PINNED - Lithium battery conversion/info

[Scooterman]

Terry, when you next charge your pack can you post a picture of the cell resistances, I'm just curious as I've never seen anyone elses.

If you don't know, at the top of the graph you click view, then cell restistance.

Thanks

[Burgerman]

If you crimped all those inter cell connections they will be all over the place probably. If not now, in a few months.

Also its normal for 1 and/or 8 to be high, because those cells also have long charge cables added into the measured data.

[terry2]

If you crimped all those inter cell connections they will be all over the place probably. If not now, in a few months.

Also its normal for 1 and/or 8 to be high, because those cells also have long charge cables added into the measured data.

All connectors was soldered. And being so small it was a pain
The balance wires was soldered to. Looks like I may have to re-do some?

Is it ok to discharge them for an hour or two, then recharge?

Terry, when you next charge your pack can you post a picture of the cell resistances, I'm just curious as I've never seen anyone elses.

If you don't know, at the top of the graph you click view, then cell restistance.

Thanks

Will do

[Scooterman]

Also its normal for 1 and/or 8 to be high, because those cells also have long charge cables added into the measured data.

I'm SO PLEASED you said that because 1 and 8 were slightly high and low and 2,3,4,5,6,7, were grouped together in a band. I didn't wonder whether it was due to something like what you mention, I'm glad you've cleared that up

EDIT: This is what I got, I hope they're okay. But the charge was done on the bench and as you say I will probably get problems down the road in the scooter if I leave them with crimped connections.

[Burgerman]

Unless you are charging like a hobby pack with 3 inch cables thats quite normal.

The cell resistance is lower than that.What you are really measuring is the charge cable and connectors mostly...
So unless one of them is drastically different ignore it.

Do you realise that 2mOhm is basically a loop of wire cable? Its extremely hard to accurately measure battery resistance at such low levels accurately. 2 milliohms is equal to just 0.002 of 1 ohm.

[Scooterman]

Wow, thank you BM that's reassuring. When I compared my measured cell resistance with the spec sheet for my cells, the spec sheet stated a much lower level, and I was worried I'd done something to damage the cells when my old PSU went up in smoke and the graph went a bit haywire, and I was still learning then so wasn't very confident in my knowledge. I'm more so now.

This is the charge from 3.5v to 3.6v. When I'd built the 2P8S pack, to get the cells to balance I had to charge each 2P cell group up to 3.5v, then hooked them back up as 2P8S and charged to 3.6v. And I was pleased they seemed to balance okay.

But I will redo the links before installing the two 12v packs in the scooter.

[steves1977uk]

Here's mine SM...

This is a 4+ year old pack made of Headway cells. Before I had it rewired and rebuilt, cell 8 would exceed 4mOhms the odd time. So you have nothing to worry about!

Steve

[Burgerman]

Is it ok to discharge them for an hour or two, then recharge?

Yes.

And if storing them, take out 1/3rd the capacity. So remove around 60 to 70Ah from a 180Ah pack.

[terry2]

Do they look good or will I need to rewire some?

I did discharge it for 2.5 hours, then recharged it.

[Burgerman]

Looks OK to me.

[Burgerman]

You put back 13Ah.
What Amp ws the discharge? Around 4?

How many Ah did you put back after the ride out?

[terry2]

Looks OK to me.

Thanks BM. My mind is at ease now

You put back 13Ah.
What Amp ws the discharge? Around 4?

How many Ah did you put back after the ride out?

I haven't got that info. I discharged it with the file you gave me.

But in the morning I will do my hospital run of just under 11 miles
And then I will take note of all the info.

Do you think I should get a fire extinguisher...

[Scooterman]

If you make a note of your mileage tomorrow, when you recharge you'll roughly know your Ah consumption per mile which should give you an idea of the range of your pack. Obviously allowing for a safety margin.

[Burgerman]

Do you think I should get a fire extinguisher...

Always wise. But they dont usually burn unless you hit them with some severe external heat. Anyway if it catches fire and you cant get out then you are likely to poo yourself. If its the right consistency that should put it out.

[Scooterman]

That was funny

I forget, you guys can't always get out of your chair quick enough or without assistance, so I can understand the concern. I would worried too!!! But as you say BM lifepo4 is pretty safe.

