The Stovebolt Site Forums The Shop Area The Electrical Bay Dead battery after a week of inactivity

I went to start the 51 with the 235 engine today. Dead Battery, not a peep . About a month ago I did the wiring for the "1 Wire" alternator and I've been having issues since then. Is that a Diode on rear of alternator? Is it possibly shorted? Any other ideas? Thanks, Jerry

A 1-wire setup draws a fraction of an amp of current pretty much continuously to keep the regulator alive. If you're going to let one sit idle for a few weeks at a time, either install a disconnect switch or remove a battery cable. A battery maintainer might be a good idea on one that doesn't get started every few days. Jerry

If your battery is any good the battery should handle a minute draw for a month easy. Disconnect the battery ground and install a test light between the battery terminal and the cable, if the light comes on bright you have a draw that will drain the battery. Make sure nothing is on such as dome lights. Then start eliminating (disconnecting) things until the light goes out. A very dim or pulsating light is common on such things as computers and radio memories but should not cause a good battery problems. Scott

Jerry, could you explain "keep the regulator alive". Thanks Don

It sounds like a parasitic draw to me, possibly coupled with a weak battery. My '38 has a one wire 6v alternator and sits for weeks at a time this time of year without draining the battery.

Jerry's advice is on the mark. A battery disconnect and a Battery Tender Plus are both sound investments.
John

I have done parasitic current draw tests on lots of vehicles, and it's not uncommon for the internal voltage regulator to draw a few milliamps of current on a continuous basis. A good condition battery with a full charge should sustain a tiny current draw like that for several weeks without losing enough charge to keep the engine from starting, so it's possible your new alternator is drawing too much current, or the battery might be on the verge of failing. A well-charged battery in good condition should be able to support a load test of 1/2 the cold cranking amp rating for 30 seconds, and maintain at least 9.6 volts with the load still applied. For instance- - - -a 500 CCA battery should test at 250 amps for 30 seconds, and the terminal voltage should be 9.6 Volts or more before the load is removed. A quick and dirty load test for folks without a formal tester- - - - -turn on high beam headlights, blower motor, etc., disable the ignition, and crank the starter for about 15-20 seconds. Battery voltage should not drop below about 10 volts at the end of the cranking session. One little tip- - - -the starter isn't bulletproof, so only run that kind of test once, then allow a cool-down period of several minutes. Jerry

I had the same thing happening to my street rod. I found that my alternator was drawing 1 amp with engine/key off. That is way more than it should. From my electronic background I knew I had a 'leaking' diode. My local repair shop couldn't replace the diode pack as the alternator is one of the new very small type that mounts very low on the engine (in front of the valve cover instead of above it). I did as Jerry suggest and installed a cut off switch on the ground side of the battery. The switch is out of a battery powered golf cart. Sliver plated high current contacts. I did run a #16 wire from the negative post into the engine compartment to bypass the switch so I can hook up my battery tender.

I think a battery disconnect is an excellent idea BUT my battery is under floor on passenger side, I have rubber floor mat held down by factory trim pieces . I am NOT ABOUT to pull the trim every time I shut down for a couple days. Has anyone put the disconnect on the starter where the heavy cable comes from the battery? What brand of disconnect did you use?
Thanks, Much appreciated.
Jerry

Is this constant drain only an issue with 1-wire alternators?

Dennis

Here's a disconnect that can be mounted under the hood with the proper size cables, and it has a removable key. This can also serve as an anti-theft device as well as preventing self-discharge of the battery.

http://www.summitracing.com/parts/pco-5575pt/overview/

Always use a disconnect with plenty of current capacity. The cheap 100-amp ones will not carry starter current effectively.
Jerry

Maybe take the wire off the alternator and tape it up, let the truck sit a few days, reconnect the wire and see if the battery is up enough to start the truck? Caveman test.

Tests like that are what separated cavemen from the apes?

Why not try it? Good idea.

Even a caveman can do it???

Yes, within our abilities.

