C1 Battery-Generator Help

[Darren H.]

New to me 58. Problem with the battey draining down in just a week. When the car is on if the generator is working properly should the charge on my battery be higher than the 12V with it off?? As it should receive some back charge right??? Or does it work differently than an alternator??

If it doesnt charge back where is my problem?? The generator or potentially elsewhere??

Any help for a novice would be appreciated! tHANKS`

[Dan D.]

Re: C1 Battery-Generator Help

Darren, With the motor off a fully charged battery should read a little over 12V. You need a good digital VOM to measure this. Then start the engine and the voltage should gradually rise as the battery begins to charge. Fully charged it should read a little over 14V. If the battery is not fully charged it will take the generator some time to get it up, but you should gradually see the voltage rise. The old DC generators do not charge like the newer alternators do. Alternators will bring a battery up with the engine at not much more than an idle. With a DC generator, you have to get engine RPMs up to increase the charge rate, and at best is only 30 amps. Another trick to try is monitor the battery voltage with the engine running and then turn on the headlights. The charging system should compensate for the increase in current draw and keep the voltage near where it was. Keep in mind the old DC generators were prone to failure. It is not uncommon for them to give up the fight. In a DC generator the charging current is developed in the armature and brought out by the SPLIT ring communtator and brushes. In an alternator the charging current is developed in the outer stator windings. All the rotor does is provide excitation current via the much smaller SLIP ring communtator and brushes. Another thing you can do is ground the generator field terminal with a screwdriver (make sure you are not on the aramture post). Grounding the field will make the generator put out full current, and is a simple test to determine if a charging problem is in the generator or the voltage regulator. Good Luck -Dan-

[Dan D.]

Re: C1 Battery-Generator Help

Darren, I should also add that you say the battery drains down in a week. It could be you just have a bad battery. Is it very old? It may be sulfied up if it sets a lot (there was a long post on this late last year). But checking out the charging system first will help tell you where the problem is. And there is only the battery, generator, regulator, and possibly the wiring. -Dan-

[Christopher R.]

Re: C1 Battery-Generator Help

Are you using a battery shut-off switch? Most people use the "green knob" kind. It's a good practice for all old cars. NCRS gives you some extra points in judging for this. Even without, you'd want to use it anyway.

1. If you don't have a shut-off switch, and your battery drains in 1 week, you either got a bad battery or a short in your electrical system.

2. If you are using a shut-off switch, and your battery drains in 1 week, you've got a bad battery.

How old is the battery? If it's more than 4 years old, replace it. Install a green knob in any event. And, store the car with the battery connected to a self-regulating charger. See the archives for discussion on brands. I've got a Battery Minder.

At idle, the generator is not charging. It doesn't start to charge until around 1000+ rpms.

[Edward J.]

Re: C1 Battery-Generator Help

Darren, a good number to remember is, 12.66 that the state of a full charged battery. anything below is this is in need of charging, if the battery does not reach that 12.6 volts when charged it may be time for replacement. keep in mind the some of small trickle chargers out there may not let the battery reach that state of charge.

[Jim T.]

Re: C1 Battery-Generator Help

Darren something else you can try. If your car sits for several days or longer and is not driven you can disconnect the positive battery cable at the battery or unbolt it from the frame. Do this directly after driving and measure the voltage with a digital volt meter. Check the voltage before connecting the negative battery cable. A battery will normally show a reduced reading if the initial reading was say, 13.1-13.3 volts, however it should be above 12 volts, my batterys maintain 12.6-12.7 disconnected.
The above is from my experience of disconnecting the negative battery cable in my 68 and 70 when I am not driving them every week. With the negative battery cable disconnected there is no parasitic drain.

[Jack H.]

Re: C1 Battery-Generator Help

Dan's advice is dead nuts on! Generators have a 'cut through' profile meaning their output runs in lock-step to their RPM. At the low end, below, say 2000 RPM, there's little, if any, appreciable net power generation to supply charge to the battery, so you have to REV the engine to see the battery voltage climb.

The same is true of alternators, but they have a MUCH smaller 'cut through' window and they're generally capable of delivering charging current to mask typical battery draw loads at/near engine idle RPM.

On discharge. Yes, a battery will 'leak' (internal discharge) when left to sit. The discharge rate typically runs something like 1-2% per day. So, if the battery was fully charged when the engine shut down, it ought to make it through a week of sitting idle.

Two things change when battery's naturally age: (1) their internal self discharge rate climbs, and (2) they drop the amount of change they can hold (plates corrode/oxidize). But, this can be quite easily checked at a competent auto electric shop.

They can load test your battery and that will tell you EXACTLY what it's CCA (cold cranking amperage) is. Each battery has a rating and you can literally watch the measured CCA drop with respect to its rating as the battery ages/deteriorates.

Last, the most common cause other than simple battery aging for not being able to hold a charge is parasitic load(s). Things like glove box lamps that don't switch OFF when the door is closed are often 'guilty' party sources of excess storage drain...

[Jack H.]

Re: C1 Battery-Generator Help

I forgot to mention another source of discharge common to generator equipped cars: the voltage regulator...

These typically have three solenoids inside. One is used to pace output voltage, the second regulates max current output. And, the third solenoid has the task of turning the generator's field winding current on/off. It's supposed to open circuit when the engine shuts down...

If that solenoid is 'sticky' and fails to release (open up), you'll be draining the battery with the engine shut down and the ignition switch turned off! Again, a competent auto electric shop can quickly determine if that's an issue with your car...

[Darren H.]

Re: C1 Battery-Generator Help

Brand new battery....drained it down again to dry...brought it back to recharge up to full power...they said battery is not defected. Drained down again....was planning on taking to someone this week, but thought I could figure something out this weekend...I drive the car every other day, so its not a sitting duck!

I was disconnecting the negative for the last week, but now I the hood release is only releasing one side and I cant get into the hood!! Any tips for this?? Looked for the cable from inside and just cant get the hood to release on one side...

thanks

[Jack H.]

Re: C1 Battery-Generator Help

You should be able to get to the battery cables from the bottom side of the engine compartment with hood latched... The positive cable goes to the power stud on the starter solenoid. That should be easy to reach from below.