With lithium battery technology, is the fire risk only when charging?

[Burgerman]

With LiFePO4 its almost non existent. Shorting them, and stuff may burn wiring, and make a lot of heat and smoke but its not easy to get them to actually burn.

With LiPo or lithium ion they can do it because of manufacturing faults like the thousands of recalled phones, laptops, hoverboards etc. Or because overcharge. Or because you charge a pack then the temp changes. Or because they leak or get punctured and let oxygen in. Or just because they feel like it... And they go better than fireworks, and for longer.

[terry2]

Do you think I should get a fire extinguisher...

Always wise. But they dont usually burn unless you hit them with some severe external heat. Anyway if it catches fire and you cant get out then you are likely to poo yourself. If its the right consistency that should put it out.

My appointment was cancelled. So I went on a 6 mile spin at 6 mph. Went around a few shops.

Do I just charge it now and see how much it puts back?
Should I take pictures of anything first?

Thanks

[Burgerman]

Yes.

Went around a few shops.

That uses as much as your 6 mile spin.

[terry2]

Yes.

Went around a few shops.

That uses as much as your 6 mile spin.

Never knew that.
It's charging now. I will post graphs after.

[terry2]

Here is the graph

[Burgerman]

Well you used 21Ah. Out of 176?

Thats 176 div by 21 = 8.3. So you can go 8 times further than that.
So 8x your 6 mile spin and shopping is 48 miles. If you skip the shopping you can likely almost double that. But you should keep 10Ah in reserve. So call it 70 miles with 6mph running. You better take some packing up.

However, take a look at the inter cell connections when you can get chance. They should all stay relatively close together on that graph.

[terry2]

Well you used 21Ah. Out of 176?

Thats 176 div by 21 = 8.3. So you can go 8 times further than that.
So 8x your 6 mile spin and shopping. If you skip the shopping you can likely almost double that.

However, take a look at the inter cell connections. They should all stay relatively close together on that graph.

That's fantastic news

I will look at cells 2 and 8 when I can get someone to life the chair up for me.
Thanks again BM.

[Burgerman]

Also you may notice just 1 hour charge. You can knock 15 mins off that if you increase 30A to 40A charge.

[terry2]

Also you may notice just 1 hour charge. You can knock 15 mins off that if you increase 30A to 40A charge.

I will keep that in mind

Thank you to everyone for there help

[Scooterman]

Stirfry copper anyone? Seasoned with white wine vinegar and a dash bicarb.

I'm not too sure about the copper, it probably will oxidise but I'll stick with it. Hopefully any oxidization will only be on exposed surfaces and mating surfaces should be air tight??? Only time will tell..............................

And as far as the links go, they're still crimped only . I'm worn out and couldn't face stripping off the heat shrink and redoing them with solder, at least not until I get better at soldering.

The cable doesn't look very thick, 6mm^ stranded pvc, but it's in parallel (1/2 current per leg) and scooter only has one motor with a 42A constant current rating.

When I had the cells on the desk to test charge I used single 2.5mm^ series links, and the links didn't even get warm with a C-rate of 20A. The 2.5mm feed cable did but not the links so I'm confident 6.5mm^ parallel will be okay.

The balance nodes lugs will go on top on the copper nuts, and then nyloc nuts over the whole lot and a smear of vaseline (petroleum jelly).

Admittedly it looks a bit 'heath robinson' but it's my first attempt and if I was to redo it or do another pack for my powerchair I would make a better attempt. Just got to install it now and mod scooter wiring a bit, and bobs your uncle, fannys a rude word!

[Burgerman]

You want problems? Use bare copper... And crimp only. You see those copper studs and nuts in that strainer bowl? They are already oxidised.

Use plated (zinc) or stainless steel bolts, And tinned ring terminals soldered.

[Scooterman]

It'll be okay!

I know they did a little bit cos I left them too long. But I gave them another dose before installing

[Burgerman]

Nope, you will LIKELY get a graph that is all wobbly and uneven looking like cell imbalance. And if not at first, in a week or two.

[Scooterman]

We'll see.....

[Burgerman]

You wont know. Because uneven balance by a few mV looks the same as cell issues. So you will be in a dilemma...