Batteries Deplete:

[Rob]

I arrived back at my shop after being gone for a month and three trucks with 12 volt 40MT starters have batteries that will not start their respective units. They are not completely flat, but appreciably low so with a boost all roared back to life. My old "Yellow Dog" with a series/parallel switch fired right up. All batteries are group 31 and and are verified good by testing. There is also 1/2-3/4 ampere draw through the circuit any time the batteries are connected to the starter solenoids. This is consistent through all units. Battery cutoff switches could be installed but I'd rather have the problem corrected.

I don't know if this is a common occurance or not. I plan to ask my electrical rebuilder today. I've seen starter draw through the windings due to corrosion but don't know if some units are more suseptable to this or not. None of these trucks have any ancillary equipment installed to cause parasitic losses.

Rob

[Bollweevil]

I arrived back at my shop after being gone for a month and three trucks with 12 volt 40MT starters have batteries that will not start their respective units. They are not completely flat, but appreciably low so with a boost all roared back to life. My old "Yellow Dog" with a series/parallel switch fired right up. All batteries are group 31 and and are verified good by testing. There is also 1/2-3/4 ampere draw through the circuit any time the batteries are connected to the starter solenoids. This is consistent through all units. Battery cutoff switches could be installed but I'd rather have the problem corrected.

I don't know if this is a common occurance or not. I plan to ask my electrical rebuilder today. I've seen starter draw through the windings due to corrosion but don't know if some units are more suseptable to this or not. None of these trucks have any ancillary equipment installed to cause parasitic losses.

Rob

You probably have already disconnected the alternator, and the main accessory feed cable from the solenoid before testing. Having 4 different units with the same problem is puzzling. Let me know what you find, and I will fix mine. I will send you a new 42 MT solenoid for

a test unit if you like. You could ground it to the engine and see if it makes any difference.

[Rob]

You probably have already disconnected the alternator, and the main accessory feed cable from the solenoid before testing. Having 4 different units with the same problem is puzzling. Let me know what you find, and I will fix mine. I will send you a new 42 MT solenoid for

a test unit if you like. You could ground it to the engine and see if it makes any difference.

Hi James, yes before I left this last time I ensured all batteries were up to full charge and left two trucks with the alternator, and auxilary wiring to the solenoids disconnected. This rules out all but the starter solenoid wiring and contact(s) internal to the units. There was only the positive battery cable(s) left attached.

I seem to remember the 42MT starter solenoid being different that the 40MT series but I have a couple new ones in my stowage room to fit these. I did talk to the folks that rebuild starters for me and they say it is fairly commonplace for them to burn and arc the copper ring and draw minute amounts of current through the circuit that should be completly open.

I'm going to pull a starter this evening and see what gives.

Thanks,

Rob

[Rob]

You probably have already disconnected the alternator, and the main accessory feed cable from the solenoid before testing. Having 4 different units with the same problem is puzzling. Let me know what you find, and I will fix mine. I will send you a new 42 MT solenoid for

a test unit if you like. You could ground it to the engine and see if it makes any difference.

Pulled the battery cables from the starter tonight on my 73 RL and put a multimeter from the terminal where the battery cables mount and the engine block, then the starter housing. I measure a varying 3900-4200 ohms when there should be an infinite open. This truck has not spent a single night outside since I've had it nor has it ever been rained on in that timeframe. The problem shouldn't be moisture related. It's too damned hot to do anything with it right now so I'll pull the starter later this evening to replace the solenoid. I also metered the new one and there is no conductivity inside.

Rob

[theakerstwo]

3900- 4200 ohoms is same as open. It would take a long time to draw down the battiers at that.I think a voltometer in t56he dash will draw some but not enough to draw battiers.The starter motor has no voltage to it untill selnold engagement and the only way a selnold can draw would be deposits build up inside on the contacs. On 31 battiers if you have one dead it will pull the others over time. Process of elimination is what you will have to do. Rob you talking about electric coils reminded me later about a instructor years ago that i had could take both hand and grab all 6 wires in a little engine and kill it. I had forgot about it but i remenber him showing us for some reason and he was our automotive electric instructor.

[Bollweevil]

3900- 4200 ohoms is same as open. It would take a long time to draw down the battiers at that.I think a voltometer in t56he dash will draw some but not enough to draw battiers.The starter motor has no voltage to it untill selnold engagement and the only way a selnold can draw would be deposits build up inside on the contacs. On 31 battiers if you have one dead it will pull the others over time. Process of elimination is what you will have to do. Rob you talking about electric coils reminded me later about a instructor years ago that i had could take both hand and grab all 6 wires in a little engine and kill it. I had forgot about it but i remenber him showing us for some reason and he was our automotive electric instructor.

I once worked in a Chevrolet dealership, One of the fellow's I worked with would pull the coil wire from the distributor of a chevy 6 cylinder engine, hold the wire contact against his palm with his little finger, stick his thumb against the distributor cap, and have someone start the engine. I never tried it myself. I can't stand getting bitten by accident.

[Rob]

3900- 4200 ohoms is same as open. It would take a long time to draw down the battiers at that.I think a voltometer in t56he dash will draw some but not enough to draw battiers.The starter motor has no voltage to it untill selnold engagement and the only way a selnold can draw would be deposits build up inside on the contacs. On 31 battiers if you have one dead it will pull the others over time. Process of elimination is what you will have to do. Rob you talking about electric coils reminded me later about a instructor years ago that i had could take both hand and grab all 6 wires in a little engine and kill it. I had forgot about it but i remenber him showing us for some reason and he was our automotive electric instructor.

