I'll be making a video on this soon, but aside from a few details, my giant load tester is done. At this point, it's fully operational. Because I'm trying to get the new packs in the car as soon as possible I took the path of least resistance and leveraged cheap and plentiful 3d printer parts - extrusions, corner fittings, even a printer lead screw. It easily holds 400 amps from a car battery for 15 seconds. The only part that seems to get a bit warmer than I would like is the top plate - but I used a piece of aluminum I had in a drawer. It was a perfect fit - literally no trimming, It was at about 120* F after the 15 second test. It's .125" thick. The carbon pile was around 100* F a few minutes later.
Can it really hold 7,000 amps? Well, compared to the Harbor Freight 500 amp carbon pile testers, with a few light mods (heavier cables, thicker top plate, bigger shunt/ammeter), yes. I initially bought 3 of those testers thinking I could hook them up in series. It would've worked, but two were defective right out of the box (1 was an easy fix, the other had a cracked disc in the carbon pile) and you'd need three arms to constantly balance the current and voltage between the 3. But those piles (that works on 2 levels - ha!) were 2.5" in diameter, about 1.5" thick with discs about .125" thick. Plus the design was stupid - the current traveled through the tightening screw; you could literally hear the sparking while turning the knob. The discs in my tester are 4" in diameter and .250" thick. The Harbor Freight units have about 7 cubic inches of carbon pile. My unit has over 100 cubic inches of carbon pile. And this thing moves like a dream - stainless leadscrew, brass nut; supported on ball bearings. In fact it has a built-in safety feature - let go of the knob, and the weight of the pile and the smoothness of the mechanism lets it float down fairly quickly. And it doesn't clank when it comes down; there's a fairly stout die spring on the bottom, sitting on a teflon "button" press-fit on the brass lead screw nut.
I apologize if this comes across as bragging; it's not really that as much as it is I'm surprised that it came together as quickly and the end result is as seemingly good as it is considering I had no plan in mind when I ordered those carbon discs a couple of weeks ago and a lot of it is leftover and recycled parts - the cables, the material for the top and bottom plates, heck, even the board was a part of a large equipment crate for studio equipment.
Anyway, I've rambled enough - here it is:
Can it really hold 7,000 amps? Well, compared to the Harbor Freight 500 amp carbon pile testers, with a few light mods (heavier cables, thicker top plate, bigger shunt/ammeter), yes. I initially bought 3 of those testers thinking I could hook them up in series. It would've worked, but two were defective right out of the box (1 was an easy fix, the other had a cracked disc in the carbon pile) and you'd need three arms to constantly balance the current and voltage between the 3. But those piles (that works on 2 levels - ha!) were 2.5" in diameter, about 1.5" thick with discs about .125" thick. Plus the design was stupid - the current traveled through the tightening screw; you could literally hear the sparking while turning the knob. The discs in my tester are 4" in diameter and .250" thick. The Harbor Freight units have about 7 cubic inches of carbon pile. My unit has over 100 cubic inches of carbon pile. And this thing moves like a dream - stainless leadscrew, brass nut; supported on ball bearings. In fact it has a built-in safety feature - let go of the knob, and the weight of the pile and the smoothness of the mechanism lets it float down fairly quickly. And it doesn't clank when it comes down; there's a fairly stout die spring on the bottom, sitting on a teflon "button" press-fit on the brass lead screw nut.
I apologize if this comes across as bragging; it's not really that as much as it is I'm surprised that it came together as quickly and the end result is as seemingly good as it is considering I had no plan in mind when I ordered those carbon discs a couple of weeks ago and a lot of it is leftover and recycled parts - the cables, the material for the top and bottom plates, heck, even the board was a part of a large equipment crate for studio equipment.
Anyway, I've rambled enough - here it is:
Last edited:
