58V on a 48V controller.

[iJim]

Hi all,

I've got a 48V front wheel hub motor and controller (a cheapo conversion kit). I've been running it for a week or so with two 6S 6.8AH lipos in series. Fully charged this gives 50.4V which drops down to ~45V within a few minutes of use. I guess this is pretty normal for the lipos, but the controller is expecting 48V and the low battery light is on most of the time (which means I have no warning if the batteries do drop low, which would not be good!).

I could add a third battery, I've a 2S spare. This would give me a fully charged voltage of 58.8V, would this be a problem for the controller? The controller is a generic Chinese model, no obvious part number or manufacturer (the label only says 48VDC, 27A).

Cheers,

Jim

 

[anotherkiwi]

Normal you don't have enough Amps. My 37 V 20 Ah nominative lipos drop from 41.x V hot of the charger to 38.5 V after 50 km of hilly riding...

 

[awol]

the low battery light is on most of the time (which means I have no warning if the batteries do drop low, which would not be good!).

You need to get a couple of these cell monitors to plug on.
http://www.ebay.co.uk/itm/RC-Lipo-Battery-Low-Voltage-Alarm-1S-8S-Buzzer-Indicator-Checker-Tester-LED-UR-/401183519955?hash=item5d6866b4d3:g:e0sAAOSwTZ1XmJgZ

 

[Nealh]

27amp controller not surprised the lipos only last minutes, which hub are you using geared or D/D.
You probably only get 10/15mins max, bare minimum will be 42v but to be a bit safer 43.2v.
As awol say's a couple of alarma or wire in a watt meter.

 

[iJim]

Not sure what type it is, looks like the 1000W version of this:

http://www.ebay.co.uk/itm/26-Front-Rear-Wheel-Electric-Bicycle-Motor-Kit-E-Bike-Cycling-Hub-Conversion-/322364987166?var=&hash=item4b0e73571e:m:mfK_XRNN_lMbUi9KjiF4xRA

I don't expect the 6800 mAh batteries to last long, but I thought I would test it out first and then invest in another 2 x 6S to double my capacity.

BTW, I have a couple of those cell monitors, the problem is they are so unreliable. Fully charged 6S battery showed voltages ranging from 4.32 to 4.02... yet my multi meter showed they were almost all bang on 4.2 +/-0.2.

Cheers

Jim

 

[Nealh]

The black one's from hobby king are better and are within 0.05 - 0.1v . They are worth having because once you are down to 3.5/3.6v there is little capacity to use, the bulk of the capacity is between 3.65 to 3.95v.

 

[Deleted member 4366]

Something is wrong with your lipos. They shouldn't drop to 45v. They must be totally worn out or just not up to the job. I end my journey when i see 45v on the voltmeter. I'd be interested to see what's on the cell monitors when the packs are under load.

 

[anotherkiwi]

Try 4 of these in 2P2S, for £200 including cables you will have a 44.4 V 16 Ah battery that will last +1000 cycles according to the drone guys.

https://hobbyking.com/en_us/turnigy-graphene-8000mah-6s-15c-w-xt60.html

 

[awol]

I end my journey when i see 45v on the voltmeter..

Is that with 12s or 13s ?

 

[Deleted member 4366]

Is that with 12s or 13s ?

12S. Once lipos reach nominal voltage, they start to accelerate downwards - that's 44v for 12S.

 

[iJim]

Well today I did a five mile round trip, full throttle most of the time and a relatively steep hill to get up. I had cell monitors on both batteries throughout with the alarm set for 3.2V, it never went off.

The voltage dropped quickly to 3.8-3.9 per cell but stayed almost constant at this level for the whole journey. Was hard to check the cell monitor whilst riding so I'm not sure how far the voltage drops under load. As the alarm never went off I guess it's ok for now!

Cheers all,

Jim

 

[Deleted member 4366]

3.2v is too low. 3.55v is about as low as you should go. By the time the alarm goes off, your packs could get bricked. There's virtually no charge between 3.2v and 3.5v, so they fall straight off a cliff when discharging. Look at the black line on this chart, which is closest to yours:

 

[iJim]

Yikes... Annoyingly, 3.2v is the highest voltage that can be set on the alarm!

Perhaps a solution would be to mount a cheapo volt meter somewhere on the bike that I can see when riding, that way I can keep my eye on it. 43v/12 = 3.6ish v per cell, I'll also be able to see what happens under load.

 

[Nealh]

Get some new alarm, all of the one's I've had/have can be set from 3.2 - 3.8v.

 

[anotherkiwi]

https://hobbyking.com/en_us/hobbykingtm-cellmeter-6-lipo-life-li-ion-cell-checker-alarm.html

This is a flimsy thing so it needs some protection but it does readings to x.xx V, mine are set to 3.65 V but I generally just read the overall voltage of the LCD-3 screen and when it drops to 36.5 V I stop and change batteries or limp home on pedal power.

 

[awol]

Perhaps a solution would be to mount a cheapo volt meter somewhere on the bike that I can see when riding

A voltmeter won't be waterproof, or the cheapest solution.
I've got one of these taped to my handlebars.
http://www.ebay.co.uk/itm/WaterProof-Mini-DC0-100V-Voltmeter-LED-Panel-3Digital-Display-Volt-Voltage-Meter-/142059824228?var=&hash=item21136ce464:m:mMn4cvjsojj9O_UuRNY2iww