intermittent cutoff

[djimme]

Hi everybody and thanks for all the tips. I just bought a 36v500w golden motor, hooked it into a 36v10ah lifepo4 battery (censpower), it works, but I got intermittent cutoff for a few seconds when I near 30, 35km/h and it's back again, throttle is not at the max. I was thinking to add more material on the shunts of the controller, could that help ?
Also to make it work I have to put the battery switch on, first and connect the cable after, it seems that makes the jolt that wake the controller (otherwise nothing).
Also at the beginning I tried to switch cable to make it work, red on brown (on my battery) that didn't work (blue worked), but I hope I haven't burned something inside.
Or could it be a resistance in the battery ?
thanks for any suggestions.

[erdurbin]

Are there 10 cells or 11 cells in your life battery?

If there are only 10, then you are probably suffering from voltage sag below 31.5 volts.
Since each cell only has 3.6 volts at rest, you have 36 nominal volts. you are really only getting about 33 volts after a load. 33 will drop down to 31.5 and below fairly fast under a 15-30 amp load.
If you have 11 cells you should not have any problem with voltage sag until you have ridden for a while (anywhere from 6-12 miles depending on terrain).
Also, if you have 11 cells and are still suffering from this, try checking the voltage of each cell because you may have one that is bad.

Let us know...

[OneEye]

I would have to agree it is probably the low voltage cutoff and the voltage under load of your pack.  If you search on the forum there is a thread about adjusting the low voltage cutoff to match the recommendation of different battery chemistries.

[djimme]

Hi good news, I did some soldering in the battery connector plugs, also change the length of the controller battery cable (now it's about 60cm thick as double size a computer power cable) and i'm on flat ground at max throttle. Speed, I didn't measure precisely but fast enough not to want any quicker in town (i think around 40km/h). But still experiencing cutoff when big wind, slope and after 10km or so.
Did go up and down Montmartre hill in Paris, very interesting experience I must say, fresh and clean at the top (me)...
Here's the specs of my battery (363usd with transport to France, I bought the motor without the wheel for around 150usd if my memory is correct), I think from the standard voltage that it's a 10 cell battery :
 Censpower battery :
1. standard voltage       35.2 V
 2. rated capacity       10Ah
 3.discharge voltage       40?0±0.3 V
 4.maximum charge current       1.5 C5A
 5. charge manner       CC/CV ?constant current/constant voltage?
 6.maximun discharge current       3C5A
 7. end-off voltage       22±0.05V (singel)
 8.operation temperature
       charge?   0?  - +45?
       discharge?  -20? - +60?
 9. store temepature       one month? -20? - +60?
       three months? -20? - +45?
      one year? -20? - +25?
 10.relative humidity      65±20%
 11. weight      approx4Kg
 12. size(mm)      L:92  W: 88    H:385

Target of charger?
input? Ac 220V
output?44V  1.8A

So I read the post on the cutoff voltage and I say "bravo" for your findings, do you think 1.5 resistor is the way to go for my battery ? and is the resistor this one, see pic pink arrow. Also as electronic is like magical talk to me, can I do that with a common soldering tool with a small tip ?

[djimme]

some pics... for the cable lenght i'm not sure it's the best, i'll ask my seller.
 

[erdurbin]

Can someone post a really good close up picture of where to replace the resistor. I have a LiMn pack that would probably go down to about 28 volts and still be ok, if not even less. I would really love to change out my resistor, and have looked at the other posts, but just want to make sure I do it correctly.

[djimme]

end-off voltage 22v must be the lower my battery can go right ? In doubt i'll try a 1.5k resistor anyway since i'm almost at max throttle already. i'll let you know if i've fried my battery

[pdonahue]

Can someone post a really good close up picture of where to replace the resistor. I have a LiMn pack that would probably go down to about 28 volts and still be ok, if not even less. I would really love to change out my resistor, and have looked at the other posts, but just want to make sure I do it correctly.

Hi guys,

This is mostly repeated info from the earlier thread, I'm attaching two images here.  The first shows the whole board, the second is a close up of the three resistors.  (This site only allows 128kb images.)  The green arrow points to R73, red to R4, blue to R11.  The cutoff voltage is:
3.1 * (R73 + R4 + R11)/R11
From the factory, the values are:   R73=11000,  R4=0, R11=1200 for a cutoff of 31.5V
The cutoff gets triggered when the connection between R4 and R11 reaches 3.1V.
To increase the cutoff voltage you can increase R73 or R4, or decrease R11
To decrease the cutoff voltage you can decrease R73 or increase R11     (R4 is already at zero)

Thanks to djimme for letting me know that this thread was here.  I've pretty much put my bike away for the season now since the temperature got down below freezing in the mornings so I haven't been checking in on this forum much. 

Have fun,

Pete

Pete

 

[djimme]

Ok so I changed it like pete said, the r11, 1201 ohm resistor with a bigger (lot bigger in size in fact) 1.6k resistor and... it WORKs like a charm. no cutoff, on slope or against the wind... real cool. Thank you everyone for your help.
 

[erdurbin]

This is great! I'm next...

Probably a dumb question, but where would be the best place to get that resistor?
Also, what wattage does the resistor need to be. I think I found a local place that sells them in a pack of 3, but they asked what wattage I needed.

[OneEye]

Awesome it works for you.  Sure sounded like a low voltage cutoff setting that was too high for your pack.  You should have a better overall range now as you are able to use all of your pack's capacity.  You may want to use a digital voltmeter to measure the voltage on the pack and ensure the LVC is kicking in at your calculated value.  The LiFePO₄ packs have a wonderfully flat discharge curve, but they fall extremely quickly at the end of discharge.  I'm actually a bit surprised the manufacturer is recommending a 22V cutoff.  Some of the other users of 10 cell LiFePO₄ packs are using 25V, just as a bit of a safety cushion.

erdurbin:  For a single resistor, it may be just as cheap to buy a pack of 5 at your local radio shack as there will be no shipping fee.  If you have another electronics project in mind you may want to order through digikey or mouser.

[erdurbin]

Looks like Radio shack has a 1.5k in a 1/2 watt. Is this ok?

http://www.radioshack.com/product/index.jsp?productId=2062324&cp=&pg=3&sr=1&origkw=resistor&kw=resistor&parentPage=search

[pdonahue]

This is great! I'm next...

Probably a dumb question, but where would be the best place to get that resistor?
Also, what wattage does the resistor need to be. I think I found a local place that sells them in a pack of 3, but they asked what wattage I needed.

Any electronics store will have them.  Wattage doesn't matter (there will be very little current flowing through them) but I think the one in there is a 1/8 or 1/10 Watt which is smaller than anything you'll be able to hand solder.

Pete

[pdonahue]

Looks like Radio shack has a 1.5k in a 1/2 watt. Is this ok?

http://www.radioshack.com/product/index.jsp?productId=2062324&cp=&pg=3&sr=1&origkw=resistor&kw=resistor&parentPage=search

That should work fine.

Pete

[pdonahue]

   (R4 is already at zero)

...humm. Hold up a minute... to retain factory settings how about cutting the R4 trace and adding a 1.5k or even a 1.8 pot since decreasing cutoff is the more likely direction? This way you can experiment/adjust the setting with a voltmeter for whatever pack you use, excluding SLA/AGM of course. A two position external switch for zero resistance and 1.5k to replace R4 would be great as well. Never know when you might need those SLA/AGM's to go back into service.

Putting a resistance across R4 will increase the voltage.  But, your idea would work if you just replace R11 with a pot instead of R4 (more of a wire than a resistor really).  In fact, with pots replacing R4 and R11 it would be possible to go up or down.

Pete