battery charge

[Deleted member 4366]

Most chargers are set to 42v (4.2v per cell). Most BMSs have bleed resistors on each cell. The resistors are switched on at a voltage slightly below 4.2v, so they slightly slow down the charging of the highest cells while still allowing the lower ones to charge at the full rate. When the first cell reaches 4.2v, the BMS switches off all charging, but the bleed resistors stay on until the individual cells drain down to about 4.1v. That's generally how BMSs manage balancing, which sorts out minor differences, but id the cell voltages are totally out of balance, it's not enoght. The same principle applies to LiFePO4, but the cell voltages are lower

 

[D C]

Forgive what may be a silly question but would it help to ride the bike till the battery fully discharged then put on charge for maybe a couple of days.
I'm just curious, don't have a problem myself apart from not knowing much about the electrical side of things.

 

[robdon]

I left it on charge yesterday for 9 hours, but unplugged it when I went to bed, put it back on this morning, will give it another 15 hours.
see what its like then, is at 39.5 volts at the moment, charger on green.
ROB

 

[robdon]

BATTERY BEEN ON CHARGE now for 15 hrs and has not altered 39.3 volts
on battery discharge end, charger giving 42.3 volts, at charging end of battery
38.8 volts.
I am going to bed now and see what happens next in the morning.
ROB

 

[robdon]

What next DAVE, would this battery power a bike and how long, or would it cut out, also it was advertised as 15ah is it.
I was just having some suspicions
ROB

 

[Deleted member 4366]

You have to balance the cells manually, which means a lot of monitoring. I have a £60 BC168 charger that can do it automatically, otherwise you have to charge one cell at a time with a single-cell lithium charger or drain the high ones down by connecting a bulb. if you use a bulb, you have to stop at the right point.

You could try this one. Cut off the connector and solder on two pins. You have to plug it in the right way round or it'll pop.

http://www.ebay.co.uk/itm/3-7V-500mA-Output-1S-Lipo-Lithium-Battery-USB-Cable-Charger-Red-JST-Female-Head-/301034539225?pt=UK_ToysGames_RadioControlled_JN&hash=item46170e88d9

 

[robdon]

I may be getting out of my depth, I had not seen a Li-ion battery till a few months ago never mind balance one, although I can solder and willing to try things, if it works in the end, the two bikes I have at the moment have good batteries, this one was to replace the one on a Giant suede, which is like new condition.
ROB

 

[jackhandy]

I've been meaning to post this for a while... Thanks to D8veh for the tip...
I use an oldish Motorola phone charger marked 4.4v 1.1a output, which brings a cell up to 3.6v & holds it there, sweet as a nut. (I know this because I forgot it was charging once & left it on overnight)
They, or something similar, should still be knocking about in bargain bins or car-boot sales.
I have 2 sons-in-law who bust phones regularly, so I end up with odds'nsods of chargers.

Cells are then popped into a Trustfire 2-cell charger (which won't charge anything below 2.7v) & it brings them to 4.2v.

 

[Deleted member 4366]

Don't worry. You're not getting out of your depth. It seems complicated when you read about it, but once you've done it, you realise how simple it is.

Imagine your battery is made of ten upright tubes of water, and each column is a different height from 3.8cm to 4.1cm. Your task is to make them level by putting in more water or taking some out. You have two rules: None must be allowed to go over 4.2cm, and none must be allowed to go below 3cm.

Any two adjacent pins in the connector represent one tube. Connecting a bulb is like pricking a hole in the bottom of the tube to make it drip. Using a charger is like dripping in water from the top.

That USB charger is probably automatic and will switch off at 4,2v, but you need to check by measuring the voltage from time to time until you can see that it turns green and stops at 4.2v. After you've cut off the connector, you have to check with your voltmeter which side is positive. Then make sure that it's the same way round as the red and black wires on the ribbon cable - red being the positive side.

You can use a bit of this stuff as a connector. Just break a bit off with 2 pins and solder it to the charger.

http://www.ebay.co.uk/itm/20pcs-2mm-40-Pin-Male-Single-Row-Pin-Header-Strip-UK-Seller-/400659509689?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item5d492af1b9

You can use any 5v phone or USB charger if you have a scrap one, but you have to monitor the cell being charged to stop it at 4.1v otherwise it'll go on to 5v.

 

[robdon]

how does the BC168 charger work is it difficult, and would it guarantee the battery worked proper, or could I just be throwing more money away,
this is a new batter did not arrive till mid November 2013.
I think I may have been done.
ROB

 

[robdon]

would I have to take the cells out of the battery, to do all this. these Motorola phone charger marked 4.4v 1.1a output are available on EBAY
ROB

 

[Deleted member 4366]

The BC168 will plug straight into the ribbon cable and do 6 cells at a time. You just need a piece of that pin-strip to go between the two connectors. We don't know how good your battery is until you try it. Some battery makers used recycled cells!

You don't have to do any more dismantling. All balancing is done through the multi-pin connector. If you're going to buy a charger, get the proper one like the USB one I showed you above.

 

[robdon]

so with the usb charger is it similar to checking the voltage on the 11 pin ribbon cable, and I could use a usb plug from the mains, also can they be obtained in the UK, I have had a camera from HONG KONG this week, took five weeks to arrive

 

[Deleted member 4366]

That USB charger is the proper one for the job. You can use any USB charger, Just cut the connector off and solder on two pins.

 

[robdon]

and use it on the BMS ribbon cable like when I tested the voltage, and do I bring all the cells to 4.2 volts
ROb

 

[robdon]

iv`e cut a usb cable their are four wires + shielding :red, black, white and green, I should think I use red and black and I have some pins to solder on.
I will use a 5v usb mains plug will that be ok.
ROB

 

[Deleted member 4366]

Looks like you've got it sorted. Aim for 4.1v. Be aware that the voltage rises increasingly more rapidly once you go past 4.0v. Before you plug in to the battery, check that the voltage is the right way round by using a meter just in cast the guy that wired the charger is colour blind. it wouldn't be the first time.

 

[robdon]

will I be able to check the voltage on the ribbon cable while it is charging.
I should not have to touch 5 or 6 cells because they were at 4.1 volts
ROB

 

[robdon]

I have made up the single cell charger, and tested same with multimeter
when I start, will I charge like in the drawing moving from cell to cell as each is brought up to 4.1 volts, or leave positive lead on the red wire, and move along the cells with the black one, also will I be able to test the voltage as I am charging the cells

 

[Deleted member 4366]

Yes, that looks fine. You can check the cell voltage while charging. If you double-up the two wires, you can leave your voltmeter attached, but if it's one of those where you have to rotate the dial to switch it on, it's best not to do that while it's connected.