Car batteries are the only power sources that I've seen rated in cold-cranking amps. I know a little about electronics and am familiar with a standard amp, but how does that relate to cold-cranking amps?

The reason that I ask is that I've got my engine out and would like to do some testing with it out of the car that would require turning the engine over with the starter (i.e. compression, leak-down tests). I've got a 12 VDC, 40-amp power-supply (thing weighs like 25 lbs), and I was wondering if it has enough current to power a starter for a few seconds at a time. I know that I could always just use the battery, but I'd be nice to use something that doesn't need charging.

Thanks

 

I don't know exactly what a CCA is other than to say that more is better.

However, 40 amps is not near enough to turn over an engine, even with a gear reduction starter which typically draws fewer amps. When that thing hits the spur gear it'll spike several hundred amps @ 12V, but even under constant cranking it'll be over 100A.

 

O.K. - You started it...

An ampere is an ampere is an ampere.

Here are a few things I know that might be related to your question;

Most automotive batteries are rated in cold cranking amperes, or CCA. This is the maximum available discharge current that a battery can sustain while maintaining at least 8 volts (65% rating) with the battery at 32°F / 0°C.

Most any other battery or cell, whether automotive deep cycle, backup, industrial, or otherwise, is rated in its ampere/hour rate. This is the maximum rate at which a battery can discharge while maintaining rated voltage for at least one hour. Some automotive cranking (starting) batteries will still display the amp/hour capacity as a secondary rating, or "reserve capacity" rating.

For automotive starting purposes, the CCA rating is more appropriate and relevant. A battery with a high CCA rating may not have a lot of reserve capacity, while a higher amp/hour rated battery may not be able to develop the same level of peak output current necessary to operate a starter as a starting battery. Starting batteries are designed to produce a high current for a short interval, then recover quickly. This kind of duty is not suitable for a deep cycle and "kill" one in a hurry.

As for the starter/charger you have, it likely doesn't have very good rectification, so it isn't producing very pure DC voltage output. It's probably more of a pulsed DC, and the battery that it is charging acts as the capacitor to filter and smooth the DC pulses. Without a battery connected, any load connected to it may not operate as expected or intended.

Concerning starters, a typical single stage starting motor (not a gear reduction unit) will have a free-running current draw of 85-100 amperes at rated voltage. I doubt that your charger would sustain that for very long.

You might want to consider using the charger in conjuction with a battery to make sure the reserve capacity is there and the DC voltage is more direct and "clean".

 

Quoted from this site (lots of battery info for reference):

http://www.stealth316.com/2-dynabatt.htm

"Cranking amps is a general standard for rating the output and capacity of a fully-charged battery. There are three specific standards.
CCA - (cold cranking amps) the number of amps a battery can deliver for 30 seconds at 0ºF (-17.8ºC) and not drop below 7.2 volts.
CA - (cranking amps or sometimes marine cranking amps, MCA) same as CCA except the temperature is 32ºF (0ºC).
HCA - (hot cranking amps) same as CCA except the temperature is 80ºF (26.7ºC)."