Club 80-90 Forums

Maybe a crazy question - and it's late at night so I may not be think straight anyway ...

I know that if I connect my 2 leisure batteries in series I will get 24 volts, but can I do this in a separate circuit concurrently to having them in parallel running the normal 12v fusebox?

The reason I ask is that my Waeco CF50 fridge is playing up, probably the Polyfuse issue. I'm told that the fridge will work on 24 volts, hence the idea of creating a new circuit just for the fridge.

Thanks to the electronics boffins for any help!

The idea is sound, in fact fire alarm systems do this by putting two 12v batteries in series but your problem will be charging the 24v battery. I don't know how much current these fridges draw but you may be better off with a 12v to 24v DC to DC converter. Or 12v DC to 240v AC inverter if the fridge runs on mains.

Adeybruce wrote: but can I do this in a separate circuit concurrently to having them in parallel running the normal 12v fusebox?

You can't have them in series and parallel at the same time.
You could use a double pole changover switch to swap between series and parallel.
While they're in series you can tap off 12v from the terminal between the two to run the normal stuff off ONE battery and run the fridge only from the 24v terminal (both batteries).
You could then switch to parallel for charging or running everything but the fridge, the split charger should cope with the different states of charge but an intelligent charger won't.
I will do you a diagram if this isn't clear. the switching is a bit complicated.

The simple way would be to connect them in series, tap off 12v from one battery for 12v stuff and 24v for fridge.
Your split charger will then charge the first battery and you'll need to charge the second one separately.
Not ideal I know.
Better to fix the fridge.

Setp up and step down converters are so bloomin useful. I have a small one that steps down to 4.5v since there are so many circuits that seem to need that these days. No reason why it shouldn't work to step up to 24v.

The only caveat with these stepup/down converters is - check the soldering on the board with a magnifying glass as quality control is poor. I automatically resolder the pins on the in and out terminals as I have had a lot of failures here due to poor soldering.

Gentlemen, thank you for your advice. I think I will go down the route of the 12 to 24 step up converter.

To get me out the crisis I have been using my power inverter to run the fridge off mains voltage but this seems to be pretty inefficient so hopefully running through a 24v converter will improve the situation.

Just make sure the converter is beefy enough to supply the amps required by the fridge although personally, I'd be using gas rather than battery anyway.

1200W beefy enough?
I prefer to use the gas also but he hasn't got that option with his box. Looking at the specs though it just says 12/24v as though it runs on both voltages with no sign of a switch to go between the two so no need for a stepup to 24v at all.

Well.... have you just used it on 12v as intended?

Oldiebut goodie wrote:Well.... have you just used it on 12v as intended?

I wondered that. As it copes with dual input voltages, if it doesn't work on 12v I can't see how 24v will kick it into life but then I don't know what the "polyfuse issue" is.

Is your battery voltage high enough? If the battery monitor is set to low will it work?

From the manual ...

If the cooler is operated when the vehicle ignition is switched off, the cooler switches off automatically as soon as the supply voltage falls below a set level. The cooler will switch back on once the battery has been recharged to the restart voltage level.

Intended purely for operation when the alternator is going then. I doubt this unit is going to work for you.

Just the same as adding a LVD yourself to the leisure circuit.

(Don't think that he is talking to us - has Scotland gone already )

Gentlemen, thank you for your advice. Indeed the fridge can accept 12-24 volts, but my understanding is that when mains voltage is used (separate input) that it is stepped down internally to run on 24 volts; and the fridge works just fine this way.

The fridges have a known common fault - a Polyfuse by all accounts - that overheats on 12 volts. The cunning plan was to use a direct 24 volts input and see what happens. Nothing as it turns out, still defunkt!

Back to the inverter for now.

This fridge has a history of problems on 12v from polyfuses to failed circuit boards. Fridges/coolboxes running off a leisure battery are generally a no-no unless incredibly efficient. THREE times I've had to jump start newbies at events who assumed their battery would keep up with even a tiny coolbox. In this instance this unit clearly needs repairs but it may be uneconomical to bother.