
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>
> This may be a bit OT but I couldn't think of anyone else to ask.
>
> I have been building a race timer and starter for the sailing club
> where I am a member. It runs off a 12V supply using car horns lights
> etc. Ar present we use a battery which has to be taken away to be
> charged.
>
> There is no mains electricity and electricity is supplied when needed
> (only a couple of hours a week) by a 3 phase diesel generator (about
> 20kW).
>
> I was considering connecting the race timer battery to the genset 12V
> starter system using a relay so that it would be charged by the 12V
> alternator when the generator is running in the same way a caravan
> fridge operates on 12V only when the car engine is running.
>
> I have had a look at how to do this and I was surprised to see that
> the 240V (415V) systems are not separated at all. Terminal blocks,
> PCBs etc are shared by both sytems.
>
> It occurs to me that in a fault situation there could be up to 415V in
> the 12V system so that automotive type lamps horns connectors etc
> would be inadequately insulated.
>
> Is this a real risk or is it OK to go ahead and use the 12V system.
>
> Would it be better to plug a battery charger into the 240V output of
> the generator and just leave it connected.
>
> I'd be grateful for any comments or suggestions.