My motor cuts out after 4 miles?

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praskal

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Joined
Dec 25, 2007
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60
Location
Corvallis, Oregon
I have a mountainbike with a rear X-Lyte 5 hub motor. I have six 12V 12ah SLA batteries (72V 12ah total). I recently got a new 40 amp immediate start controller. After about 3.5 to 4 miles of normal hybrid riding, the power suddenly cuts off. I have to wait a few seconds and it kicks back on for a few seconds. It then cuts out, and back on until I get home. This is really strange because even with my old 20amp controller would get me over 10 miles, even up a big long hill. I have pretty new SLA batteries. My voltmeter says all of them are ok. Is there something in the 40amp controller that is governing things or something??
 
I think you'll find it might just be the SLA voltage sagging right down due to the increased current draw. My experience of SLAs is that the voltage dips quite a bit under heavy load, so maybe they are dropping enough to trip the low voltage cut off on the controller. This seems a bit odd though, as I'd have thought that the LVC would be set pretty low if you're running 72V.

It could be that your SLAs could just cope with the lower current from the old controller, but not with the higher draw with the new controller. I'm wondering if there may be some sort of problem with the new controller cut off, may be the over-current circuit (which normally just current limits) is triggering a shut down. No doubt someone here with more detailed knowledge of the controller might chip in here.

Have you looked at the battery voltage under load? This would confirm whether or not voltage drop is the cause of the problem and might give some clues as to what's happening.

Jeremy
 
Try to measure the battery voltage under load to see if it's sagging too much.

A loose connection in the battery wiring can do the same thing. Sometimes a bad connection heats up over time then goes open. These will usually have obvious signs of heat damage.

Another thing that can cut out is the thermal sensor in the controller. Is the controller getting hot? When it gets above a certain temperature, it kills the output until it cools off.
 
1. Yes. The controller gets hot, which is odd because that new 40amp 72v controller is supposed to have the upgraded mosfets that are supposed to handle the current.
2. A battery certainly could be bad. I, however, have no idea how to do a load test. Do I have to buy some soft of load tester?
3. I will look at all the connections very carefully.

More to come...
 
If you can apply the brakes while running the motor, that will put a good load on it. You can do this with the wheel off the ground. Measure the battery voltage as close to the controller as possible to detect any bad connections along the way.

Hot controllers are bad. Even with upgraded FETs, they still give off some heat and need good air flow, but if it's getting hot with good air flow, that indicates some kind of problem.

Dragging brakes? Low tire pressure?
 
Well, I went ahead a bought a load tester. All of the batteries are fine. The problem probably is that, in my infinite wisdom, I had decided to place the controller underneath a gortex bag with the chargers and batteries. I guess my rationale was to prevent the controller from getting wet. Anyway, I have now move the controller to the outside so it will breathe and be windswept. I guess next time I ride I'll see if this works.

I wonder if I can find out if I have done irrevocable damage to it??
 
My guess is you haven't hurt anything. I tripped the overtemp several times on my cheapo brushless controller in the 100F heat around here. Since adding enough extra heatsinks to finally make it stop, I've ridden over 2000 mi with no problems.
 
is this the new V2 Crystalytle controller with the ribbed case? these have a LVC set much higher than the old analog controllers. the analog controllers were set to a 29V LVC (Low Voltage Cutoff) the newer V2 controllers are usually set for a much higher LVC.

when you say hot do you mean too hot to hold, too hot to touch or just really warm to the touch. remember that your hand could be quite cold because the ambient temperature is very cold. this would influence your judgment of how warm or hot the case really is.

rick
 
The bag would do it. The thermostat was probably doing its job so everything should be fine.

That's a bit of a dilemma to keep the thing dry, yet allow for good cooling. Water kills them for sure.
 
Ok,

I rode this morning 9 plus miles to work, with the controller
installed outside so wind can cool it. When I got 5.6 miles into it
the power cut off again. Of course, I had 3.5 more miles to go -
uphill. That's alot of weight to lug up a hill. It did the same thing,
on for 2 seconds, off for 2 seconds all the way up. And by the way, I
felt the controller many times and it was not hot to touch.

I know the batteries are fine, and that there is much more juice in
them. I disconnected the Cycleanalyst just to make sure that it wasn't
governing the controller. The power still cut out repeatedly.

This is a ride I used to do easily with my 35amp 72V controller. My
20amp 72V controller even did this ride without problem. I have to
assume I got a dud. This 40amp 72V controller really sucks. I have no
idea what to do.
 
What was the pack voltage on the CA when you were getting the cut outs? Was the voltage dipping much?

From the symptoms, it sounds as if you may have an intermittent fault in either the controller, the wiring or the motor. It might be hard to pin down the cause, but if you still have your old 20A controller you might try substituting that back in with the existing wiring, as a cross check. If the problem is not there with the old controller, then it does sound as if the fault may be in the new controller.

