Deep cycle batterys, solar, amp-hours. question.
 

So I've located two L16 deep cycle batteries that, when new, claimed 340ish amp-hours @ full charge. They were taken out of commission but were part a large home array that didn't age the same. They are in good shape. I left the cooked ones alone. An electrician and I tried hooking an amp clamp to the positive pole of the battery with the car on, engine running, and everything (defroster, fan, radio, flashers, hlights, brakelights, everything) on. At the highest draw, the amp clamp was reading 3.7 amps. It may have been funny since it was possibly an exclusively AC amp clamp. Does anyone have reading from their vehicles that can back this reading up or for sure say that it's in error? I have a '97 civic hatchback dx.

My hope is to take the alternator belt out off of the engine, put the big batteries (320 lbs for the two of 'em) in the back, and run the car off of them, charging them with solar, and get some significant MPG gains.

I'll probably include a plug to hook up to since I live in new england and the sun can make itself scarce.

Any other pointers, comments, etc?

Amp clamps only work on AC. That's one scary electrician.

To his credit, he was skeptical that the reading would mean anything. Is there a way to comput the reading from an AC amp clamp to a meaningful value for DC? It did reflect increases and decreases when turning thing like lights, defrosters, ect on and off.

320lbs is a lot of weight, which will offset the gains of not having the alternator on. I'm not sure how much it will offset it by, but the weight will probably be noticeable.

How long is your commute, can you get away with only using one of the batteries?

And yes, that is definitely not right, 3.7A is like 45W, which is about what one headlight draws, let alone the entire car.

The batteries are 6 volts each, so I need 2 to get to 12 volts so the car can use the power. The electrician said that there's no way of halving the amp-hours and doubling the voltage or something like that, and that I'd need both batteries to get useful power.

No, the meter was reading the variations in draw, not the flow itself. Most cheap multimeters will have a separate setting for up to 10A, but be careful about overloading them. For small-draw items, you can take out the relevant fuse, and put the meter probes across the terminals instead. A cheap dash ammeter will give a rough reading for suspected heavy draws.

There's another thread around here that says that you need 14v to keep most of the car happy - as if the battery were on charge. The type of rig that boosts 12 to 14 can also do 6 to 14. The indiglo light in my wristwatch runs on 100V!

Hall effect sensors also work on DC. Inductive sensors only work on AC. It must be a cheap probe since all the good ones use Hall effect for higher accuracy on non-sinusoidal waveforms.

Could, then, the error have come from not disconnecting the alternator while doing this test?

I would think twice about adding 320 pounds of battery (plus mounting hardware strong enough to keep those batteries from getting loose in a accident!!) in a 2400 pound civic. That is at least a 13% weight penalty and it's not like your mother-in-law in the back seat occasionally, it's all the time! No alternator delete is going to make up for that.