Mains supply puts 15volts on leisure battery - ok?

[cbeeson]

My Bongo conversion has a 75Ah 'maintenance-free' lead-acid leisure battery. On a mains hookup, the 12v supply is provided by an Estrasil PB10 Mk6 transformer, specified output being 12voltsDC at 7.5A continuous, 10A intermittent.

I've recently fitted a Nasa battery monitor for the leisure battery. I'm a bit concerned to see that when the battery is being charged by the Estrasil, and has reached full charge, the terminal voltage is reaching a touch over 15volts, although the current has dropped to well under 1A. What I've read on the Web suggests that the battery should be fizzing with such a voltage on the terminals - and being low maintenance, I can't get to check the electrolyte levels. I also wonder whether it might harm the fridge electronics.

Any advice or comments welcome!

[Tony x]

15 volts is a bit high - sealed batteries have to be charged at a lower voltage than vented to prevent the build up of hydrogen.
Not sure about the fridge but I suspect it would be ok

[g8dhe]

Yes that is to high if the display is correct, perhaps check with a multi-meter if possible, anything above 14.6Volts will lead to gas hydrogen and oxygen being created, which is NOT a good idea!!

[windywatson]

Hi, with respect to the voltage being high you asked if it might damage the fridge? If the fridge is of good quality the incoming supply may well be passing through a circuit to regulate the voltage. Many so called 12v dc devices are manufactured ether with a large tolerance on input voltage or regulator to manage the voltage internally. It should be possible to check what the range is, as it is often specified by the manufacturer in the technical specification or on the details on the manufacturers label usually on the back some where.

cheers

[Diplomat]

I very much doubt that fridge manufacturers would ever put a regulator on the the 12v input. There simply is no need. The designer would assume that the maximum they would ever see thrown at them would be the full output of a car alternator across a dud battery and treat that as the worst case.

Putting a regulator in series with the fridge motor or absorption heater would involve extra cost and result in throwing away energy as heat.

The place for a regulator is in the charger, if it is a half decent one.


Frank

[cbeeson]

Thanks for the responses. I realise that 15 volts is deemed on the high side, but the Estrasil is quite widely used on caravans and campers, I understand. I'll see if I can get a response from the makers.

[cbeeson]

The power supply is an Estrasil PB10, made by B C Electrical Techniques Ltd near Aylesbury. I've now had some correspondence with the company, though it hasn't really resolved the issue.

The company generally designs and sells transformers. The PB10 appears to me to be basically a mains transformer, a rectifier, and a large capacitor to smooth out the output ripple. The internal resistance of the transformer regulates the current to some extent, rather like an old and basic type of battery charger. The manufacturers say it's intended as a power supply rather than a charger, but state that it will also keep the leisure battery charged.

I've pointed out to them that wet lead acid batteries will gas if the terminal voltage is taken as high as 15v, which is what I'm seeing here, and that they shouldn't be left at this level for any length of time - as when spending several days on a site hookup.

It seems these units have been quite a popular fitting on caravans and camper conversions, so if you get through batteries rather quickly (as I was doing) then it'd be a good idea to check the terminal voltage with a multimeter when you're on hookup.

[g8dhe]

Does the transformer have some additional mains taps i.e. 230v 240v 250v if so try putting it on the highest voltage that will cause the secondary to be at its lowest value. It may be a case of moving a wire on a chocblock type connector, or possibly an extra tap on the transformer itself which might need soldering to change over.

[cbeeson]

Does the transformer have some additional mains taps i.e. 230v 240v 250v if so try putting it on the highest voltage that will cause the secondary to be at its lowest value. It may be a case of moving a wire on a chocblock type connector, or possibly an extra tap on the transformer itself which might need soldering to change over.

No, nothing like that. It's a sealed unit. Anyway, putting up the voltage tap from, say, 230v to 250v would only bring the 15v output down to 13.8v, which is still on the high side. I'm afraid I think the designer has simply got it wrong. It'll be ok as a power supply, but not up to the job as a charger.

Anyway, I've given up and ordered a Ctek!

[Bob]

Good choice, very pleased with mine.