22A Controller with 20A battery - fuse blows on hills

[jamie]

Hi

I recently added an e-bike kit to my bike... all was going well until today I thought I'd test it on a long steepish hill. After about 10 minutes of going strong everything suddenly died!

Found that the 20A fuse in the battery had blown.

I note that the controller is a 22A limited Nine Continent one. I'm guessing the controller was drawing the full 22A from the battery on the hill.

If I replace the 20A fuse, is there any way to limit the controller to 20A to avoid blowing the fuse?

If I replace the fuse with say a 25A fuse, will this harm the battery if the continues to draw 22A? (I'm assume the battery is rated at 20A) Or would I get away with it occasionally?

I don't regularly ride up long hills, but it would be good to be able to do so occasionally without blowing a fuse!

Also, should I replace the fuse with a slow or fast blow type?

Thanks
Jamie

 

[dogman dan]

A 20 amp draw can easily ruin a cheap low c rate 10 ah battery. ( one that should never see more than 15 amps) So assuming you have something tiny, the answer is yes, you have the wrong battery for your motor and controller, and no fuse can help you.

Let us know what you have, so we can write an answer that is not a speculative guess. I'd put a 30 amp fuse there, if you have a good battery for the motor/controller.

 

[jamie]

Hi

The motor is an 8FUN BPM 36V350W.

The controller is a Nine Continent 36V/22A

The battery is a LiFePO4 36V/12aH. Has a 20A fuse. I don't know exactly what brand or model, but going by pictures it appears to be a Herewin brand.
If correct it supposed to have a working discharge of 5-20A and claims to pass the followng test:
over charge
over discharge
short circuit protection

Considering it supposed to have over discharge protection, do you think it would be safe enough to use a larger fuse (basically for short circuit protection)? Or do you think the the 20A fuse is part of the over discharge protection system?

Also should I get a slow or fast blow fuse?

Thanks
Jamie

 

[dogman dan]

I don't think the type of fuse matters too much. What matters is that your battery is likely to have a c rate of 2c. That means any amps over 24 amps is damaging it if done for very long.

It also means that to get the maximum lifespan from the battery, 1.5c should be about your max amps. That's 18 amps. You have a 22 amp controler, and under the right conditions it may be able to supply 25-30 amps for a brief moment.

So in my book, you have a controller that will kill your battery earlier than a 15 amp one would. As I said before, no higher amp fuse will save your battery. Only your throttle hand and pedaling your ass off on the hills will do it. To clarify, you gotta try not to ride in a way that blows that 20 amp fuse. Idealy you'd never exceed 18 amps of draw.

You won't have a problem with full speed travel on the flats. 20-25 mph is only going to take 15 amps, so that will be fine. You might try carrying a lot of 20 amp fuses, and train yourself not to blow them. Pedal at starts, and use less throttle and more pedaling on hills.

If you have some money, a new 15 amp controller will be one hell of a lot cheaper than a new battery. Tools help you adjust your ride as well, any kind of amp or watt meter will help you learn to ride using less amps. A cycleanalyst is the ideal, but even a cheap crude automotive 12v ampmeter can work to let you know if you are using 10 amps or 20. In between, there are wattmeters that cost less than $100.

 

[dnmun]

can you post up a picture of your battery? is it made up of dozens of small cylindrical little AA sized batteries?

is it a pouch type or does it have larger cylinders?

do you have a voltmeter yet?

does the battery BMS shut off the battery when it gets totally discharged?

i like those infineon controllers so i would keep it

they may have put the small fuse there because they decided that was the best way to stop you from drawing too much current, but it may just be an accident, and they only had 20A fuses in the box when they made your battery.

you do need a wattmeter or cycle analyst to make it easier to manage the discharge of the battery. you need to know how it performs and when it starts to have problems.

if your BMS does actively shut off the battery, then why not just remove the fuse altogether and solder the power wire together where the fuse is now. then use the wattmeter to maintain some awareness of how hard you work the battery.

 

[jamie]

Hi

I'm pretty new too electric bikes. Don't have a cycle analyst or watt/amp meter. I do have a digital multimeter, if that is any use?

I haven't opened up the battery to see the innards.

I'm waiting to hear back from the guy who imported the kits, not expecting a reply till Monday. Hopefully find some more info on the battery. He was not intending to give me that controller, but he couldn't get pedal assist to work on the controller he got specially for me. I wanted pedal assist as I have drop bars and wanted a pretty simple setup when I just pedal and go. Up until the hill it has been just want I wanted.

