# EV loses 'power', draws more amps after 'warmup'



## frk2 (Jan 2, 2009)

I have a ADC 6.7" motor coupled to a Curtis 1209B with 72v deep cycle batteries.

At first I thought it was just in my head, but now my brother feels it as well. What happens is that if the car is sitting (not charging, just sitting) for a few hours and I take it out it'll perform amazingly for the first 10 minutes. Amp draw will be minimum (under 120amps) and I would get decent response from the car.

However after 5-10kms I would start noticing that the car is 'losing power'. It will no longer seem to have the 'punch' it did when drawing 120amps or even 160-180amps. This will slowly get worse to a certain point at which the effect would 'plateau' out. The only way to get the power back is to let the car 'sit' for 1-2 hours. Also the car slowly starts to draw more amps for similar acceleration and cruising. When 'cold' it would settle at cruising amps of 70-75 but after warmup it may rest at 105-110.

What could this possibly be? Are the battery wires heating up? The main wires do get warm but not hot. My motor temp stays under 45 celcius and the controller is not hot at ALL. Im guessing its a contact or the wire heating up somewhere causes a lot of restistance in the path and thus drawing amps. Any clues?

Thanks.


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## Gavin1977 (Sep 2, 2008)

What is your pack voltage doing during this "Event"


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## frk2 (Jan 2, 2009)

Its not voltage sag. Pack voltage sags to maybe 69V or 66V in extreme situations.


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## Gavin1977 (Sep 2, 2008)

OK then. Is it worth measuring the voltage at the controller while driving? This will then tell you if the problem is before or after the controller.

However if its definately not a bad battery and you are pulling an extra 30Amps @ 70v, something should be getting very hot. If motor and controller dont show an increase in temp, could it be something mechanical on the car itself? Dragging brake or something similar?


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## dtbaker (Jan 5, 2008)

sounds like aging or underwatered batteries to me. A loose connection would show same loss right at the beginning.

After charging, there is usually some 'surface charge' that holds your pack from sagging for a while, probably gone after 10 minutes. The under load you will start seeing more and more sag at less distance than you used to get...

How old are the batteries?
Have you checked individual battery voltage, or SGs to look for bad cells?
Have you checked/filled all cell water levels?

When you FIRST start out, under some load pulling 200amps take a look at the pack voltage, then after ten minutes or ten miles of driving around, then after 20 minutes or 20 miles. Are you seeing significantly more sag when under load?


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## frk2 (Jan 2, 2009)

Thats the problem - its not the batteries. Firstly they are pretty new and they are well watered and all cells hold good voltage. Even when pulling 200amps the voltage does NOT sag below 66v.

Even i thought it would be mechanical and got all my brakes serviced - new rotors/pads and checked each wheel individually for brake grabbing. A brake problem should also be obvious right at the beginning - why the 10 minute delay? beats me!


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## EV-propulsion.com (Jun 1, 2009)

I say you are out of battery power. In a 72 volt system, full charge would be @ 78.6 volts. 80% DOD would have your battery pack down to 71.1 volts (11.85 v for each 12v battery) remember, 63 volts (10.5 volts per 12v battery or 1/2 that for 6 volt batteries-you didn't say what you have)is *completely* dead-where your car probably wouldn't move.
I say you need bigger ah batteries-especially because of the low voltage system-or increase the voltage so the amp draw is less.......
Check your resting voltage after 10 minutes-if its anywhere near 71 volts, you're out of power.
mike
www.EV-propulsion.com


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## frk2 (Jan 2, 2009)

I think you mis-read me - 66v @ 200Amp draw!! at rest the voltage will climb right back to 74 or 75V no problem.


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## Stunt Driver (May 14, 2009)

Voltage sag HAS to increase after 10km of your ride. What is voltage sag on battery pack at, let's say 150A initially, and what it is after 10km?


It is much possible that you get additional 10% sag after 10km, which would be very noticable in accelaration. Besides, what is your range? My 72v system gives 15km on best warm day.


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## EV-propulsion.com (Jun 1, 2009)

your 74 volts is still @ 35% discharged, I think your situation is normal. With lead acid a definite difference in acceleration and top speed will be seen at a 25% discharge and get more pronounced quicker the lower it gets. After sitting 1-2 hours, the batteries will "get some charge back" and it will seem faster again (for a short time)
Mike
www.EV-propulsion.com


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## frk2 (Jan 2, 2009)

@EV-Propulsion: You break my heart! i was hoping to find some obvious problem and fix it  That does make sense though - specially the 'getting the charge back' since I know that happens with LAs. If only I could make my car work like 'that' all the time - guess I need to go to 96 volts for that to happen!  

Btw- regarding dead @71 volts. I have 6v batteries and the manufacturer INSISTS that at 80% dod the VPC should be 5.1V. This means pack voltage should be 61.2V - Does that make any sense? Usually ive seen 5.88VPC which would mean 70.56V


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## EV-propulsion.com (Jun 1, 2009)

Sorry to be the bearer of bad news... If you used lithium you probably would avoid the "slow down" as their voltage remains rather steady until the end. I think your voltage number is more correct-I don't see how it could be 5.1. Here is what I go by when using a voltmeter for a fuel gauge (for 12v batteries-yours would be half obviously)
100% charge= 12.65+ volts ea
75% = 12.45 
50% = 12.24 
25% = 12.06 
0% = 11.85 

these are slightly conservative numbers, based on 0% charge (11.85v) being really 80% discharged (which you dont really want to go beyond anyhow) 
where if your pack got to 11.8-11.85 you're really at 80% dod (just about where you said at 5.88 per 6 volt battery)
Mike
www.EV-propulsion.com


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## major (Apr 4, 2008)

frk2 said:


> I have a ADC 6.7" motor coupled to a Curtis 1209B with 72v deep cycle batteries...... When 'cold' it would settle at cruising amps of 70-75 but after warmup it may rest at 105-110.