Agree with you Glenn as the current draw is only about 600ma; That is not much but the truck set for about a month without being touched by anyone. These batteries have no dead, or weak cells that I could tell with both a temp compensated hydrometer, and internal cell resistance meter. All cells read very close and linear to each other. I did pull the starter assembly and removed the solenoid. It's internal resistance is the same removed from the starter motor between the battery connection post and the starter motor post. The starter motor windings are near a dead short from the post to the case. I haven't taken the solenoid apart yet to flip the ring or replace the contacts, but will probably get to that tomorrow. Someplace around here I've got a few of those parts......

I've seen that trick with killing a running small engine. Never tried it myself. It's always been with a distributor type ignition, never a magneto.

Thanks,

Rob

[Mike]

Agree with you Glenn as the current draw is only about 600ma; That is not much but the truck set for about a month without being touched by anyone. These batteries have no dead, or weak cells that I could tell with both a temp compensated hydrometer, and internal cell resistance meter. All cells read very close and linear to each other. I did pull the starter assembly and removed the solenoid. It's internal resistance is the same removed from the starter motor between the battery connection post and the starter motor post. The starter motor windings are near a dead short from the post to the case. I haven't taken the solenoid apart yet to flip the ring or replace the contacts, but will probably get to that tomorrow. Someplace around here I've got a few of those parts......

I've seen that trick with killing a running small engine. Never tried it myself. It's always been with a distributor type ignition, never a magneto.

Thanks,

Rob

I tried to keep up the batteries while you were gone but I seemed to be partial to the B instead of the others. Next time your gone give me the key to tha house and i'll take care of everything inside also.

mike

[Rob]

I tried to keep up the batteries while you were gone but I seemed to be partial to the B instead of the others. Next time your gone give me the key to tha house and i'll take care of everything inside also.

mike

I should have thought about giving you the key cause the dog was awful hungry when I got home. He always likes a light snack and considers it a "gift from above". You did a good job maintaining batteries on both the A, and the B models. They fired right off.

Rob

[Mike]

I should have thought about giving you the key cause the dog was awful hungry when I got home. He always likes a light snack and considers it a "gift from above". You did a good job maintaining batteries on both the A, and the B models. They fired right off.

Rob

Me and tha dog would have got along just fine........ I'm tha dog whisperer...... it's tha refrigerator that I would have a hard time with since it had no slab of human inside it. I would have had to revert to slab of lab instead......... lab is a little too sweet for me ....... human is better with a little tabasco.

mike

[other dog]

I had the same trouble with the mixer. It took about a month for the batteries to drain too low to start it, and it only started doing this after 2 guys stopped by to look at it and started it up while I was gone. My wife was there, and I don't think it was anything in particular that they did, but I don't know. I just went and bought 2 battery disconnect switches and put them on it, because it sets for long periods of time anyway.

[Rob]

Went over to my electrical rebuilder last evening and purchased a couple of contact points for inside the solenoid, and flipped the copper ring around. Reinstalled everything and now my current draw is a whole 40ma. I'm sure this is driving the meter movement in the dash.

The contact points were quite charred where the copper contact ring slams home upon turning the ignition switch to the start position.

This current draw is less that 10% of what it was before fixing it.

Thanks,

Rob

[HK Trucking]

An alternator will easily draw 40 milliamps when the truck is shut off.

I checked one about a month ago that was drawing 60 milliamps. Took the alt. off, had it tested by our local rebuilder, all checked good.

[Rob]

An alternator will easily draw 40 milliamps when the truck is shut off.

I checked one about a month ago that was drawing 60 milliamps. Took the alt. off, had it tested by our local rebuilder, all checked good.

Yes I've seen that before myself. I have already had this alternator rebuilt, (Leece-Neville) because I had not history on it and it was very slow to pull in the regulator. Went ahead and put new diodes and fused links in it at the same time cause they're not much money. This truck had a consistent draw with the alternator disconnected also.

Rob

[Freightrain]

Hmmm, I let my B go all winter hooked up and it's been fine all these years. Actually going on 6+yrs for the batteries/starter when I switched it to Neg ground and 12v start. Didn't put a disconnect switch on it either.

In fact, I know the batteries are starting to fail as it takes some time for them to get above 12v when the alt kicks in. I pulled two off(since the one battery box was getting kinda weak anyway) and now it still starts easily with just 2 batteries. Guess I must not have too much of a drain on the system?

[Rob]

Batteries are rated at both cranking amps, and reserve capacity. The particular batteries are 450 min reserve if I remember correctly. This means with a full charge in the cells, (1.25 specific gravity level) and a steady 1 ampere draw on the battery at 70 degrees ambient temperature, the battery will be officially "dead" in 450 minutes, (1.10 specific gravity level). These figures are from my generator maintenance manuals and do have some leeway as far as tolerance as they are derived through laboratory measurement.

Citing that the batteries are in parallel with each other the adds to the cranking amperage available, and the reserve capacity of the battery bank. Now with a steady electrical draw of 600 ma against this battery bank you would have approximately 2/3rds of an amp steadily depleting the charge. If you have 900 minutes of total reserve capacity available, you would with one ampere load be dead in 900 minutes. With 2/3 ampere draw, you could add another 1/3 of the time to the total meaning 300 minutes, or 1200 minutes until the batteries were officially dead.

As you know there is 1440 minutes in a day, 24X60=1440. Theoretically, a battery bank with a one ampere load impressed upon it with the above mention criteria would be "dead" and require recharge in less than 24 hours. I think it could be ascertained why batteries deplete with a small load upon them. As the available battery voltage drops in the storage cells, the current declines also as voltage/resistance equals current expressed as: E/R=I. The resistance in this circuit would remain constant with the voltage impressed upon it lessening as the battery bank discharges.

Rob