# Curtis controller voltage questions [was Re: Re: Could higher pack voltage be steppe



## EVDL List (Jul 27, 2007)

>> Is there any way to step down that pack voltage to
>> around 150-160 volts for input into the existing
>> Curtis 1231 controller (rated 144v nominal max)? 
> 
> The Curtis 1231 is rated for a *nominal* 144v pack maximum. You really 
> don't want to run it with a nominal pack voltage above this. The parts 
> inside are rated at 200v peak. A 144v pack freshly off a 2.5v/cell 
> charge will be at 180v, and there will be voltage spikes that go above 
> this.
> 

Hi Lee and other curtis specialists,

I have a 1221R rated at 84V, 375A. I see peak battery currents of up to 
500A and quickly settling to 350A then down to 250A when I push it. I 
try to drive with less than 160A which is 1C for my batteries.
I currently run my curtis with 90V nominal and am wondering if I can 
take it any higher, i.e. if all curtis rely on the same parts hence I 
could do a 120V or 144V pack without having to replace parts?? or is 
there a fair chance that something will break?

I suspect I have to open it and adjust some pots, like over voltage? and 
regen voltage? .. I notice that when my batteries are pretty full and I 
use regen then it can be very choppy, especially at slow speeds. With 
empty batteries this problem is not present. Hence I believe that my 
increase from 84 to 90V nominal already put the regen setting to its 
limit. What other things would need adjusting and does anybody have a 
schematic or guide which pots are for what. I have looked at the one 
from Otmar which I would use as an initial guide if there are no other 
guides.

Based on the feedback I received on this list earlier I came up with the 
following plan:
If I can do a higher voltage pack with the curtis I would go for 84V out 
of my 6V 160A gel blocks plus an additional 36V out of three 12V 100Ah 
blocks. I would use the 84V for my cruising load and when I need more 
power I would switch in the additional 36V via two large contactors. 
This should get me more RPM in 2nd gear and hence more speed without 
increasing amperage. I would need to monitor the 12V batts closely, they 
would behave like weak blocks and be empty first but I would only use 
them for accelleration. When cruising or when in regen mode the 
controller would only be connected to the 84V from the main pack.

Alternatively I was thinking about keeping the current 90V pack of gels 
(which at moderate currents is still good for up to 35 miles) and 
have a second (small) 84V pack of AGMs or similar. The second pack could 
be connected via a diode in parallel with the first pack and would 
deliver current when the gel pack sacks more than the AGM pack, hence 
the AGM pack should shoulder most of the high current draws while the 
gel pack should ideally provide a "base current" of up to 1C (160A).

A full AGM pack is too much money for me and I decided that even when I 
have to buy a new pack I will go with 6V GEL as they will last the 
longest. The only drawback is the weight as I am primarily concerned 
with the hillclimbing. I guess there is no easy way around it and as a 
second battery pack will increase my weight I think it is best if I only 
carry enough "additional" batteries for the peak usage times, i.e. 
accelleration and up to 3 mi. hills.

Am I on a valid track or do you guys think this is totally nuts?

Markus


----------

