Paul & Sabrina's cheap DIY 144v motor controller

[mora]

New power PCB design has tinned contacts for B+, B- and M- copper bus bars. Do I need to heat and tin my copper bars before attaching them to the PCB or would I be fine without soldering? I was going to use some conductive glue and simply clamp them together like I did on earlier design.

[MPaulHolmes]

You don't need to solder them to the power board. Just use the conductive epoxy again. At least that's what I've done and it seems to work fine.

[mora]

Thanks for the info. It took few weeks to get proper flat copper sourced so I can start my controller rebuild now. Hope to finish it soon.

[isaac_alaska]

A couple weeks? Onlinemetals.com has really good stock on copper, and they are reasonable prices. Plus they also offer cutting (for like a dollar per piece) and they have pre cut pieces (random length between 10 and 12 inches) that seem to always be around 11.5 inches. And they have 110 alloy, which is about the best alloy u can get aside from 111

[mora]

Yea, I took a look at their store before but didn't find any info about international shipping fees. Maybe I should have asked them. I got some copper bar from local scrapyard for my previous controller. It was cheap, hehe. I asked some companies if they had flat copper and best offer I got was 4m long bar. Oh, and most of companies I asked didn't sell to individuals. After all the searching I asked the same machinist who made my motor shaft coupler. He had some thick pieces of copper and cut them to bars per my needs. Aluminium is no problem to find.

[isaac_alaska]

oh! i had forgotten about international shipping. online metals only ships ups, but i believe ups has international shipping options. if you can find it locally though, that's perfect

[mora]

Success. Controller works fine after repair. I replaced all the mosfets, whole power board and two diodes. Now voltage goes to 144V during precharge and even voltage sag seems to have lowered.

Question: for how long should caps remain charged? My previous controller lost cap charge in few seconds after opening the main contactor. Rebuilt controller holds charge for minutes and voltage decreases very slowly. Could that quick voltage drop have hinted me of developing short?

[mrbigh]

I think you answered your own question.
You should install a discharge resistor between pre-charge cap. (+) and (-) 12Kohms x 10 Watts to avoid those sudden electrical discharges.

[MPaulHolmes]

I used my math 102 class today to do a series of voltage, current and rpm measurements on a DC motor. the results:

if voltage is fixed, the amp-rpm curve is linear. for different voltages, the amp-rpm curves are parallel. So, you just need 2 of 3 volts, amps, and rpm to know the other one.

[tazziboy7]

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