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Author Topic: I have 12v at battery but only getting 2 to 5 volts at my panel.  (Read 2492 times)
jjchristian84
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1953 GMC PD 4104-008




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« on: April 30, 2013, 01:55:31 PM »

I left my on switch on my 4104 and killed my batteries. I tried jumping it with van and the first time I cranked it it turned like it was trying to start, but didn't have enough juice. So I left it to charge for a little while. When I came back I flipped the on switch but didn't hear any of my relays click and no starting action going on. I pulled out my meter and it read about 5.5v at the panel. I checked the batteries and they are at 12.63v. Left it to charge for a little while longer hoping it would work it's self out. I came back and flipped the master switch and heard the relays click. But hit the starter switch and nothing happen. Checked the panel again and this time it is at about 2v. Any idea what is going on here?
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Frank @ TX
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« Reply #1 on: April 30, 2013, 03:40:14 PM »

Hi jjchristian84,
Someplace between the battery and the dash there is a loose connection.
Keep checking the voltage alone the way and you'll find it.
Look at both the pos and neg lines.
Good luck
Frank
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jjchristian84
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« Reply #2 on: April 30, 2013, 04:35:59 PM »

Thanks. I think my Master Diesel Relay is bad. I went to dinner and checked it again when I got back. It is now at 12 volts again, but I didn't try starting it again yet. Maybe some bad grounds causing the relay to overheat. Not sure. Just have to keep checking I guess.
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gus
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« Reply #3 on: April 30, 2013, 06:52:07 PM »

As I remember there are at least two relays necessary to start a 4104, probably more.

Your batts are probably just too weak and volts too low. You also may have one batt shorted, check each separately with a load tester after charging each separately. A shorted batt will kill the other, been there. 12.63v is not proof the batt is good, only a load tester will tell you for sure. $25 at WM.

Leaving the engine run switch on kept a couple of relays activated which drew down the batts.

How did you leave it on and shut down the engine? Or are you talking about the elect master switch?
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PD4107-152
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Jnbroadbent
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« Reply #4 on: April 30, 2013, 07:06:41 PM »

As I remember there are at least two relays necessary to start a 4104, probably more.

Your batts are probably just too weak and volts too low. You also may have one batt shorted, check each separately with a load tester after charging each separately. A shorted batt will kill the other, been there. 12.63v is not proof the batt is good, only a load tester will tell you for sure. $25 at WM.

Leaving the engine run switch on kept a couple of relays activated which drew down the batts.

How did you leave it on and shut down the engine? Or are you talking about the elect master switch?

You can get it load tested at a discount auto for free fwiw
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Jon
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jjchristian84
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« Reply #5 on: May 01, 2013, 05:51:44 AM »

Yeah, I left the master switch on. So the batteries may be toast? I just bought new ones. That would be a disappointment.
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Jeremy
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« Reply #6 on: May 01, 2013, 08:48:25 AM »

Flattening the batteries will hurt them, but it shouldn't kill them, especially if they weren't left flat for very long. When they were flat, were they totally flat (ie., 0v)? If so that certainly isn't good and it can often be difficult to get batteries in that state to start to charge again - but it sounds like that wasn't a problem in your case, which may be a good sign.

As has been said, a load tester will determine whether your re-charged batteries actually still have a capacity. Failing that, simply measuring the voltage at the battery with your existing meter, but whilst trying to crank, will probably tell you what you need to know.

Jeremy


Edit: It occurs to me that I'm not clear on whether the 2v at the panel situation is happening all the time, or only when trying to crank. If it's only when trying to crank (and if measuring at the batteries gives the same voltage) then it's probably the batteries at fault. But if it's happening all the time then the problem has got to be in the bus (and presumably anything in the bus wiring which can cause such a large voltage drop when not trying to crank is potentially quite serious, not to say a big permanent drain on the batteries)

« Last Edit: May 01, 2013, 09:03:36 AM by Jeremy » Logged

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gus
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« Reply #7 on: May 01, 2013, 02:24:57 PM »

It takes a while to recharge batts that have been completely discharged, it needs to be done slowly.

A jump start will not work on a completely dead batt, even on a car.

Unless the batts are pretty old I agree with Jeremy that they probably are ok, it just takes patience or renewing their life. However, complete discharge will often kill an old batt.
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jjchristian84
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« Reply #8 on: May 01, 2013, 06:14:15 PM »

They are both new batteries. But I have been forgetful lately and have drained them a couple of times down to 0v. Here is how the voltage problem goes: If I went out right now and measured the batteries they read 12volts +/-. Turn on the master switch, the relays click, and the panel shows 12volts +/-. Hit the starter switch and it gets half a turn before dying out. The battery gauge reads very low, almost negative and now the panel reads 2 to 5 volts. Now, turn the master switch off and back on and the relays do not click and the panel is still at low voltage. Batteries still reading 12 volts though. If I wait five or ten minutes I can go back out there. Flick the master switch, relays click, and do that whole process over again. Never resulting in more than half of a turn on the motor. This still happened while I had two running vehicles hooked up to it with jumper cables.
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Sam 4106
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« Reply #9 on: May 01, 2013, 06:37:48 PM »

Is your 4104 still positive ground? If it is, and you are jumping the batteries from a negative ground vehicle, with the positive jumper cable hooked to the negative bus battery post, you are charging the bus batteries backward. With a completely discharged battery, it can be charged backward and have very little power. I know this is a long shot, but I've seen some really strange things happen. If you have charged the bus batteries backward, they will have to be completely discharged again to try to charge them correctly. If your 4104 has been switched to negative ground, the above doesn't apply.

Good luck, Sam
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Ed Hackenbruch
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« Reply #10 on: May 01, 2013, 07:46:54 PM »

Put the charger on them and leave them for 2 or 3 days before trying to start it,...they might come back if you are lucky. Since you drained them a couple of times, even though they are fairly new, I would start thinking about buying new ones. Take them in and have them load tested before you buy any just to be sure they are shot.
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1968 MCI 5A with 8V71 and Allison MT644 transmission.  Western USA
jjchristian84
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« Reply #11 on: May 02, 2013, 07:08:41 AM »

I can't say I am familiar with the positive/negative ground idea. It had old batteries when I bought it and I was able to jump start it them. So...It has been changed over? I got one new battery yesterday. I'll get the other one in a couple of days. Here's to being hopeful. The limits of my 'handyman'-ness is getting stretched to it's limits!
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Ed Hackenbruch
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« Reply #12 on: May 02, 2013, 09:48:03 AM »

Follow your battery cable from the starter back to the batteries. If it attaches to a + post, you have a negative ground, if it attaches to a - post, you have a positive ground.
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1968 MCI 5A with 8V71 and Allison MT644 transmission.  Western USA
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« Reply #13 on: May 02, 2013, 10:19:04 AM »

Check all the connections you can from the battery to the starter.  Check the grounds also.  It could even be in the cable connectors.
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jjchristian84
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« Reply #14 on: May 02, 2013, 11:52:43 AM »

Thanks! I'll do that.
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