# Curtis 1221C-7401 Over Voltage Derating



## Ziggythewiz (May 16, 2010)

This is meant to share, not encourage (nor discourage).

*Don't try this at home! (unless you can afford to lose a controller, YRMV, DSAYOR, etc.)*

*First the results, then some back story:* My 120V DC controller (Curtis 1221C-7401) is no longer happy running at 140V. It started cutting out and stuttering, bucking, etc sometimes cruising great.

Felt like I imagine overheating would, though no reason it should be, but last night it was even worse and when I pulled over I checked the controller and it was still cool.

I next thought it might be a bad pot (PB-5) but it checked out fine so I cleaned the terminals, replaced the connectors, and hoped for the best.

This morning I tried to do a test drive to see if it wanted to run, but only got the Curtis whine and 5 or 10 mph. No intermittent anything, just virtually no power, so I decided it didn't like the voltage. Pulled one 8V batt out of the circuit and it worked great, and no problems on the way to work. So apparently now 132V good (120V nominal), 140V BAD. I can only conclude something in the controller has degraded to the point where it wants to cutoff around 134-136V, where before it hasn't complained up to 145V. Luckily I had a soft failure instead of the smoky destructive one I expected.


*So the back story:* I started out with a 120V pack of marine floodies at 600 lbs. When they started to poop out on me I added an extra battery to for 10% more range (overvolting the controller by 12V nominal at rest, but they were typically sagging well below rating anyway). When that wasn't enough I started replacing failed batteries, and started upgrading from DC29s to GC8s. With the added weight of the GC8s I continued overvolting by 4 or 8 volts to compensate a little. In total I've ran the controller for ~18 months overvolted of the 26 months I've had it in operation. My 120V QuickCharger has been able to fully charge the pack to 140V, but at a greatly reduced rate.


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## miko81 (Apr 2, 2012)

to bad to hear.

it looks like this isnt good week for Curtis.

hope you will fix it


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## Ziggythewiz (May 16, 2010)

Nothing to fix. It works just fine at rated voltage.

Only time will tell if I've damaged anything (eventual smoking or further derating at rated voltage) that will reduce service life.


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## tenthousandclowns (Jun 21, 2012)

is 132 volts still the assumed maximum for the 1221c?


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## Ziggythewiz (May 16, 2010)

It's 120V nominal so peak would be 132ish...depending on the exact battery.


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