Speaking Of Harbor Freight...

Building a very high quality adjustable carbon pile load tester is expensive.

High quality means a precise linear load action of the carbon wafer stack.

The only thing the HF unit is weak in is the smoothness of the applied load.


And the lack of a fan.

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ktmrfs wrote:

Cummins12V98 wrote:
Harbor Freight, NO THANKS!!!

in lots of cases I stay away from Harbor Freight. However in this case the harbor freight load tester is actually a good device and worth more than what they charge for it.

A lot of Harbor freight stuff is fine for the job, but if its a mission critical job, I buy quality. I once bought a Harbor Freight air conditioning manifold gauge set. I had it hooked up to the AC connectors correctly, and it blew up in my face. Lesson learned.

I have one I used it to test surplus batteries before buying
And I use it to test batters after installed
I used it to test the (5)*135ampHr = 675 ampHrs AGM bank I installed in the Safari
And the 200 ampHr 4d AGM, I put here in the Bounder

I've been very happy with it, good value
Your GC are not a problem

ktmrfs wrote:
in lots of cases I stay away from Harbor Freight. However in this case the harbor freight load tester is actually a good device and worth more than what they charge for it.

Occasionally I'll buy from HF. The 800A load tester Mex referenced is very nice but $500+ is hard to swallow.

Cummins12V98 wrote:
Harbor Freight, NO THANKS!!!

in lots of cases I stay away from Harbor Freight. However in this case the harbor freight load tester is actually a good device and worth more than what they charge for it.

Harbor Freight, NO THANKS!!!

CA Traveler wrote:
Mex Oops my bad as a post is missing.

1. I have the 2x GC2 220AH house batteries to test and appreciate your input. The tester manual says 160AH max for deep cycle batteries.

2. I also want to test group 31 950 CCA starting battery. Mfg says to use 1/2 of CCA as the amp setting for the tester and use the chart I posted. Hence 475A and check the voltage after 15 seconds. I'll try that but am doubtful that the el cheapo home type 500A carbon pile tester will really handle that amount of amps. .

My Harbor Freight carbon pile dual meter job hitx 450 amps with good batterie. Never gotten it up to 150.. I test my pair of 220 amp hour GC-2 at 450. THey pass till they don't then the new ones pass again.

Open your case and then saw and drill holes to fit a 120 mm 12 volt fan -- don't cheapen out here -- get one that blows some air.

"But there's no room inside!"

Who said anything about inside?

Get a wire screen fan guard.

Don't worry bout control or switches, when you snap the battery clamps off the fan stops. The fan will cool the unit down in a tenth the time.

Do the fan thing and you can test thirty batteries per hour if that's your wish.

Even a 1100 CCA 8-D isn't going to fall on it's ass when 500 amps is sucked out of it. A bit of common sense will reinforce the notion that at the 15 second mark the voltage isn't going down like disconnected elevator.

Bad batteries always dump volts rapidly when amperage draw is maintained. Very common is so see amps slump to 30 and volts at 4 volts and dropping.

Your 500 amp machine will work just fine. The manufacturer knows where he saved money and so he does not want to see it get very hot. Stick a fan on it and be done with it.

Garbage Reman Alternator ID
"Warranty Void If Battery Is Not Recharged Prior To Starting Engine"

Mex Oops my bad as a post is missing.

1. I have the 2x GC2 220AH house batteries to test and appreciate your input. The tester manual says 160AH max for deep cycle batteries.

2. I also want to test group 31 950 CCA starting battery. Mfg says to use 1/2 of CCA as the amp setting for the tester and use the chart I posted. Hence 475A and check the voltage after 15 seconds. I'll try that but am doubtful that the el cheapo home type 500A carbon pile tester will really handle that amount of amps.

So learning how to interpret the results and record them so that I have a baseline for the batteries to compare in the future for changes.

Others may have L16 or 8D batteries and need a 800A+ tester but I'd like to have a reasonable expectation of a good test with my batteries and the 500A tester.

Use a variable carbon pile load tester

In conjunction with a DC inductive ammeter

Place inductive loop around battery wire coming from the alternator.

Increase engine speed to 2,000 RPM

Slowly crank up the load. Observe inductive ammeter amperage it will climb.

At a certain point near 12 volts the inductive ammeter will start showing less and less amps as the carbon pile load keeps increasing

This is because the carbon pile load has reduced alternator voltage so low the rotor (field) current is insufficient to develop maximum excitation of the rotor field strength.