Jeremy
 
I just got home. I noticed that when it cut out is when the voltage would drop below about 55V.

Wow. This essentially means that I can't use the bike to go to work.
There's no way I'm biking up hill for over 4 miles. This morning I
really went very light on the throttle and I still had to pedal up
hill 3 miles.

So, does this mean that the old 35amp and 20amp controllers didn't
have a low voltage cut off?

Is there anything I can do?
 
Something sounds messed up.

The low voltage cutout should be lower than 55v. I guess it would be good to test exactly what the LVC is set at.

You could possibly try testing with the wheel up, use different taps on your battery pack to feed different voltages into the controller and see how low it can go and still run.

Perhaps the LVC is set too high on your controller. Since you have a CA, you don't even need the LVC in the controller. Mine are set at around 29v.
 
Dropping from 72V down to 55V is a pretty massive drop under load. Either the SLA batteries simply can't source enough current (most likely explanation) or there's a high resistance connection somewhere in the wiring between the batteries and controller. My money's on the SLAs not being able to source the high current that the new controller is demanding, pretty much as I guessed in my first reply.

It's interesting that the controller cuts out at 55V, I'd have expected it to be a fair bit lower. As Fechter says, they are usually set at 29V, as far as I know.

Either way it looks as if you need to invest in some batteries that will deliver 35A or so without a problem, as dropping around 17V under load seems way too much. Decent high discharge current SLAs will be OK, but the ones sold for standby operation won't, they'll struggle to deliver more than 1C - 2C without a fairly savage voltage drop.

LiFePO4 batteries seem to hold up well under load, provided you have a big enough pack, as do NiMH cells.

Jeremy
 
55 volts/6 batts = 9.16 volt per battery. Sounds right for a cutoff voltage for 72 volt controller. Lets see:

40 amps for these batterys = 8 minute run time. Way too many amps.
 
Sounds like if I really want to fix this problem then I need better batteries. The problem is that I can spend $100 to $120 for 72V 12ah SLA. For the equivalent in Li batteries would set me back $1000 for the pack and chargers at least. No way.

"40 amps for these batterys = 8 minute run time. Way too many amps."

I guess I should have gotten a lower amp controller. Shame to me.
 
Get a trailer and get 6 more sla's. Run in parallel. Maybe you can change the current on the controller to adjustable. Then you get 20+ minutes of run time. Maybe alot more. Depends if the extra weight will be counter productive or not. "Rassy" ran 9 sla's in a trailer at one time. You would have 12 plus the x5.
 
D-Man said:
55 volts/6 batts = 9.16 volt per battery. Sounds right for a cutoff voltage for 72 volt controller. Lets see:

40 amps for these batterys = 8 minute run time. Way too many amps.
Click to expand...

My new xlite 40 amp 72 volt controller cuts off at about 55 volts . I tried it on a 48 volt pack and the controller wont turn on at all. I run 20 sla 6 volt 14 amp hour battery's. I put the 40 amp 48 volt controller back on to use at 60 volts and my heavy pig goes 40 miles plus on a charge. I wish i would have never bought the 72 volt had i known it cut off at 55 volts. But thats my fault for not asking before i bought it.
 
sounds like you have the new Controller, which has the LVC set for 72v batteries, so at 55v LVC. the old style was set for anything above 36v batteries, so 29v LVC.

It also sounds liek you may have a bad cell in a few of the SLAs if they sag down to 55v under load. - They shouldn't be doing that.-

I used to run 12v 10AH SLA, and had experiance with a few going bad. Under load, and on a full charge, they worked perfect. but after 4ah had been drained off, they would collaps on them selves under load. The problem drove me nuts for weeks, because they would still test good voltage, and under a light load, like running the motor with the wheel off the ground, they would hold voltage and current. but underr full load of 30 amps they would fall off to 5-6 volts.

SLA don't always deal well with high current draw, so using the bigger controller may have been all they needed to die. you may get more life out of them if you can borrect the LVC to 29v
 
If my 72V 12ah SLA batts are not enough for the 40amp controller, then what exact batteries is this damn controller made to work with?

Maybe I should just go back to the old 20amp controller that actually worked.
 
praskal said:
If my 72V 12ah SLA batts are not enough for the 40amp controller, then what exact batteries is this damn controller made to work with?

Maybe I should just go back to the old 20amp controller that actually worked.
Click to expand...


Nicads are cheap and reliable. if you can find some cheap, 3c dischage Nicads, you would only need around 15ah worth to make sure you have enough for the controller. Since SLA are good for 150 cycles maybe, and Nicad can go 1000+ they more than pay for themselves. They're also 1/2 the weight, and 15Ah of Nicad would potentialy have twice the range of 12ah of SLA, due to SLA's pukert effect.
 
Which brand sla's are you using praskal?
 
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