# Curtis 1204b & 1209b voltage limits



## rmay635703 (Oct 23, 2008)

I am wondering what the upper voltage limit of the Curtis 1204b is, in my case its a 36v/48v 275amp model. I have one unit tore apart that I plan on upgrading the mosfets and caps on, the issue I have is that the controller seems to shut down somewhere above 67 volts (not always at the same voltage, I have gotten it to run at 72ish a few times)

In any event I would like to slightly upgrade the 1204b to have an operating range of 48v-96v (something I have probably mentioned before) So I can run a hybrid pack of lithium & greensaver gel batteries in the zx40 minivan. Effectively get up to speed using 96v then use the series parallel contactors I have to switch back to 48v for the long haul
I have found the 1204b runs fine with 60v of lead and has for many miles but the control board is unhappy above 67ish volts. With the caps and mosfets replaced I should be able to run higher voltages but I either need to defeat the overvoltage shutdown (something I don't know how to do) or provide regulated power to the right bits in the control board, something else I don't know how to do.

If anyone has a simple suggestion of what specifically to do to the 1204 to bypass the the overvoltage shutdown I am all ears, with the caps and mosfets replaced there should be no issues on "that" side at least. A good photo of where to intercept would work. 

Anyway I own a set of contactors a 300amp diode and other goodies laying around that likely can be used to make the zx40 into a 48v/96v with a series parallel battery pack. AKA I can flip between 48v and 96v as needed and get away with a small lithium pack. I already have the dash and contactors in the car intercepted so I can run an independant 48v line to power them.

If I cannot find a reasonable solution I will use as is with a 60v set of lithium batteries and run a hybrid pack such that when the lithium are dead the gel batteries will take over and prevent them from being overdischarged. A simple diode seems to work fine for this since the lithium battery range (I have selected) overlapps the fully dead gel range by a large margin.

In the winter the greensaver gel batteries sag terrible (around 5 deg f) and the range/speed is reduced greatly, they are also a pain to charge in the winter cold, current charger does not appear to be up to the task. My hope was lithium could help ease winter travel issues a bit and provide a bit of a speed boost when needed without a massive weight gain.

Cheers
Ryan

PS I also have an ancient 1209b available to me and I am curious about its limits but from what I remember it is much less forgiving to overvolt than the indestructable and slow 1204. Since I am using it at 48v when it is a 72v controller I figure it would be best used at a higher voltage, seems like 84 volts was a hard limit.

Ah well


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## Electric Forklift Guy (Dec 13, 2012)

What is probably going on is the internal 14Volt internal power supply is being overwhelmed by the higher battery voltage and causing a "Hi Pot" error.

The 14volt regulator powers the logic circuits and if it gets over 18 volts you'll start getting false errors.

Curtis designed the power supply to handle up to 62 volts so a 48volt charger wouldn't blow it up if the key was left on during charge

So unless you have the ability to modify the internal power regulator , you're basically stuck with 48 volts.

If you can modify the 14volt regulator , double check the voltage rating on the filter capacitor before hooking power up.

P.S. the 14 volt internal power supply is the reason the low voltage cut out kicks in between 16 and 18 volts.

I hope this helps.


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