Jump starting a flat battery.

We have all done it at some stage, left the fridge running, headlights on resulting in a dead battery.
Hook it up to a charger and it does not charge. Using another charged battery and jumper leads the flat battery can be jumped to commence recharging.
As mentioned in another post, we have been buying dead batteries for a few $"s from recyclers and jumping them for our bush camp. (Some last years.)

Could one of the auto gurus here explain how/why it is possible to jumpstart/recharge a dead flat battery?
It definitely works but do not know the technicalities?

I would like to know the answer to this too. I don't know why that would be unless a fully charged battery is like a slap in the face of the dead one to wake it up compared to a charger with built in protections for the cars electronics that try to give it a gentle massage. You can tell I know alot about electrical stuff hey layful:

I've read:
You're likely using a smart charger.
Most of the new intelligent chargers need to see a voltage on the battery before they will start up.
This is a safety issue, to prevent the charger from arcing when the electrodes are shorted.
If the battery voltage is so low that the charger can't detect it, the charger won't turn on. In this case you need to bootstrap the battery by jumping it to another battery to get a small bit of charge in it.

Is it a stage charger?
If it is they don't seem to see the low voltage, and won't kick in. But it will recognise voltage from the other battery to get it going.
Prob only needs 3 to 5 seconds of volts to get it going from the jumper battery.
You shouldn't have a problem with the old type of charger.

Ha, must of been writing at the same time bigwave! :lol:

Big brother watching our every word!

Definitely not a new charger, one of the old 6/12 volt types, we hit on this by chance in the early 90's. However yes, once the charger kicks in we disconnect the jump battery after about 5 minutes and leave the dead one charging overnight.
The batteries we select from the recycler are only a few years old and either completely dead or only registering a few volts. One battery in particular was a wheat silo type shape. This battery when restored started our camp diesel generator for another 6 years. The generator has an inbuit trickle charger.

How many amps max out is there?

Put yur multi meter on 20v.
Black on earth terminal,
Start by dipping your probe in each cell.
Yes, Into the acid.
Measure each cell back to earth then do the same from the positive side.

If each cell comes up with the same voltage,
You will be able to recover it.
If one drops right out, You either have a shorted
or completely dead cell.
May explode or do nothing.

Reason why is the plates have formed a sulphate crust over them and will not conduct.

A transformer charger of about 4 amps for a week will work.

I have just recovered a battery of mine by putting some
epson salts disolved in warmed demineralised water and
trickle charging for a week.

This applies for lead acid batteries only.

If you do not know the dangers involved with this type of battery,
Please do not go there.

Good tip, Tathradj!
Can I give another little tip??
After measuring individual cell voltage in the manner described above, make sure you thoroughly rinse the red probe of your multi meter!!
Because otherwise... you will come up with another little tip!!

Just lick it! Good for getting nicotine stains off your teeth :lol:

Thanks for the tip Tathradj, with your multi meter method.
You mention the cells bridging out. Another method we use to keep the batteries holding a charge is. we give the battery a good shake, remove the plugs and tip it up side down in a plastic tub. Put the tub of electrolyte to one side to let the crusty bit settle. Flush out the battery with hose water and let it drain.
Finally using a bulb battery tester carefully suck up the acid and refill the battery leaving the crusty bits behind.
Crank up the genny, hook up the battery charger again and give it a charge.
This doesn't always work but it may keep our lights shining until we head home and bring a couple more batteries back with us next trip.

One thing we haven't tried is whether you can do the "jump starter" trick with a solar panel and regulator?

Simmo, Just straying from subject for a question. Feel sure you can explain something that I've wondered about?
I see you handle a rifle left handed, I'm left handed but had to learn to shoot right handed.
How do you NOT get and earful of empty shells when firing an automatic?

Nightjar said:

Simmo, Just straying from subject for a question. Feel sure you can explain something that I've wondered about?
I see you handle a rifle left handed, I'm left handed but had to learn to shoot right handed.
How do you NOT get and earful of empty shells when firing an automatic?

Click to expand...

Pretty sure it is a gel blaster Pete, no cases.

Cheers

Doug

Nightjar said:

Simmo, Just straying from subject for a question. Feel sure you can explain something that I've wondered about?
I see you handle a rifle left handed, I'm left handed but had to learn to shoot right handed.
How do you NOT get and earful of empty shells when firing an automatic?

Click to expand...

Well spotted sir!!
(And yeah Doug, its an M4 Gelblaster!)

Nightjar, when I was in the RN, exactly that would happen!
My forearm would get hit by the ejecting shells and I would end up with a burn on my arm!
But hanging onto a .308, a little arm discomfort was the last of my worries!!

Yeah, what is the go there if I may ask about your avatar Simmo.
The beard and uniform conflict a bit.....
Is that just taken at a rifle range ?
Did you ever serve?

mudgee hunter said:

Yeah, what is the go there if I may ask about your avatar Simmo.
The beard and uniform conflict a bit.....
Is that just taken at a rifle range ?
Did you ever serve?

Click to expand...

The post #15 above answers eh??

Dont worry Simmo....hes having a crack at me.

Some interesting stuff on Finders. Yuck!

Reg Wilson said:

Some interesting stuff on Finders. Yuck!

Click to expand...

WTF! If that's true - good riddance