another battery question

[cagey]

hello again
working on my boat today with just radio connected to battery it started to cut out and eventually packed up, connected to next battery ( only had 1 terminal connected) and radio worked fine again.
the battery is 110a fully charged last weekend and the radio had been on approx 15 hours (fri sat and sun) is this normal or does it mean the battery is losing it.
It was only radio 2 nothing too outrageous
thanks
keith

 

[wooslehunter]

Certainly sounds as though you have either a duff battery of a duff charging system.

I've just recharged my 70AH domestic battery as a precaution after lots of hours using the radio.

Let's say just for the sake of arguement that your volume is set so the radio takes 24W - that would actually be pretty loud for just background. With nominally 12v you then have 2A load on the battery. Even if you only get 50% capacity which is a pretty sick battery, you'd still expect it to last 27hrs and thats' with 24W continuous load.

 

[bonny]

If your radio has cut-out because the battery voltage has dropped too far (probably below 10V) then either you've got one stonking big radio or an OAP battery. At 100AH and 15hrs use equates to 7.3A (87W). Most radios should typically draw no more than 2A. This looks as though your battery is only giving around 30AH. You could check your radio consumption if you've got an ammeter.

You don't say how old your battery is, or how it's been treated.
If it's more than 5 years old it's likely to be loosing it but if it's been well treated during it's life I would expect better than this.

If it's been fully discharged for more than a couple of months or the acid level has dropped then it may have sulphated. Sometimes this is partly recoverable but more often than not is terminal. You could try adding some battery pills (avail from most car acc. shops) since they cost only a few quid, but you may well finnish up buying a new battery.

I've used 75-85AH batteries in the past avail fro around £35 from some caravan shops. Good value.

 

[VicMallows]

Agree with others, appears your battery is *really* finished. Your radio won't be taking more than 500mA (half an amp) in receive squelch/standby.

Give us some history to the battery. Even quite new cared-for batteries occaisonally develop one bad cell so that voltage on-load drops to around 10.5v which may not be enough for some radios. If the battery has a 'magic eye' (hydrometer) this only indicates one cell which may well happen to be a good one.

If on a tight budget and need to replace, go for cheap 'caravan' one at around £30.

Vic

 

[William_H]

Hi Cagey I agree with the others except that half an amp and probably far less is a better current expectation for a simple radio. So you need to ensure the battery is fully charged (probably at home)and fluid level is up (if you can check it.) Fully charge by putting about 150 amp hours into it. ie 150 hours at 1 amp or 75 hours at 2 amps etc. You need a charger with an amp meter or a multimeter with amp range. Now connect a light bulb of known wattage ie 6watt bulb draws half amp 18 watt globe draws 1.5 amp 48 watt raws 4 amp. or better still use your multimeter amp range to check actual current being drawn by the lamp. Again multiply the current by the time that you get a reasonable voltage from the battery ie until it reduces below 11.5 volts. This gives you actual useable amp hours which of course is what you want from your battery. if you can get more than half of the rated amp hours out it is OK and not worth replacing but if you only get a tiny fraction of the rated capacity as your radio test indicates then ave a noo one.
Good luck will

 

[oldharry]

You could try adding some battery pills (avail from most car acc. shops) since they cost only a few quid, but you may well finnish up buying a new battery.


Correction: you WILL finish up buying a new battery. So don't waste money on 'pills', they only give a marginal short term boost.

1 of two things wrong to cause the problem:
1: bad connections. You said the radio 'started cutting out' - suggesting it was coming back on again. This would not happen if the battery was going flat. Once off it would have stayed off!

2. An internal fault in the battery - again taking from your description that it was cutting out and returning.

Remedy, before you charge the battery, check the voltage on the terminals. A 100 ah battery even in very very poor condition indeed should still run a radio for a lot longer than 15 hours. If the terminal voltage exceeds 12.5 volts then either the radio or the wiring is up the creek.

Anything much under 12.3 volts then the battery is dead. Assuming it WAS actually fully charged before you started...?

Another test if you want to be sure: Get a 60 watt headlight bulb (preferably not Halogen type as they may burst if you touch them, and run much hotter), and connect wires to the terminals so that you can connect it across your battery.

Fully charge the battery, and check its voltage half an hour after disconnecting the charger. It should be around 12.8 volts. Now connect the light bulb across it and leave it for at least 4 hours. AT 60 watts the notional current drain will be 5 amps, so multiply the number of hours by 5 and you will get the number of AH you have taken out. Let the battery stand 10 or 15 minutes after disconnecting to allow the voltage to stabilise, and check the terminal voltage again. If the start voltage was 12.8, then a good 100 ah battery should still be giving around 12.6 volts, certainly not much under 12.5.

 

[roger]

Why not buy a cheap digital multimeter - they are not expensive and check. It could also be dodgy wiring and this can be checked with the meter too.

 

[brianrunyard]

1. Check the connections.
2. Check battery with hydrometer.
3. "......fully charged last weekend......", How did you check it was fully charged? Check the charger.

 

[Anonymous]

It's not an unheard of fault for a radio to stop working when the volts fall below a certain level still within the normal spec for the battery. Do check before throwing out the battery!