Charging Small Batteries

Submitted: Thursday, Jun 10, 2004 at 20:07
ThreadID: 13669 Views:1783 Replies:7 FollowUps:1
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Hi all, I have obtained from work two small batteries that were in the phone system. They are 12 v 7.5 amp sealed batteries, it says that they are rechargeable. I have set them up to be camp lights with the low voltage lights that you find as down lights inside houses. My question is how can I charge these batteries when travelling. Can I plug them straight into a cigarette lighter? Will this damage the batteries? How long can I expect out of them with a 50 watt globe??

Cheers and thanks for the advise.

Red Patrol
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Reply By: Jimbo - Thursday, Jun 10, 2004 at 20:30

Thursday, Jun 10, 2004 at 20:30
Your average cig socket puts out about 10 amps and they can draw from that. Most batts will only accept a small charge, certainly won't harm them.

As far as using those 50 watt globes go, watts is a simple mathematical calculation and it is: volts times amps equals watts. That is to say a 50 watt globe draws a little over 4 amps. Given that you should not drain a batt to less than 50% of its capacity you have less than 4 amps useable capacity from each batt, ie under an hour per batt.

Fling the 50 watt globe and get a fluorescent light. Thay come in varying qualities and current drain. They start at about $15 at supercheap for a 13 watt job (drawing about 1 amp) and then get up to something like a versalite which may cost up to $85 and throws a lot more light for the given current draw.

Out in the darkness of the bush acheap fluoro will throw an amazing amoumt of useable light.

I would suggest trying a cheapie and see how you go, but 50 watts is not viable under any circumstances.

Good luck.

AnswerID: 62685

Reply By: GOB & denny vic member - Thursday, Jun 10, 2004 at 20:39

Thursday, Jun 10, 2004 at 20:39
just get some garedn type lights you can get them in 5 &10 watt types
AnswerID: 62687

Reply By: Oskar - Thursday, Jun 10, 2004 at 20:51

Thursday, Jun 10, 2004 at 20:51
I have a 12.5AH sealed battery ($40 from Supercheap) that I use for a tent light but I only use one 20W lamp not a 50. (I use a 20W-12V desklamp type bulb and reflector)
If you link the 2 in parallel you will theoretically get 15AH.
Jim is quite correct in his calculations but with a 20W bulb with the 2 in parallel you might get about 5 hours or so and still be OK.
I have used my little setup for years as its very handy to plonk in the dome tent when I don't feel like running wires from the car, if the car is just that bit further away, or I don't want to leave the ignition switch on accessories overnight.
It's quite handy as a secondary camping light if we want to read for a while etc.

I just plug it into the cig lighter socket for recharging on the road the next day.
(It's also useful in blackouts in the home)
AnswerID: 62690

Reply By: Magnus - Thursday, Jun 10, 2004 at 20:54

Thursday, Jun 10, 2004 at 20:54

Up till last month I used 4 of those batteries wired together to give me a theoretical capacity of 30 amo hours for running my camper lights. Recharge was via a 20 watt solar panel. Lighting in use was 16 watt fluros and 18 watt festoon bulb light for reeading in bed, recently replaced with a 10 watt halogen lamp from Whitworths.

Just replaced the batteries as they had reached the mid point of their stated 3-5 year life and were starting to not hold charge. Now have a 70 amp hour Delkor sealed deep cycle battery.

Go look at the Panasonic web site (google search) That site has excellent data on these 12 v 7.5 amp hour batteries.

I camped for 10 days at a stretch just using the solar panel to recharge during the day. At home put them on a small charge and maintain charger that is used on Motorcycles.

They are a robust battery. Retail for betweem $30 and $45 depending on where you go. The 12 volt specialists, Springers seem to havr the lowest price.

Have fun

AnswerID: 62691

Reply By: joc45 - Thursday, Jun 10, 2004 at 22:03

Thursday, Jun 10, 2004 at 22:03
Hi Red,
These will work fine, with just a few provisos;
- a 50w globe will draw about 4A from your battery, which is less than 2 hours operation from a 7.5ah battery. In practice, you will get much less, since the 7.5ah is (usually) rated at the 20hour rate; ie, 0.375A over 20 hours.
- You should not fully discharge the battery, or you will most likely kill it, so don't run it down till the lights are red/dim, as you will have gone too far. 11v would be your lower limit.
- The sealed batteries, depending on the type, may not like being overcharged, and this may include charging at over 14v from your cig lighter. There are proper sealed lead acid (SLA) chargers available (eg, from Jaycar) but you may have trouble getting one to run off 12v. If you can find one which runs off a plug pack, this may be suitable, depending on its input voltage (ok if around 12v). To recude the risk over overcharging, a simple voltage reducer would be to put a cheap 3A silicon diode in series with the battery if you are charging off the cig lighter. This will reduce the charge voltage by about 0.8v.
Suggest you run lower current-draw lights, such as flouros, drawing an amp or less and leave the 50 globes for your car battery.
cheers, Gerry
AnswerID: 62714

Reply By: Member - Roachie- Thursday, Jun 10, 2004 at 22:08

Thursday, Jun 10, 2004 at 22:08
G'day Red,
I have one of those little suckers for running the 11w flouro around the camp fire when I can't get the truck close enough (those BLOODY green coppers logs!!!).
Anyway, the light usually runs for about 4 hours of the one batt.
As for charging, mine came in a nifty little bag with a female cigi socket (to plug the light into) and also a short cord (about 18") with a male cigi plug on both ends. I just plug one into a socket in the back and the other into the little batt and she's all charged ready for the next night.

AnswerID: 62717

Follow Up By: Red Patrol - Friday, Jun 11, 2004 at 08:39

Friday, Jun 11, 2004 at 08:39
Cheer all, thanks for the fine advise. I will go back to K mart and buy one of those 10 watt halogen globes, a cheap torch and some bulldog clips and wire it all together. It should do the job. I allready have a double fluoro lamp so I should be lit up like a small town. Maybe I'll see you up Tiboburra Innaminka way in the Vic School Hols.

FollowupID: 324046

Reply By: Mad Dog (Victoria) - Sunday, Jun 13, 2004 at 20:46

Sunday, Jun 13, 2004 at 20:46
Good question Red Patrol. For battery longevity you don't really want to charge at more than 1 amp. Plugging directly into the cig lighter with a depleted battery will draw more than this and then continue putting about 14.4 volts across the batt when fully charged which aint good. Not sure of the answer yet I'm still deciding my options as I'm going through the same thing myself. One option is the 240 volt sla charger plugpack from dse running from an invertor this is a 3 step charger that can be left connected continously. Another option is the 12v charger regulator kit also from dse. this will still put an over ideal rate of charge into the battery though. The other option is just plug the thing in and guess how long it needs to remain on charge but you can end up with either under or overcharge.
AnswerID: 63022

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