No more flat battries from your cool-box, TV, lights, etc?

Griffalo · Post by **Griffalo** » Wed May 23, 2007 8:26 pm

I saw this today on the Maplin web site -

http://www.maplin.co.uk/module.aspx?Mod ... y=23m5#buy

Will this put an end to me worrying about leaving the cool box running overnight and the Bongo's battery being flat in the morning?

Is it really this simple?

Darryl

alphabetter · Post by **alphabetter** » Wed May 23, 2007 8:44 pm

I think this is a useful gadget but:

1) A lot of cool boxes have this function built in anyway

2) I personally would feel nervous about deliberately running my starter battery low. Fine to use them as a fail-safe "in case I forget" thing, but I wouldn't want to rely on them as normal operation.

Griffalo · Post by **Griffalo** » Wed May 23, 2007 8:50 pm

My point was that I didn't want to run my battery flat and thought that having one of these would stop that happening.

daveblueozzie · Post by **daveblueozzie** » Wed May 23, 2007 8:56 pm

I suppose it allows you to plug something into it and then cuts off if overused,, for a fiver sounds ok.

alphabetter · Post by **alphabetter** » Wed May 23, 2007 8:56 pm

Griffalo wrote:My point was that I didn't want to run my battery flat and thought that having one of these would stop that happening.

Yes indeed - it should stop the battery running flat, but you are still running the battery to quite a low level so if you have a problem starting you are going to have less reserve battery capacity to help you out.

moonshine · Post by **moonshine** » Wed May 23, 2007 10:25 pm

All these gadgets are fine in theory, but just how low is too low? Battery condition and vehicle condition vary from vehicle to vehicle, and a battery that would start one vehicle at a fairly low state of charge, wouldn't start another. The best way to prevent your starter battery being drained too low for starting is not to run anything off it while the engine is stopped. That is the only sure way of getting started in the morning. If you don't want to have to remember to turn off your coolbox when you switch off the engine, run it from an ignition controlled source.

If you need to run things while stopped, fit a leisure battery. This will be charged while you are motoring, but will be isolated from the starter battery via the split-charge relay while you are stopped.

haydn callow · Post by **haydn callow** » Wed May 23, 2007 10:44 pm

Remember when your battery reads 12volts it is to all intents and purposes FLAT.

Griffalo · Post by **Griffalo** » Wed May 23, 2007 10:52 pm

One day I do hope to fit a leisure battery but they cost a little more than £5.

In the mean time will this not give me a bit of security when I want to keep the milk / water / beers cool while camping, down the beach , out for the day, etc?

Can anyone guess, or does anyone know how long a cool box could run for before the battery (assuming it was fully charged) would drop below 11.2volts?

Darryl

dp bradford · Post by **dp bradford** » Thu May 24, 2007 12:00 am

I reckon this would be a good gadget to protect you from over discharging a leisure battery, but I wouldn't want to have my main battery discharged to 11.2 volts and be confident it would reliably start the engine.

haydn callow · Post by **haydn callow** » Thu May 24, 2007 7:21 am

Running a battery down to 11.2 volts would damage it.

moonshine · Post by **moonshine** » Thu May 24, 2007 8:58 am

Hi Griffalo,

I would not trust one of those devices, except (as dp bradford says) on a leisure battery. A cool box can drain a battery in just a few hours. If your battery is past its best, just a couple of hours could render it useless for starting the engine.

A much better bet for keeping milk, water, beers etc cool would be a well insulated box with ice packs. There are products on the market which are supposedly excellent for this, and they have been mentioned before on here, but my memory is not what it was. Perhaps someone on here will remember though?

patnben · Post by **patnben** » Thu May 24, 2007 9:36 am

Battery terminal voltage is a very poor indication of it's ability
to produce sufficient cranking current to start the engine.

The best you can do with a voltmeter is to test the voltage first
thing in the morning after the battery has settled and measure the
terminal voltage with no load.

A healthy fully charged battery should read 12.6 volts, a completely
discharged battery will read 12.2 volts and will only be capable of
delivering very little current.

As Haydn says above, trying to crank an engine with less than about
12.4 volts open circuit voltage will inevitably damage the battery.

If you intend to use these voltage sensing devices to ensure you
don't deplete your main battery, then I would suggest you carry a
decent set of jump leads on your van at all times.

Griffalo · Post by **Griffalo** » Thu May 24, 2007 1:07 pm

Thanks for all your advice - perhaps I will put the £5 towards some extra freezer blocks / chillerz sheets and only plug in the box while on the move.

Darryl

wrster · Post by **wrster** » Thu May 24, 2007 3:04 pm

patnben wrote:A healthy fully charged battery should read 12.6 volts, a completely
discharged battery will read 12.2 volts and will only be capable of
delivering very little current.

As Haydn says above, trying to crank an engine with less than about
12.4 volts open circuit voltage will inevitably damage the battery.

12.2v is not even near fully discharged, I think perhaps you've got your numbers mixed up. 12.2 is around 50% charged and more than enough to start the engine. Have a look here for a fuller description of voltage/capacity, bearing in mind a battery need to rest before being tested in this manner. Battery capacity by voltage its the last test in the list.

phedders · Post by **phedders** » Thu May 24, 2007 3:54 pm

haydn callow wrote:Running a battery down to 11.2 volts would damage it.

It all depends on the load and the battery condition...