Hi frk,

How big a car is this? Cruising at what speed? 75A is like 5 or 6 hp. Then up to 110A, about 8 hp. For the same speed?

Even though the controller isn't hot to the touch, it may be hot inside. And going into thermal cutback. From the spec sheet: 

Thermal protection and compensation circuit provides constant
current limit over operating range and under temperature and
over temperature cutback. No sudden loss of power under any​
thermal conditions.

Mechanical bind could be an issue. In the motor, tranny or interface, steel parts heat up, get bigger or longer and cause a bind. Notice any heat from there?​ 
Got any photos of your set up?​ 
Regards,​ 
major​


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## Coley (Jul 26, 2007)

On my 72 volt setup with 12 volt deep cycle batteries, if I hit 66 volts I am in need of a charge.

My charger puts them up to 78-80 volts (surface charge) after a 20 amp charge cycle, (2 hours)

After I draw them down to 66volts @ 80amps, then let up on them, they also show 70-72 volts, but they are just not going to go much farther.

I have a small hill to climb on the last leg of getting home. 66 volts puts me in 1st gear and crawling over the top. 0 degree day...

What does your car weigh and what type of batteries do you have?


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## Duxuk (Jul 11, 2009)

Coley, are you talking about 66V under load here which then recovers to up to 72V after you back off the throttle. I am just starting to test my nearly finished 72V trike and am going to use my volt meter as a fuel guage so I have been very intrested in this thread. Another question to FRK2 is what Ah are your batteries, and do you know your Wh/mile?


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## GerhardRP (Nov 17, 2009)

frk2 said:


> I have a ADC 6.7" motor coupled to a Curtis 1209B with 72v deep cycle batteries.
> 
> At first I thought it was just in my head, but now my brother feels it as well. What happens is that if the car is sitting (not charging, just sitting) for a few hours and I take it out it'll perform amazingly for the first 10 minutes. Amp draw will be minimum (under 120amps) and I would get decent response from the car.
> 
> ...


Sounds like a real puzzle.
Do you have a performance curve for this motor that you can share [spreadsheet or table is best]
Could you make a few measurements:
What are the current and motor voltage at full throttle launch from dead stop?...cold and hot.
What are the RPM, current, and voltage just at the point where current starts to drop in hard acceleration?...again cold and hot.
If you and your brother want to do a science project, record a series of measurements of the three numbers RPM, voltage and current [and temperature?]. Particularly when current is changing from increasing to decreasing and visa versa.
Gerhard


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## Coley (Jul 26, 2007)

Quote:
"Coley, are you talking about 66V under load here which then recovers to up to 72V after you back off the throttle."

Yes, sometimes it will only go back up to 70v but after setting for a while, they will show 72+.

The big cklue when you are pulling down to 66V is that the amp meter will read 80 or so. Then you are really getting low on juice.


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## frk2 (Jan 2, 2009)

major said:


> Hi frk,
> 
> How big a car is this? Cruising at what speed? 75A is like 5 or 6 hp. Then up to 110A, about 8 hp. For the same speed?
> 
> ...


The car is very small and lightweight. much smaller than a geo metro weighing around 650kgs (total with the batteries). 

Yes for roughly the same speed (50kmph). My brakes are the only things that get REAL hot (the wheels and the rotor can go upto 70-80 degrees celcius) but other than that nothing. This is a clutchless setup with the motor coupled to a mass reduced flywheel bolted directly onto the pressure plate to create a balanced adaptor.

When in thermal cutback, will the controller seem to 'waste' amps? I would imagine it would simply stop taking in current - correct?


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## frk2 (Jan 2, 2009)

Coley said:


> On my 72 volt setup with 12 volt deep cycle batteries, if I hit 66 volts I am in need of a charge.
> 
> My charger puts them up to 78-80 volts (surface charge) after a 20 amp charge cycle, (2 hours)
> 
> ...


Coley. Maybe your batteries are different. But I can hit 66v at 150Amps and then it climbs right back to 73-74 (or even 75 volts)

I have 6v 'deep cycle' batteries which seem to be holding up very well. They are quoted at 115Ah for 1Hr discharge. These are heavy, bulky batteries and pretty much take all the space inside my car.


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## frk2 (Jan 2, 2009)

GerhardRP said:


> Sounds like a real puzzle.
> Do you have a performance curve for this motor that you can share [spreadsheet or table is best]
> Could you make a few measurements:
> What are the current and motor voltage at full throttle launch from dead stop?...cold and hot.
> ...


Gerhard, I wish ADC would give me that. The only thing I have from the manufacturer is continuous rating at 6kw and peak rating at 16kw. I cant measure RPM which is the problem. But let me try to get you Speed vs Amp draw and voltage if I can.


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## Duxuk (Jul 11, 2009)

FRK2, are you sure your charger is giving you 100% charge. It sound as if your voltage under load is rather low. 66V is surely somthing you would see when the batteries are quite run down. I would suspect that your pack might not be getting fully charged.


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## CPLTECH (Sep 14, 2007)

frk2 said:


> My brakes are the only things that get REAL hot (the wheels and the rotor can go upto 70-80 degrees celcius) quote]
> 
> You say the brakes get real hot. Is it possible the brakes are adjusted too close so that just a certain amount of use causes them to expand even more? If that is the case, back them off some more. That would explain the increased amperage after driving a distance.
> 
> Altho there are 2 areas of concern as well, a small motor and 72V system. I use 250AH batteries in a 120V, 26HP system that consumes 120-150A. Keep in mind that a low voltage system requires much more amps than a higher voltage system to do the same work (HP) as defined by Ohm’s Law.


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