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A Question on Delco Light 850 Operation...

I've asked about this before, but never really got a concrete answer. My Delco Light 850 is completely overhauled, mechanically and electrically. I wound my own replacement inner coil for the starting switch and it seems to perform normally. It does NOT have the fancy starting switch with the meter and manual settings, so the operator can physically set the run times...you just lift the starting tab, hold it until rpm's are up, release and away she goes.The manual I obtained only gives basic information about starting and running, but nothing about how the plant actually operates and shuts down.

My battery bank consists of four new 8 volt golf cart cells, and the coil is a modern 12 volt replacement with power through the original resistance unit and a toggle switch I installed to make sure the ignition is shut off. The points are in good shape with a modern capacitor across them. The mixer and fuel system is pulling fuel like it should.

Here's what's bugging me. I started it and it ran beautifully, with the meter showing a charge rate of about 10 amps. If I turn on my two 100 watt bulbs the charging rate increases properly. So far, so good. However, after running about 10-15 minutes it quits. Not having any other information, I created my own theory that the starting switch is basically a reverse current relay (a cutout) and senses that the batteries are charged, so it opens, killing the ignition. In order to prove this, I deliberately left my bulbs on for several hours, discharging the batteries. I then started it and it charged normally, but quit again after the same amount of time. I had to recharge the batteries with a 32 volt electric charger.

When it shut down the second time I was standing right next to it and I'm almost positive the engine quit and THEN the starting tab dropped....but I'm not absolutely sure and haven't repeated the test yet. So, it could be that some electrical fault is stopping ignition and dropping the tab, but again I'm not totally sure.

So, my question is, is the plant supposed to shut down by itself once the batteries are charged? Or is it possible that I have a bad (new) coil or other fault? I've tested the coil with a volt/ohm meter and the resistances are normal.

The reason for my quandary is that I can't see a fancy starting switch setup if the plant needs to be shut down manually. In other words, I need to know how Delco INTENDED the plant to stop! :)


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Re: A question on Delco Light 850 operation...

Until the Delco experts get here, have you tried immediately restarting when it stops? If so did it start? If not did you check for spark? May be that your new coil is breaking down when it gets warm.
Re: A question on Delco Light 850 operation...

Thanks Vanman......no, I didn't think of restarting it immediately which would have been the obvious thing to do. Ignition coils are funny critters and have been known to go open when heated. This coil is not near any heat source though, so if it IS bad it might just be a vibration issue....if indeed that is the cause. The resistance coil might be going open also as it heats up. I'll have to check both during another run. Also go over all my ignition wiring, switch, etc. Until then.....

I want to wait to hear from someone who has run (and stopped) an 850 on a regular basis. If the plant requires that you shut it down manually then I do indeed have a fault somewhere.

Will Barnhart

Last Subscription Date
Re: A question on Delco Light 850 operation...

The 850's had a flat (spring like) strip that went from the spark coil to the spark plug. It has an insulated top that one pulls of of the plug to stop the engine.

I have an original one on my 850.
Re: A question on Delco Light 850 operation...

Agreed......but my original coil was shot, so I replaced it with a modern coil and standard spark plug wire. Pretty sure that part of it is good........

Dale Burkman

Re: A question on Delco Light 850 operation...

The 850 is designed to shut down when the battery is fully charged. If you hold the start switch up it should run. The switch will drop when you release it. {If it runs holding the start switch up the ignition system is good.} Does this plant have the watt meter?

collector b

Re: A question on Delco Light 850 operation...

The watt and hours meter is designed to set the charging time
Just set dial the hours you like to charge the battery's
The dial runs back to zero and open a set of small points
Then it break ignition ,no spark
Check points for proper closing
My 850 points were not closing properly,when got hot and stopped the engine
The 850 don't stop by itself when battery's are full
Only stopped after the amount of hours you set the timing dial
Again, my 850 does NOT have the watt meter, where you can set charging times. Just a plain ammeter.

The starting switch stays up once the engine is up to running speed, so no major problem there. The hint about the points getting warm is a possibility, and one I'll look into. How did you finally isolate the problem?
Hi Dale, and thanks for jumping in..

This all happened some time ago and if memory serves, I lifted the starting tab and the engine did indeed fire up again......as soon as it pulled enough fuel from the tank to replace what ran back down. So, I think my ignition is okay.

I'm kind of busy now with family doings, but I plan on running some tests this coming weekend. I'll report back with good, solid information at that time. I'll test by running the unit and monitoring it until it shuts down. I'll then try to immediately restart it. The batteries are fully charged at this point, so I'll turn on a couple of 100 watt bulbs for a load.

Another possibility is the inner coil I wound to replace the damaged original. I wound it to 340 ohms if I recall and the original is supposed to be 300. Not sure if the extra resistance would play havoc with the circuit or not, but it's something to keep in mind.


850 delco light plant. where could i get the yellow markings restored on my start panel backing.:shrug: original little squares and numbers Jon

Steve Wright

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That starting switch is held up magnetically because the charging current is going through it. When the batteries get charged up the current diminishes and the magnet no longer holds the tab up. I use 3 twelve volt batteries anymore and this theory doesn't work that well cause the batteries continue to take a charge past 32 volts.

On the problem with it stopping, I have found that as the engine warms up the air (carburetor) needs to be adjusted a little. It slows a little and the amps drop enough the start tab drops out. On my 600 it kept doing that and I had to reach back and choke it a little. Couldn't make it through a parade without tending to it all the time. Found out if I filled the gas tank up it got along fine. Of course on the 600 it has to suck it up clear from the tank below. The 850 don't have that far to suck.

All of mine run with the original coil with the resistor on the end. By the book the coil is only running on about 4 volts because of the resistor. A 6 volt coil would be closer to the 4 volts if you didn't have an original.

Have fun :O

Elden DuRand

In Memory Of
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While I'm not an expert on Delcos (I've restored only one), I think the start coil is designed so when the charging current drops to a certain value, the relay drops out, stopping the plant.

There are two coils on that relay. One is of heavy wire and is in series with the load (batteries). The other one is of finer wire that is connected across the generator output (in shunt) and is wound in the opposite direction of the heavy coil, which would make it oppose or reduce the field of the heavy coil. When the voltage rises, the shunt coil magnetism reduces the magnetism of the relay until, at the desired generator/battery voltage, it is reduced enough for the relay to drop out and stop the engine. If the coil is wound with a different diameter wire or number of turns than normal, the drop-out voltage will be different.

For 16 cells (32 volts nominal), the full charged volts should not exceed around 37 volts when charging and that's the voltage where the relay should drop-out.

Maybe it would be a good exercise to put a meter across the battery bank and see what voltage the batteries reach when the plant stops. You can ether rewind the coil with the correct gauge wire, direction and number of turns or add resistance in series with it to get the voltage right.

Then, of course, I could be totally wrong. That's what you get for free advice.:eek: