Odd partial loss of power – confused ?!

[KirstinS]

I’ve been running my 250w 8fun motor with Ku65 controller on 44.4 volts (36v bottle battery and 7.4v booster battery) for some time with no issues.

I charge up my batteries, plugged them in and set off for my commute today. Totally gutless and no speed. Hmm. Only 1 bar on the 4 bar handlebar unit. Very odd as its designed for 36v so should show one bar when at around 34 or 35v ish. Given I’ve been running 44.4v ive not seen the bars go down ever !

I turned around and went home. Checked both batteries on the multimeter – 41.9v on the bottle and 8.10 on the booster. All seems well there (I knew booster was not quite full)

Plug everything back in. Same thing

Decided to go to work anyway and batteries seemed fine so should be ok(in my head anyway 

So for the full 7 miles the bike never went above 15mph and extremely gutless. A puff of headwind would slow it down. The handlebar showed one light throughout and my lipo alarm never went off.

I have run my KU65 on 36v and also 44.4v. At both voltages it goes faster with more torque. Around 22mph and 18mph at 44.4v and 36v respectilvy hot off charger reducing by up to 4 or 5mph when nearly empty.

The bike is behaving for all the world as if both the motor and handlebar panel are getting about 34v-sih – where has my other volts gone ?!

I’m at work so no multimeter  I will test everything at home but just wondered if any ideas ? I thought a dodgy connection would give either on/off. Or possibly reduce the amps where a connection was barely made.

But I didn’t think dodgy connections lost volts which makes me concerned its something more serious ?

Any help, thoughts, experiences appreciated !

 

[Deleted member 4366]

You did plug in your booster the right way round to add volts rather than subtract?

 

[KirstinS]

I just checked and, um, well, er, maybe I did just a little bit

What a first class numptey I am !

*bangs head on desk*

Thanks for help ! Likey to do any damage ?

 

[Deleted member 4366]

I think you just invented the battery tamer - for those that find their bikes too powerful.

I don't think you did any harm (other than to your reputation) ROFLMAO.

 

[KirstinS]

The Battery Tamer - love it. A solution to a problem that doesn't exist

I'll get it onto kickstarter right away !

And "my reputation grows with every failure" George Bernard Shaw

 

[KirstinS]

My idiocy does seem to have damaged the booster pack. Not , I guess , severely but each cell pack will only charge to 3.85v so the capacity appears reduced

Not really an issue but I post just for possible interest of those who understand these things ,

 

[Deleted member 4366]

Thinking about it, the batteries were fully charged when you connected them, and all the current flowing through the booster pack when you rode the bike like that would've gone in the charging direction, so they would've got over-charged. Maybe you were lucky that they didn't explode. When you measured them after the ride, were they still 8.2v?

Lesson to learn for your homework tonight (test tomorrow): Use connectors that can only be connected one way.

I've got some more cells if you need them, but you'll have to pay the postage because it was quite expensive last time.

 

[KirstinS]

Thinking about it, the batteries were fully charged when you connected them, and all the current flowing through the booster pack when you rode the bike like that would've gone in the charging direction, so they would've got over-charged. Maybe you were lucky that they didn't explode. When you measured them after the ride, were they still 8.2v?

Lesson to learn for your homework tonight (test tomorrow): Use connectors that can only be connected one way.

I've got some more cells if you need them, but you'll have to pay the postage because it was quite expensive last time.

I cant remember now - nothing abnormal, around what i'd normall expect at end of my 7 mile commute (one way) so around 3.9 or 4v per cell.

lucky escape then - and yes, you are so very right about the homework !. Its one I already knew and had originally made the pack so that you could not get it wrong. Then I made a repair to a damaged cable and put the connectors back on wrong. I knew I'd done but thought whatt he heck - I would never do anything so stupid anyway. I have done 200 lines "I must not be lazy and take shortcuts!"

Thank you again for the offer of cells. Really very kind. However, I think now that you shown me the way once I should try source them myself. I do actually have an 11.1v pack given to me by another member, manalog. So I can reconfigure that to 7.4 for time being - i'm not in a rush is what I mean. I like to try and do it for myself this time.

Been looking on ebay at job lots of laptop packs for speares or repair. I thought I could strip out the bare cells, test them on the imax b6 charger. Then solder up a pack of the matching ones in terms of voltage they'll charge too and mah capacites.

If you have any other top tips on sourcing these 18650 cells then always grateful. It looks like sellers seem to batch up by brand ( eg Dell or Lenevo or Acer packs) So if you know one brand to be better than an other then thats also very helpful to me

 

[Deleted member 4366]

The last lot I got were all the same type, but had been tested, so many of the cells were dead. I got about 30% good cells, which was about 25 cells for £11, so not too bad. Look at the photos carefully to see if the batteries have any markings to show that they've been tested. The previous two lots I bought hadn't been tested, and nearly all the cells were good, but there were too many different types. The newer the batteries, the higher the aHs of the cells. It's a bit of a lottery what you get, which adds to the fun as you crack open each pack to see what's inside.

AS long as the cells aren't down to zero, you can revive the low cells enough to charge them by using one good charged cell with two wires soldered to it. You can either hold the wires on to the low cell for about 10 secs or hold it in parallel while you start the low one charging, and then take it away. Don't try and charge any 0v cells and make sure that the charging voltage is limited to 4.2v and use low current to bring any low ones up.

 

[KirstinS]

Thanks d8veh

 

[KirstinS]

Found a friendly local repair laptop repair shop

I just walk in off the street , told the chap what I was doing and he gave me a bag full of old packs( about 15 )All untested and stripped out busted laptops

All for free ! And said pop back again and he'll give me more

Nice

 

[Deleted member 4366]

Excellent result. Before you strip the cells out, check the label. It nearly always says the maH and the voltage, which should give you an idea of how many cells and how many maH each. Aim for cells over 2000maH. A lot of older laptops have cells as low as 1000maH, which aren't much use.

 

[KirstinS]

Your right - every pack has the voltage but some quote wH instead of aH

From a quick google I think it goes like this

11.1v 48wh is 48 /11.1 = 4,324mh per series. So if 2 cells per series then great as roughy 2150mah per cell. But if 3 cells then not so good at 1440mah each

Is that about right ?!

Also is there really any difference between 10.8v and 11.1v Packs ? Just seems odd that lithium don't hold to a standard - some 3.6v nominal and some 3.7v

Have to wait till weekend to crack them

 

[Deleted member 4366]

Your calculations are correct, I'm not sure about the different cell voltages. In practice, these cells don't have a voltage because they go between 3.0 and 4.2. Normally the individual cells have the designation written on them, so you can look up the datasheet. You only need to do the calculation to figure out which packs to crack open first.

 

[Scimitar]

Found a friendly local repair laptop repair shop

I just walk in off the street , told the chap what I was doing and he gave me a bag full of old packs( about 15 )All untested and stripped out busted laptops

All for free ! And said pop back again and he'll give me more

Nice

Excellent work, Batman.

 

[KirstinS]

Update - all cracked and tested

Have about 50 good cells vs 12 duffers excellent ration as far as I'm concerned )

All 2000mah minimum some LG ones are 2500

Most are 2200 Samsungs

Question - any way to test actual capacity other than painstakingly one by one using the IMAX br6 discharge capability ?

Thanks