VSR Relay

[domlee]

James Hortop (PBO 449, p80) suggests using a Voltage Sensitive Relay (VSR) as a means of achieving a split charging system. My local supplier has never heard of this, so could anyone suggest what exactly I should ask for and details of a supplier for such an item?

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[johna]

All relays are voltage sensitive so why use that description I do not know. However, you need a relay rated to suit the output of the alternator Lucas 33RA is rated 60amp at 12v as supplied by <A target="_blank" HREF=http://www.acornengineer.com>http://www.acornengineer.com</A> it should be inserted with the main contacts in the charging circuit alternator to domestic battery and the coil contacts in a circuit between the ignition light connection on the alternator and earth. Installed this way the relay will only close when the alternator is putting out more than the starter battery voltage.

I have also included a circuit breaker in the alternator - battery line to prevent heavy draw through this line when starting the engine IF the relay contacts ever failed closed and the charge in the engine battery was low.

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[bedouin]

I think these are commonly sold for connecting caravan batteries and so on.

They are called "Voltage Sensing" because they only switch on (which in effect connects the two batteries in parallel) when the voltage exceeds a certain value - in other words when the alternator is charging.

This connects the two banks so they can be charged in parallel when the engine is running and disconnects them when it is not.

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[andyball]

"voltage sensitive" usually used to describe a relay with some extra electronics meant to make it switch on/off at specific voltages. Idea being that you don't start charging the 2nd bank until the engine bank is at a certain voltage.

Often ok to arrange for both banks to be charged as soon as charge lamp goes out, even though engine battery voltage maybe not that high- but if you've a small starter batt./little charging capacity/lots of stop/start this wouldn't be as good.

As discussed here a few weeks/months ago.....think carefully first if you run very heavy loads on the domestic bank.







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[pvb]

Take a look here...

There are details of VSRs on the <A target="_blank" HREF=http://www.merlinequipment.com/prod_range.cfm?cat_id=83>Merlin Equipment website</A>. Merlin supply these products. It would be worth downloading their "Split Charging Guide" too, for background information. James Hortop is Marketing & Marine Sales Manager of Merlin.

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[domlee]

Thanks for the help everyone, the Merlin site was excellent and cleared my understanding of the matter (and a few other things!) up...

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