The main picture picture of this product listing looks exactly like the battery case. It is rack mounted battery with battery locking:

http://herewin.en.alibaba.com/product/350476542-200207542/good_price_36V12AH_long_cycle_electric_bicycle_polymer_lithium_battery.html

The other pictures in the same page don't look like the battery. They also show a flat pack type of cell, dunno if that has any relation to the actual battery!

Just uploaded a couple photo of the battery on the bike... probably not much help! Will post specific details of the battery when I get them.

Thanks

 

[d8veh]

It looks like 1C LiFePO4 cells, so the battery would be rated at 12 amps with a max discharge rate of 20 amps. If you fit a higher rated fuse, the BMS will probably start tripping, so it would be better to limit the current. There.s a thread on how to change current limit here:
http://endless-sphere.com/forums/viewtopic.php?f=2&t=37068
A more amateurish way to adjust the current is to file/Dremmel the shunt to reduce it andcoat it in solder to increas it. These things are very simple to do and don't cost anything, but you need a wattmeter to see the results.You can use one of these wattmeters for testing. Run the motor with the wheel off the ground and apply the brakes until the motor nearly stalls. Don't do it for long because the motor will get hot - just long enough to see the maximum amps.

http://www.ebay.co.uk/itm/60V100A-Battery-Checker-Balancer-charger-for-Voltage-Power-Watt-Meter-Servo-Test-/130731639478?pt=Radio_Control_Parts_Accessories&hash=item1e703682b6
or these
http://www.ebay.co.uk/itm/Multi-function-Wattmeter-FD-WM-/130665849560?pt=Radio_Control_Parts_Accessories&hash=item1e6c4aa2d8

 

[dogman dan]

20 amp fuse is correct for that battery for sure. By 20 amps, you do want it to positively stop. The guy should never have given you a 22 amp controller in my opinion.

But I've seen others sell similar batteries with 22 amp controllers. By the time problems develop, a warrantee period is over with. Those cells might be rated 2c if lifepo4 or even 3c if it's limn, but ratings are just guidelines and many here will de rate a claimed c rate, when the user is intending the thing to last a long time. So a 3c cell becomes a 1.5c in real world use.

Again, 15 amps is pretty close to your reasonably safe maximum amps with most batteries of that type, in that size. It can take a few moments of more, but a long hill climb at 19 amps could be damaging it. It might be possible to adjust your controller for lower amps, but I'm not expert enough to tell you exactly how. Never using full throttle up a hill again would be one way. Half throttle and pedal hard should help.

 

[dnmun]

those batteries appear to have a BMS inside so it will limit the current draw. you do need a wattmeter though, see if it will get really hot if you use a 25-30A fuse and if the BMS will shut it off before blowing the fuse.

but you should order one of these:

http://herewin.en.alibaba.com/product/520983535-213166108/10_2_2_android_tablet_pc_with_built_in_wifi_MP3_camera.html

 

[999zip999]

What ?

 

[dogman dan]

Surely he meant buy a wattmeter.

 

[dnmun]

no, i was hoping someone would buy that chinese ipad. i wondered how much it would cost. those guys also sell 5Ah and 10Ah lifepo4 pouches like ping's, and they have a buncha lipo RC packs too.

 

[jamie]

Hi

The guy I got it from seems sure the battery is rated at 2C, but a generic case has been used with a fuse more suitable for a smaller pack, but they haven't upgraded the fuse. He's also going to get specific manufacturer details on the cells. He is also going to source some 30A fuses and will send me one since the largest fuse I can find locally (in the 20x5mm size) is a 20A.

So will give that a go and see if the BMS gets tripped on the hill.

95% of the time I'll be riding on the flat, so it is not a huge issue with potentially killing the battery prematurely. Unfortunately I can't use half throttle on the hills as I've only installed the pedal assist sensor, as it was hassle to try and mount the thumb throttle on the drop bars, and I didn't want any clutter, or become lazy either, so unless I pedal really slowly (which isn't going to be practical on the hills), it will always going full throttle. Can't really be bothered with the hassle of an amp meter if I don't have further issues, and if the battery ends up lasting a few years. If it dies sooner, but not within the warranty period, then I'll hit him up to supply a larger replacement battery at cost. Probably a better solution as I like the performance the current controller provides.

Thanks

 

[dnmun]

you are not gonna kill the battery. it is just too small a fuse. you do wanna use a wattmeter, and you have to have a voltmeter.