[AT] Batteries charged backwards.
szabelski at wildblue.net
szabelski at wildblue.net
Thu Feb 13 17:33:57 PST 2020
You will not drawn the maximum current of the battery. The amount of current you will draw through the resistor is I=V/R, and the power will be as you stated W=V*I. By combining the two equations you will see that W=(V*V)/R.
So, on a 12V battery, you will see 144/R for the power draw.
For a 1 ohm resistor, 144W
For a 10 ohm resistor, 14.4W
For a 100 ohm resistor, 1.44W
And so on, and so on.
I have an old Sears Automotive Analyzer that came with a resistor for testing the charging system. The resistor is a thin wire strip wrapped around a ceramic core. According to the manual it’s only a 1/4 ohm resistor. It doesn’t say what the wattage is, however, it says that you should see 7 to 7.6V on a good 6V charging system, 13.8 to15.4V on a good 12V charging system, and 26 to 29V on a good 24V charging system.
So doing some more math, the current going into a battery from a good charging system would be:
6V system. - 1.16 to 1.26A of current
12V system. - 1.15 to 1.28A of current
24V system. -1.08 to 1.21A of current
Based on 144/R from above, the power rating of the resistor of the analyzer is 576 W. So the rating of any resistor used for testing should be at least 600W or more.
The resistor is mounted on an aluminum block with a shorting link. To use the resistor with the analyzer, you disconnect the positive battery cable, clamp the resistor (with the shorting link closed) to the battery, and then connect the positive battery cable to the resistor. After staring the engine, you open the link and take a current reading on the analyzer.
Carl
----- Original Message -----
From: Dean VP <deanvp at att.net>
To: Antique Tractor Email Discussion Group <at at lists.antique-tractor.com>
Sent: Thu, 13 Feb 2020 17:39:26 -0500 (EST)
Subject: Re: [AT] Batteries charged backwards.
Very few if any load testers that we shade tree mechanics own are capable of being used as a constant load. I know mine can only be used for a few seconds on a fully charged battery or it will over heat. I don't know how many ohms the coil has but I suspect to properly load a 12v battery for a test one would want to draw at least 50 amps momentarily. Power = VxI.... 12 x 50 = 600 watts. That is a lot of watts to dissipate in a small air coil. Possibly short duration loads will eventually draw the battery down.
.
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On Wed, Feb 12, 2020 at 2:08 PM, szabelski at wildblue.net<szabelski at wildblue.net> wrote: When connected in parallel, the current being put through the batteries will
split between the two, with most of the current going through the good
battery and the dead battery only getting a portion of the current. The dead
battery will have a higher internal resistance and will limit the current.
When jumping a dead battery you are limited as to how much current your car
alternator will provide. Your alternator is only rated for so mush output
and your running car is using some of that. That’s why it sometimes help to
turn off all lights, radio, etc. on the running vehicle when jumping a
really dead battery. It’s also good the turn off all the lights, radio, etc
on the dead vehicle so that whatever your providing is going to go to the
battery and starter of the dead vehicle. Sometimes people will rev the
engine thinking that they’re getting significantly more lower out of the
alternator (double??). This is not the case, you are limited.
When your vehicle is running, the alternator puts out about 14V after a
start, then, once the battery is charged back up, the output should drop to
12V for running whatever is turned on. At that point your battery is
basically in idle mode, unless the alternator can’t carry the total load,
then it tries to make up the difference.
Carl
Carl
----- Original Message -----
From: Thomas Martin <tmartin at xtra.co.nz>
To: Antique Tractor Email Discussion Group <at at lists.antique-tractor.com>
Sent: Wed, 12 Feb 2020 14:47:29 -0500 (EST)
Subject: Re: [AT] Batteries charged backwards.
Stephen
Well it appears you do not understand the difference between connecting in
series and parallel.
When you jump start a vehicle, one connects in parallel, the current from
the jumper battery does
not have any affect on the the dead battery.
Tom.
> On 13 February 2020 at 07:52 Stephen Offiler <soffiler at gmail.com> wrote:
>
> I wouldn't purposely put 50 amps into a totally dead battery if I
> didn't have to, but then we have the example cited by others, the
> jump-start. Who-knows how many amps will flow; limited only by the
> internal resistance of the batteries and the cables & connections. I
> don't think many people appreciate that a jump-start is actually sort of a
> hail-Mary maneuver. If you didn't need to get the car/truck/tractor
> started ASAP, the smart move is to charge the battery slowly and
> correctly. People are going to chime in and say "I've been jump-starting
> my entire life and never had a problem!" OK. Me too. But the issue here
> is that it's impossible to know how much you might have shortened the life
> of that battery by hitting it with that big uncontrolled amperage surge.
> In Cecil Bearden's case, he's not stuck in a field or a parking lot or
> whatever. He has the opportunity to do it right. And that definitely does
> NOT include hitting it with a giant surge.
>
> SO
>
>
> On Wed, Feb 12, 2020 at 1:08 PM Thomas Martin < tmartin at xtra.co.nz
> mailto:tmartin at xtra.co.nz > wrote:
>
> > >
> > Surely US battery chargers have adjustable amperage?
> >
> > I thought it was a given that you wouldn't put 50 amps into a
> > dead battery...
> >
> > Tom
> >
> > > > > On 13 February 2020 at 03:14 Stephen Offiler <
> > soffiler at gmail.com mailto:soffiler at gmail.com > wrote:
> > >
> > > Hold on. A completely dead 12V battery connected to a
> > > good 12V battery is going to cause very large current to flow into the
> > > dead one. This is not a good idea.
> > >
> > > SO
> > >
> > >
> > > On Wed, Feb 12, 2020 at 9:08 AM < szabelski at wildblue.net
> > > mailto:szabelski at wildblue.net > wrote:
> > >
> > > > > > > Cecil,
> > > >
> > > > I agree with completely discharging the batteries
> > > > and then putting the batteries in parallel one at a time with a good
> > > > 12V battery. The batteries will try to equalize when in parallel.
> > > > When you drain the battery, take the load off and let the battery
> > > > sit for a while, then put the load back on and drain some more.
> > > >
> > > > You should use a battery charger that has a trickle
> > > > charge feature. This puts a full charge into the battery at first,
> > > > then drops down to a small charge to top the battery off. You may
> > > > have to do this several times and should leave the charger on for at
> > > > least one full day. Don’t rush the job.
> > > >
> > > > You can also check that each cell is good by taking
> > > > a reading between each cell. A bad cell will indicate a lower charge
> > > > then the others. Do this with every recharge attempt and note if you’re
> > > > making any progress.
> > > >
> > > > Don’t know if you’ve ever gone on-line to look for
> > > > videos on bringing dead batteries back to life, but their are some
> > > > that show how to drain a battery, rinse it out, then refill and
> > > > recharge. They appear to work out quite well, but I can’t swear by
> > > > them since I’ve never done anything like this myself.
> > > >
> > > > Good luck!
> > > >
> > > > Carl
> > > > ----- Original Message -----
> > > > From: Thomas Martin < tmartin at xtra.co.nz
> > > > mailto:tmartin at xtra.co.nz >
> > > > To: Antique Tractor Email Discussion Group <
> > > > at at lists.antique-tractor.com mailto:at at lists.antique-tractor.com >
> > > > Sent: Wed, 12 Feb 2020 00:24:36 -0500 (EST)
> > > > Subject: Re: [AT] Batteries charged backwards.
> > > >
> > > > Hi Cecil
> > > > I consulted a very good friend on the other-side of
> > > > the isle.
> > > > Tony is auto-electrician, of vast car, truck &
> > > > tractor experience.
> > > > He says you MUST discharge the batteries, separately
> > > > with a bulb.
> > > > They need to completely discharged. No measurable
> > > > voltage.
> > > > Then one battery at a time needs to be placed in
> > > > parallel with another
> > > > fully charged 12v battery, they then need to be
> > > > connected to a 12v
> > > > charger...
> > > >
> > > > Tom
> > > >
> > > > > On 12 February 2020 at 15:31 Cecil Bearden <
> > > > crbearden at copper.net mailto:crbearden at copper.net > wrote:
> > > > >
> > > > >
> > > > >
> > > > > > I had 2 group 31 batteries out of the tractor
> > > > that were completely
> > > > > > dead. I hooked them up in series and connected
> > > > my 24Vcharger to them
> > > > > > as It was handy and I wanted to charge both.
> > > > After a couple of days I
> > > > > > checked them and found that I had hooked the
> > > > charger backwards. I
> > > > > > hooked a couple of incandescent headlights to
> > > > drain the battery, but
> > > > > > after 3 days they won't light up the headlights,
> > > > but they still have a
> > > > > > lot of spark when shorted with cables.. A guy
> > > > at my battery shop said
> > > > > > I should hook up a 6volt light to them and use
> > > > that to run them
> > > > > > down.... At $100/ea, I need to try to save
> > > > these...
> > > > > > Cecil
> > > > > _______________________________________________
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