Cranking Amps uncoded

[M1008driver]

Every time someone asks about converting to 12 volt I hear how great the 24 volt system is for starting and how the 12 volt will not start in the winter.

I risk going out on a limb to say not necessarily...

When two batteries are connected in parallel they double the cranking amps, thus with a quality starter should have no trouble starting in the coldest of winters.

For example:

An Optima D31A has 900 CCA (Cold Cranking Amps 0 degress F). In parallel that is 1800 CCA.

The same battery has 1125 CA (Cranking Amps 32 degress F). In parallel that is 2250 CA.

As you can see in theory you should not have any problem with batteries in parallel during the winter. You will be cranking with the power of two batteries, not one as in series. I know the die hard purists will not want to hear this, but these are the facts that have been left out every time someone asks about converting to 12 volt.

Cranking Power

• Most vehicles are fitted with a single lead-acid battery. The battery powers the starter motor that cranks the engine. In cold weather, a battery may not deliver sufficient amps to power the motor. A second battery, hooked up in parallel, doubles the amps available.
  
  

Read more: Hooking Up Two Batteries in Your Vehicle | eHow.com http://www.ehow.com/facts_7718829_hooking-up-two-batteries-nvehicle.html#ixzz21UsvcKsU
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[uscgmatt]

You have double the amperage available but still only 12 volts. Think of the volts as water pressure the amps as water and pipe as the wire. You have more water available but still the same pressure, and pipe. the more voltage or bigger pipe, the quicker the water flows. Now if you double the wire size on the converted truck you can almost make it even to the 24 volt system.
My M35 cranks faster than my 6.0 Powerstroke which has bigger batteries but is 12 volt.

 

[phil2968]

Volts X amps = watts.
12V X !800 amps = 21600 watts.
24V X 900 amps = 21600 watts.
More voltage requires less amps. Ohms law.

 

[Ken_86gt]

Well, you said some of it yourself- with a quality starter....This has been covered in the past. In a perfect mechanical system with no losses it should not make any difference because the amount of work done is the same. But the starters are not the same. You can only get so much power out of it before you have to increase the physical size or voltage of the starter- which one do you think will cost less? You also need to consider the wires. If you cut the voltage in half then the amps double- did you double the wire size to account for the increased current flow? Can you have a reliable 12V starter based system- of course you can. But you will have to do some engineering to the original design. The 24V design works just fine. If you feel the need to alter it then have at it. Did you ever wonder why larger machines use 24v or even greater voltages for starters?.....I did some training on EMD based generators that used 120V DC starters- the batteries were in series. The engine was basically a train engine. There probably is not wire big enough to turn over that EMD at 12v...

 

[Keith_J]

At 0F, you also have considerable pre-glow. This causes voltage depression in already thermally reduced battery power.

Use the Edison vs Tesla debate here, you have a set resistance in the wiring causing voltage depression in the circuit. Edison lost out because back then, direct current couldn't be transformed, unlike the AC of Tesla. Tesla's AC system allowed for higher voltage transmission, resulting in less resistive loss AND the ability for a single generation station to service thousands of square miles.

Also, consider the 28MT geared starter for later CUCV applications. Being geared, it is far more efficient because it uses the 24 volt system to advantage, turning more of the electrical power into mechanical.

Back in the 1950s, cars had 6 volt systems. These gave out to 12 volt as they are more efficient in using copper wire. The Ford Powerstroke has a DC-DC converter which increases the voltage to fire the hydraulic boosted unit injectors for the exact same reason, 48 volts IIRC.

The problem with higher voltage DC (above about 30 volts) is arcing with conventional switches. Solid state high current devices like metal oxide semiconductor field effect transistors (MOSFET) can handle 100s of volts and amperes without arcing, these are the future for automotive switching.

 

[M1008driver]

Well, I will be honest here.

I did the Roscommon conversion last Saturday. I understand preserving these vehicles, I do. I use my truck in many desolate places and I need to be able to buy parts locally.

I used the Duralast Gold Starter with a lifetime warranty and new copper battery cables custom made to the right length. The old alternator is being rebuilt for a spare using CUCV Electric parts. I was even able to buy new belts for a K30 pickup and they fit just fine.

I have to admit chopping up your truck's electrical system can be a scary thing to do. My brother helped as he is handy to have around. We followed the instructions carefully. When it was time to start the engine, she fired right up easier than ever before.

The only thing left to do is replace the voltmeter. I have one on order.

I realize some of you will spit on the ground in disgust. I neatly saved the old system in case I ever change my mind. It is my truck and I am comfortable with the conversion. My trust went way up too.

 

[Keith_J]

Sell the 24 volt equipment to recoup your cost of change. I'm in the market for a working volt meter.

 

[forest522]

Very well put sir. I admire your honesty and candor.





QUOTE=M1008driver;1180151]Well, I will be honest here.

I did the Roscommon conversion last Saturday. I understand preserving these vehicles, I do. I use my truck in many desolate places and I need to be able to buy parts locally.

I used the Duralast Gold Starter with a lifetime warranty and new copper battery cables custom made to the right length. The old alternator is being rebuilt for a spare using CUCV Electric parts. I was even able to buy new belts for a K30 pickup and they fit just fine.

I have to admit chopping up your truck's electrical system can be a scary thing to do. My brother helped as he is handy to have around. We followed the instructions carefully. When it was time to start the engine, she fired right up easier than ever before.

The only thing left to do is replace the voltmeter. I have one on order.

I realize some of you will spit on the ground in disgust. I neatly saved the old system in case I ever change my mind. It is my truck and I am comfortable with the conversion. My trust went way up too. [/QUOTE]

 

[Skinny]

Do not forget the voltage drop scenario as the starter, solenoid, and wires heat up. This will create voltage drop and at 12v may be affected greater than at 24v.

The math comes out the same but in reality, it just doesn't function equally. If the starter cables remain the same size in diameter, the 24v system can supply more current with less voltage drop than the 12v system can.

 

[MarcusOReallyus]

Edison lost out because back then, direct current couldn't be transformed, unlike the AC of Tesla.

Oddly enough, due to those stubborn laws of physics that just refuse to change with the times, we still can't transform DC. We have to convert it to AC by some means (there are several) before we can transform it.