12v Lighting & Batteries

[Scrums]

I wonder if anyone who's good at maths/science or possibly has a bright 14 year old son/daughter could work this out for me:

2 x 20 watt Halogen bulbs (12 volt) How long will they run off a fully charged 85 amp/hour car battery?

Chris.

 

[Woody Alan]

2 x 20 watt Halogen bulbs (12 volt) How long will they run off a fully charged 85 amp/hour car battery?

2x20=40 40/12=3.33Amps 85/3.33=25.75hours

However if you run it for that long to flat, you will possibly destroy the battery even if it is a deep cycle leisure battery. I would suggest 16-20 hours before a recharge.

Alan

 

[Fecn]

Lead acid batteries die very very quickly if you discharge them below 50% - It makes the lead fall off the plates inside. Deep-cycle batteries have thicker lead plates so they can stand being discharged more often. You shouldn't let a 12V lead-acid battery get below about 10.8V.

 

[RogerS]

Old thread, I know, but I remember reading somewhere here (although Search yields nothing...using the wrong search terms probably) that you could sometimes rejuvenate a lead-acid battery by flashing the contacts from a larger battery? Something about whiskers between the plates being blown away? I know it sounds potentially dangerous but...

 

[AndyT]

I don't know the answer but I think the question might give a clue as to why there are specialist companies who supply batteries, maintain them, recycle scrap ones and generally do this technical stuff, safely!

 

[Woody Alan]

The reference to quick flashing a battery is to revive Nicads using a 12v battery. The reason nicads can fail is a short across the plates with large crystal growth, it can be flashed off using this technique. I would not advise such a thing with a lead acid battery. I also never found the flashing a Nicad very successful.

Cheers Alan

 

[RogerS]

Thanks Alan. I clearly got my battery technology confused! It's the recycle bin then.

 

[bosshogg]

Thanks Alan. I clearly got my battery technology confused! It's the recycle bin then.

Actually, you both got it right up to a certain extent. Pulse charging (flashing or sometimes called burp when it's negative or reverse charge) are all claimed to be capable of both boosting discharges and prolonging life, both to Ni-Cd and lead acid. If you care to look at the battery universities pages you can get a better handle on all of thishttp://batteryuniversity.com/
cheers...bosshogg