bench testing distributor with some experimenting

[Barlow L]

Been away for a while folks. My Dad passed away after a hard fight with cancer. Been hard to get into the shop for fun stuff but I'm getting there.
Anyhow, Had a Distributor for a customer on the bench for months(loaned him my good one to keep driving). Finally got it rebuilt and wanted to bench test it. Normally I would drag two 12 volt batteries, jumper cables and test leads to the bench BUT, since I am getting set up to anodize aluminum I had bought a nice 0-30 volt 0-10 amp power supply.

So, I took a solid piece of copper wire screwed to the housing and bent it over to the coil secondary with about a half inch gap. Turned on the power supply, tuned to 24 volts and spin the shaft. Nice strong blueish white spark. Current was bouncing from 0-2.300 amps as rotating.

I then turned voltage down to 18 volts and spun the shaft, still nice strong blueish white spark, I did not pay attention to Current at this setting.

I further turned voltage down to 12 volts and spun shaft, still nice strong blueish white spark. Current was 0-1.200 amps as rotating.

There are my findings, I am not smart enough to know long term effects on the electronics or coil if running lower voltage. HOWEVER, I would think with the lower voltage and current, the coils would not overheat?

Older civilian vehicles used an external resistor to reduce run voltage to the coil being a ballast resistor or resistor wire.

Ok so time for you smart folks to shine and tell me why reducing voltage to the coil/electronics is bad or not beneficial to making the coils last longer.

Lee

[m3a1]

I'm going to take a stab at this and say Ohm's Law would be applicable to the situation you are describing. Still, electrical stuff is NOT my forte'. Hoping some of the other, more learned fellas will explain it. It HAS been discussed that coils do have an input 'range'..thus a 12v coil (or 24v coil for that matter) doesn't necessarily have to have 12v (or 24v) to do it's job. Both can get along nicely with less but there are limits and I think that is because of Ohm's Law.

[raymond]

Not sure about DC, but with AC, low voltage is just as, if not more harmful to electronics than high voltage. At the company, we often did our own repairs to circuit boards on cash registers, printers, disply screens, etc. Hogh voltage can be protected from with a surge suppressor or a thermistor. In fact, most AC devices "destroyed" by a voltage surge can be repaired by opening them up and removing the thermistor from the power supply and soldering in a new one. A small fuse is often also just in front of the thermistor.

No such protection exists for low voltage outside of a battery backed uninterruptible power supply.

Again, this is all electronics, not coils.

[rickf]

Electric power is electric power and ohms law reigns supreme. AC-DC does not matter, music groups notwithstanding. Don't like that group anyway. Your readings are consistent with a Chinese coil so I would assume that is what you are using. Here is the kicker, As the voltage comes down so do the amps which means the coil will run cooler but there is no free lunch here.

Here are the figures according to Ohm's law and figuring 11 ohms resistance for a Chinese coil.
12 volts will give you 1.09 amps out at 12 volts in.
24 volts in will give you 2.18 amps out.
I can't tell you the secondary voltage since that is a product of the number of windings.

On an American coil with 6 ohms resistance and 12 volts in you will get 2 amps out.
With 26 volts in you will get 4 amps out.

Needless to say this coil is going to run hotter in theory but if you feel the difference in weight between the two it is substantial. The American coil uses heavier windings and probably more of them.

Another thing to keep in mind is that the voltage is what gives you the spark but the amperage is what put heat in the spark. A static electricity spark can have a hundred thousand volts and simply sting you because the amperage is in the milliamp range where something with 1-2 amps and only 12 volts can kill you under the right circumstances. If it goes through your heart you could die. I long ago made it a habit that when I am working on or near plug wires to always have my arms touching the fenders. That way if I got zapped it went right to ground at the elbows.

The reason I point that all out is that even though you are seeing a nice blue spark it is not as hot as the 24 volt spark. With that said I personally know of three people that have run and are running 24 volt coils on 12 volts with no problems.

Here is a thread done by a member here with a lot of expensive test equipment. Check it out, there is some interesting stuff in there.

viewtopic.php?f=2&t=12808&start=15

[raymond]

All in all, my experience is that low voltage is more harmful to electronic components than high voltage.

Not sure about coils. To me, it seems a coil, with all it's windings, is essentially a transformer.