impedance between battery cables w/o battery

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rtlewis
Posts: 2
Joined: Sat Jun 13, 2015 4:36 pm

impedance between battery cables w/o battery

Unread post by rtlewis » Sat Jun 13, 2015 4:51 pm

I have a 97 Isuzu rodeo. I haven't started it since April. I went to start it and it was dead.
A year ago I replaced the battery with an Interstate battery. I had the battery replaced at
no charge. I checked the impedance between the battery cables before I went to connect them
to the battery and I found it to be 10 ohms. I suspect that when the rodeo is turned off, power is
still required by some electronic circuits which usually have an impedance in the 10 to 100 K ohms
given a trickle discharge of maybe 1.2 milli amps down to 120 micro amps. Ohms law tells me that 12v/10ohms = 1.2 amps.
Isn't this high? What should the disconnected impedance be between the cables?

thanks.

 

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carriedi
Posts: 2267
Joined: Wed Apr 10, 2013 12:42 pm
Location: Oregon

Re: impedance between battery cables w/o battery

Unread post by carriedi » Sun Jun 14, 2015 1:38 am

the amp draw will vary depending on what circuits are kept alive and what circuits are put to sleep by the computers in the vehicle. You should look at the actual amp draw after everything is off for an hour. 97 Rodeo may not have a lot of things that stay on but it probably has some.

You should measure the amp draw as soon as you take the key out and close the doors. then watch the draw as time passes. After 45 min to an hour it should be below 0.03 amps

if you aren't going to use the vehicle over months at a time you should probably hook up a battery tender or disconnect the battery because they will go dead over time. Even without a draw, batteries will go dead over time.

rtlewis
Posts: 2
Joined: Sat Jun 13, 2015 4:36 pm

Re: impedance between battery cables w/o battery

Unread post by rtlewis » Sun Jun 14, 2015 8:51 am

Thanks! I was concerned about connecting the
battery to the leads with only 10 ohms resistance
between them and getting a 1 amp spark when I connect the
second lead to the battery. I'll go ahead and connect the battery
and check the amp draw as you recommended. I
appreciate the advice!

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