Virtually all digital multimeters have a low-current ammeter built in. Disconnect the main charging lead from the alternator, and connect the ammeter in series with the circuit with the engine not running. (One lead to the wire, the other to the alternator output stud) It will be necessary to connect one of the meter leads to a different spot on the meter dedicated to "ammeter only". The current flow should be a very few milliamps. Anything approaching 200 MA or more is too much- - - -replace the alternator!

BTW, don't try to measure charging current with a digital meter- - - -most of them have a 10-amp maximum capacity and most alternators can go to 50 amps or more right after startup. You'll blow an internal fuse in the meter!
Jerry

Thanks, Jerry

When my friend with a 1-wire alternator visits, we'll check it out. Unfortunately, hibernation will put this off for a while.

On order, should be here Wednesday.

I had a bit of time today. I have not had time to do your "Draw down" tests nor test lite between Ground and Neg cable I did put cables on battery and started truck with that plug on rear of alternator DISCONNECTED and was amazed that the alternator STILL CHARGES according to the gauge on the dash. How is this possible as I thought an alternator needed a "Exciter" voltage from the battery in order to start charging. Was I experiencing a mirage?
Jerry

Do you have an ammeter or a voltmeter? Which alternator are you using- - - -the internal-regulated 10SI or the earlier model with a remote regulator? Neither one should function without the plug installed, although some of the 10SI models can get some feedback to the internal regulator through the diode trio and appear to be charging.

What was the voltage at the battery terminals? If the alternator is actually charging, it will be 13 volts or more.
Jerry

Hot Rod
The Alternator is a "Dixie 42 amp internally regulated 10SI" . In talking to the electric motor shop where purchased, It sounds like a defective alternator. He confirmed that while there is a small draw, that would not totally discharge a battery in a week to 10 days, He also confirmed that with the diode plug removed, it should NOT show charge unless the internal regulator is defective. As it is under warranty, bring it in and we will give you a different one.
I have an original ammeter in dash. I have not taken time to check the voltage at the battery while charging. Thanks again guys, I think this will be the solution to the problem.
Jerry

Update
That 42 amp"Dixie" int regulated 10SI alternator was exchanged and reinstalled a week ago Friday. That day, I drove the truck 18 miles to a welding shop for seatbelt installation. On Saturday, we completed that project and I drove the truck home and put it into shop.Fast forward to last thursday evening, I went to shop and just for chits and giggles, jumped into 1951 one ton and tried to start it. DEAD Battery. I called Electric Motor Co and explained . He said Bring IT back, I will change the Regulator inside that alternator because that company is USING a Self Exciting regulator in these 10SI alternator's. That Self exciting Regulator explains why that alternator was charging WITHOUT a 12 Volt Exciter voltage at the input side of diode. After MUCH head scratching by this Motor shop Owner, He said " Let me try this" He went into New parts room and brought out another alternator, This a 55 amp manufactured by another company. He put it on his test machine and said "This one operates properly as you requested, It does NOT charge WITHOUT the exciter voltage at the input of the diode and does NOT show "Draw Down" when it is not in service. This one costs about $20.00 more than the "Dixie" 10SI but take it home, Install it, You owe me Nothing! All he requested of me is to stop back and give him my feedback on whats happening when It is installed for a couple weeks. He said he would be calling "Dixie" to discuss this problem. , That He thought he knew Everything concerning Electric Motors, Generators and Alternators but this was a "Learning Experience" for him. This in my opinion is "Customer Service" beyond the call as this alternator had been purchased over a year ago. If anyone would like info on the Name , Address and Phone number of this company, please ask and I will share and send your business his way in an attempt to repay him for the way he went out of his way for me. Thank you guys again as we fight our way thru this.
Jerry

Thanks for the update! Even the 10SI alternators with constant battery voltage to one of the terminals of the rectangular plug draw a tiny amount of parasitic drain, but it is so small that it takes several weeks of inactivity to show a noticeable loss of battery charge. My electrical engineer brother was astonished that GM built their original wiring harness that way, but they were counting on the vehicle being used regularly enough for the parasitic drain not to become an issue. It sounds like the 1-wire setup has a great deal more drain than the way the 10 SI was designed to operate with.
Jerry