VCCA Home Forums TECHNICAL - GENERAL Electrical - 6 volt 6 Volt battery cable gauge

It also can be common for the original old large cables to look OK but the inner strands of wire are rotted away....this can be true with both the positive and ground.

There is a lot of good information in this thread. It makes good sense that a larger cable will be able to deliver more current than a smaller one, but they all terminate on a 1/4" lug on my starter.

With a brief internet search, I have found the following site:

http://www.interfacebus.com/Copper_Wire_AWG_SIze.html

This lists the current carring ablility of different wire sizes.

http://photovoltaics.sandia.gov/docs/interconnect.html

This site gives some information on voltage drop.

However, To do the calculation properly, you need to know what the current draw of the device is, in this case the starter. Then we could size a wire to have a voltage drop of 5% or less for a starter circuit using different lengths of wire. A 5% voltage drop on 6 volts would be 5.7 volts. I am no expert on voltage regulators, but it would also seem that you could set the regulator to charge at a little higher voltage to overcome voltage drop to the starter.

Can anyone tell me what the current draw is of a typical 6 volt starter?

One other question. On my car, the starter switch was replaced at sometime in the past with a solonoid switch. This connects to the copper lug on the starter by simply touching a slanting copper plate inside of the solonoid to the starter lug. This seems to me to be a very poor way to conduct current. Should there be a conductive grease applied to this connection?

I also found a calculator on the internet that I created the following table from. If I have done this correctly, these are the results. I took a stab at the current draw of the starter at 250 amps. It appears that a 1/3 reduction in power draw also results in about a 1/3 reduction in voltage drop.

current flow 250 amps at 6 volts

wire size voltage drop percent
per foot loss per ft.
4 0.062 1.03%
2 0.039 0.65%
1 0.031 0.52%
0 0.025 0.42%
00 0.020 0.33%
000 0.016 0.27%
0000 0.012 0.20%

(this table looks good in the edit mode, but somehow all the spaces were removed. I think you can still figure it out.)

If I have screwed this up, please let me know.

Thanks,

Rich

The information that I have gives-
Starter free running speed-5000 RPM with current draw of 65 Amps at 5.0 volts.
Lock load installed, current draw of 475 amps at 3.63 volts.
If the contacts are like a Chevrolet switch no lubrication is used and they have a self cleaning sliding action. The surface is cut at an angle where they make contact. The voltage regulator has nothing to do with the draw. The "amps" for the starter are stored in the battery and it can hold only so much - would be my description.
The cables I get at a farm store are 2-00 which is very large, very inexpensive and work very good.
The lug on the starter is 3/8" so the cable hole would be larger than that.
If you have been emailing me I can not find/open your messages for some reason.

Chev Nut is right, the regulator has nothing to do with the starter system as it only operates after the engine is started and running at enough speed to make the generator charge.
Tony

My comment about the regulator was concerning increasing the charging voltage to the battery. If the battery were at 6.25 volts then with the voltage drop to the starter under load, it would be closer to the desired 6 volts. In this regard, the voltage regulator settings would have a positive impact on starting current available.

If my table is correct, and I would like to hear from someone else on this to confirm it, the voltage drop on a 2 gage cable of about 2' in length is not all that great. Granted, the voltage drop on a 2/0 cable is 1/2 that of a 2 gage, but still not that great. That would also assume that my guess of 250 Amps for starting current is close to actual values.

Just a thought from a NON-Expert in auto electronics.

Rich

The paramount rule to remember here is that all of the cable that we are concerned with in these discussions will carry as much current as the starter will draw. The only difference is in how well it will dissipate the heat generated by the current flow. Hence, a #10 wire will overheat at 400 amps and burn up in a very short time and a #4/0 wire will carry that plus some all day long without overheating.

Here are some resistance specs of the cable typically used for our 6v starters in ohm/1000 feet @ 20°C;
1AWG = .134ohms,
2/0AWG = .084ohms,
4/0AWG = .053ohms.
By applying Ohms law one can see that very little voltage will be dropped across any of these cables allowing for virtually all of the voltage to be available at the starter. With a four-foot length it would be difficult to accurately measure this small of a resistance even with very sophisticated instruments.

Your 6v starter will probably draw roughly 400amp starting a 216 or 235 engine. If you take the resistance of a 1AWG cable i.e., .134ohms and divide it by 1000 you get .000134ohms, times a four foot cable, which happens to be the length of the one on my 1950, 3600 truck for example, you get .000536ohms. This times the 400amp current running thru the resistance gives you a voltage drop across the cable of .214v. Assuming your battery is fully charged .214v from the 6.3v will give you 6.09v available at the starter.
If you went to a 4/0 cable four feet long there would be a drop of .085v across the cable giving you 6.215v available at the starter.
With a difference of 125mv I doubt if you would notice any difference in the way the engine cranked.

You have to conceder the duty cycle of the cable. The duty cycle is based on a 5-minute period. The #1 cable will carry 250amp with a 100% duty cycle, at 450amp the duty cycle is reduced to 30%. By comparison a #4/0 cable it will carry 470amp at 100% duty cycle and 858amp with a 30% duty cycle.
So what this means is that if your starter can draw 400amps thru the 4/0 cable all day long and over a 5-minute period the ability of your #1 cable will decrease by 70%. Now of course you have to remember that the field coils in the starter are only equivalent to an 8 or 10 gage wire and because of that Delco-Remy service bulletins caution you not to crank the starter for more than 30 seconds at a time or you will over heat the coils and quite possibly burn the starter up. So keeping in mind that any electrical circuit is only going to carry as much current as its weakest link, I have to ask, is that 4/0 cable really necessary to feed the field coils?
Denny Graham
Sandwich, IL

Denny,

My research showed that voltage drop was not really an issue. Your response more correctly takes into account the current carring ablity of the wire. As you note, there is another limiting factor in the starter that is an issue too.

Maybe we are beating this issue to death. What size wire was originally used in these cars, and, is there any reason to believe that it is not still appropriate to use this size now?

Rich

The original cable that was on my 1950 is not as "fat" as the 2-00 cable I replaced it with. The original was still working fine. You guys are making a mountain out of a mole hill. Just use the proper sized cables, have a charged healthy battery with good clean connections, a starter the is in good shape and you will have no problems.

Amen, Gene, Amen!!!!