Testing scrapyard car batteries?

Vortex · Post by **Vortex** » 12 Oct 2006, 15:48

I've just bought a couple of 600w 12vDC->240AC invertors.
(Very cheap - ?35 each - Maplin B grade stock)

I now need to buy some used 12V car batteries.

There is a breakers yard about 1 mile away so I might try them.

So .... how will I be able to select /check the 12V batteries to rip out of the blood soaked car wrecks?

Will a voltmeter be enough? Or a 12V bulb on flying leads? Or will I need a special gadget?

Don't forget that these cars are crushed wrecks stacked on metal frames ... VERY hard to access. This means that any test must be quick and easy to do ... I don't want to spend tons of effort to remove batteries only to find that they are duff!

Thanks in advance for any tips!

PS Any idea what I should be paying for these secondhand 12V batteries from the scrapyard, in batches of say 10?

Post by **mikepepler** » 12 Oct 2006, 16:07

Have a look here for detailed info: http://www.batteryuniversity.com/parttwo-41.htm

Putting it simply though, a car battery is empty at 10.5V, and full at 12.72V, assuming it's not plugged into a charger at the time you're measuring. If you find the battery is much below, say, 11V, then there's a strong chance it's knackered - i.e. physically broken inside due to discharging too far. You just need an accurate voltmeter to check it.

simonrichards912 · Post by **simonrichards912** » 12 Oct 2006, 16:08

Surely the scrapyard will be obliged to remove the batteries for recycling to prevent leakage of acid etc?

Vortex · Post by **Vortex** » 12 Oct 2006, 17:56

Thanks guys,

I'll take my trusty DVM along.

Bandidoz · Post by **Bandidoz** » 12 Oct 2006, 20:06

..and don't forget to take a test load.

Vortex · Post by **Vortex** » 12 Oct 2006, 21:31

Bandidoz wrote:..and don't forget to take a test load.

Would a chunky 12v bulb be OK?

Bandidoz · Post by **Bandidoz** » 12 Oct 2006, 21:36

A ballast resistor would be more to the point; a bulb is non-linear.

Cycloloco · Post by **Cycloloco** » 12 Oct 2006, 21:44

simonrichards912 wrote:Surely the scrapyard will be obliged to remove the batteries for recycling to prevent leakage of acid etc?

True, and another factor is that the lead in the batteries is worth more than the same weight of scrap steel. The battery and tyres should be removed from the vehicles and not included in the scrap metal.

What you need is a scrap yard that deals with crashed cars after the insurance assessors have had their say. Those cars' batteries will not be clapped out.

Post by **kenneal - lagger** » 13 Oct 2006, 00:37

Car batteries won't last long even if they are in good nick. They're designed to provide a very high current over a short period of time and don't like being discarged to any depth. You need Deep Cycle batteries, often sold as Leisure batteries. They are designed to discarge to about 20% capacity. When you're working out what power capacity you need work on 50% depth of discharge for safety and extended life.

Post by **mikepepler** » 13 Oct 2006, 07:53

kenneal wrote:Car batteries won't last long even if they are in good nick. They're designed to provide a very high current over a short period of time and don't like being discarged to any depth. You need Deep Cycle batteries, often sold as Leisure batteries. They are designed to discarge to about 20% capacity. When you're working out what power capacity you need work on 50% depth of discharge for safety and extended life.

But if he can get them for free, just to experiment for a few months, then it's not too bad.

I wonder what would be required to disassemble car batteries and rebuild them as deep-cycle? As far as I understand it, the main difference is that the lead plates are thicker and more widely separated, and sometimes are even cylinders rather than flat plates. How hard is it to melt down lead and reform it into a new shape? And how do you get a battery apart without getting acid everywhere, and create a new acid-prooof container for your new battery? Can you avoid poisoning/injuring yourself in the whole process? I'd be interested to know, as one day we might need to actually do this...

Vortex · Post by **Vortex** » 13 Oct 2006, 09:45

What you need is a scrap yard that deals with crashed cars after the insurance assessors have had their say. Those cars' batteries will not be clapped out.

Yes, that's what is is ... lots of nasty "fatals" .... yuk.

Post by **kenneal - lagger** » 13 Oct 2006, 16:09

Experimenting with them would be OK, Mike, as long as Vortex knows that they won't last long. I wouldn't want an experiment to convince someone that batteries don't work.

The recyling system for batteries is quite well set up I think but it might be useful in the future to know how to DIY.

Post by **mikepepler** » 13 Oct 2006, 17:04

kenneal wrote:The recyling system for batteries is quite well set up I think but it might be useful in the future to know how to DIY.

That's what I was thinking, I wondered if anyone had ever experienced breaking a battery open, even if it was by accident!?

Bandidoz · Post by **Bandidoz** » 13 Oct 2006, 17:05

Might be more to the point to experiment with submarine batteries as they were designed to be serviced.

Post by **kenneal - lagger** » 13 Oct 2006, 18:36

They're difficult to get hold of now. If you know where I can get some I would like to add to my set.