calculating needed gauge of long cable from power supply to charger?

He is worrying about nothing.

Any 8 to 10 gauge (AWG) cable would do fine.

...... Phil

First note: I heartily recommend referencing Anixter's handbook of electricity as a source for your questions on wire gauge and ampacity.

Your calculations should factor an 80' loop length (you will be pushing and pulling current both into and out of the charger, so double the linear distance to get loop length). The sites you quote seem to be taking that into account.

Voltage drop of #10 is roughly 1 ohm per 1000 feet (more conservative references are as high as 1.25 ohms per 1000 at 75C), so expect 0.08 ohm in your power transmission cable. At 10A full load, you will have a voltage drop of 0.8V, and a power loss of 8W. If you want to be very conservative figure 10W, and that 10W will be spread out along the length of the cable. It will remain cool to the touch. Decide if that is acceptable efficiency. #10 should be your minimum choice.

This link doesn't work, I presume the elipses are fouling it up.

This link is recommending AWG #4 to carry 12V at 20A 40'. That's a good number based on the application. This source wants to squeeze voltage drop to a minimum. The calculation is using 12V solar panels to charge a battery.

This is the site that is giving you AWG #12 to push 20A along 40' one-way (80' loop length as mentioned before). I figure they're calculating for a home circuit, where the wire is being sized for a 20A breaker. That's a different application as well, but ISTR that electricians will upgrade house wiring to #10 for a 20A (as opposed to 15A) breaker. I could be wrong on that.

If you want to be conservative in both design and cost, use AWG #8. #2 is going to be expensive and bulky, and #8 will have about half the power loss of #10. As the absolute most conservative design, use #6. You can find #8 in quality cable (THHN rating) for probably 40c per foot, so 100' will cost you 40 bucks, a lot less than shelling out $84 for a pair of crappy jumper cables that have to be spliced together. See if you can find #8 or #10 two-conductor sheathed THHN cable. That might be your best bet.

What, laying on the carpet in the living room? Do you have a puppy? Small children? Ah, I dare say, a wife who likes a nice tidy living room? 12V isn't a lot, but at 10A it can produce a big flash and melt and burn things (like nylon carpet, or a puppy's tongue) when shorted. Run it through the attic. Er, by the way, does your Mastech supply have output short circuit protection?

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Thanks so much for the terrific answer. No, no puppy, children, wife. Mastech does have short protection.

The thinig that is so attractive about the jumper cables is how flexible they are. The multistrand wire at home depot has very thin insulation and is not flexible at all. You have to bend it. Is that two-conductor sheathed THHN cable you mention flexible like a jumper cable?

Jim

Ok, so you have no pressing need for output circuit protection.

Tray, duct and simple building wire aren't necessarily flexible. Welding cable is, but it's more expensive and tends to be thicker gauges.

Much of my answer is predicated on the belief that a wiring job should be undertaken with a degree of professionalism and craftsmanship. I wouldn't take the jumper cable approach, especially if splicing is required, but it's your project. I'd find a more suitible route than across the floor, unless it were a very temporary installation. Take the time to get a primer in cable crimping; as a minimum, you want good crimp connections at both ends of the cable. I'm hoping that you're not considering using the spring-jaws as your permanent connection, but again, it's your project.

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Well, first, I rent, so can't make any permanent installations. Plus the power supply may travel with me to the field and back and forth between my motor test stand in one room and building bench in the other.

I bought very heavy copper lugs for 8 guage wire, they screw down. I bought a split bolt splicer. I haven't done anything yet, still thinking things through. I'm noy sure how'd I'd insulate the splice.

But you raise an issue I have already been wondering about with your question of using the spring-jaws.

When we charge batteries at the field we use a charger connected to the car battery. That uses small spring jaws that come with most every charger. In this and other cases where a spring jaw is used, the total area of jaw touching battery must be very tiny, compared to the thickness of the cable.

Is this a problem? It seems like the jaws would heat at those points, and provide a tremendous resistance (though the distance is short, true).

Stick/arc welding cables;long flexible & EEK $$$

I wouldn't use a split-bolt for a temporary or mobile cable. Typically a split-bolt is used with bare ground cable, at least in my experience. When insulation is required, I've seen it wrapped with electrical tape. The splice is bulky, and the insulation wrap prone to fraying and peeling if moved around a lot.

I'd use an inline crimp connector, which may come with its own heat- shrink tube insulation. "Burndy" is a good source for info on these crimps. You realize you can't use your 8ga. lugs on the 4ga. wire, I'm sure :-)

It's a trade-off. Loss of conductance vs. ease of use. In the case of mobile application, the ease of connection to the battery is of primary concern.

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Thanks Charlie. It is possible to quantify how much conductance is in effect when using the clamps? I am trying to decide if this is a safe method, I need to deliver 10 amps/60 volts, would it drop that, or just be a bad idea?

Thanks...