LiFePo4 for Permobil C500S

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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 17 Jul 2019, 14:10

2 hours CV not 2 hours charge. So yes. As long as all cells are full before assembly. So that balance should not take long. And OK for subsequent charges.

You can reduce to 25 no problem.
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 17 Jul 2019, 18:00

Does 'LiFe Charge ONE 90 to 200Ah Cell' terminate charging automatically?
Can I just start and no worries?
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 17 Jul 2019, 19:29

Yes, it terminates. I just checked it.
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 17 Jul 2019, 20:37

I got this graph:
Cell_1_charging_graph_20190717_2.png
Cell_1_charging_graph

Initial voltage was 3.300V.
I measured voltage after charging - 3.430V.
Why it's 3.430V?
Charger has to charge cell to 3.6V.
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Re: LiFePo4 for Permobil C500S

Postby Irving » 17 Jul 2019, 21:48

quadcopter wrote:I got this graph:
Cell_1_charging_graph_20190717_2.png

Initial voltage was 3.300V.
I measured voltage after charging - 3.430V.
Why it's 3.430V?
Charger has to charge cell to 3.6V.


An it did charge to 3.6v if you look at the graph. But as soon as you take them off charge the voltage drops back a small amount.
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 17 Jul 2019, 22:04

What matters is that it is charged at 3.55 to 3.60 volts and held there until it is charged. That point depends on the termination current, and balance on a full pack.

The voltage does not tell you anything useful. For e.g. 3.3x volts may be 98% full, or around 75% empty. Forget about voltages,battery meters, etc. Unless it drops below 3V and then you better not go any further.
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 19 Jul 2019, 12:15

When I charged at 30A the Revolectrix cable (12AWG) was warm and fuses were hot.
Cellpro PowerLab, Stackable, 40A Safety Banana Plug Cable.png
Cellpro PowerLab, Stackable, 40A Safety Banana Plug Cable
Cellpro PowerLab, Stackable, 40A Safety Banana Plug Cable.png (75.49 KiB) Viewed 1158 times

Anybody who will use same cable be careful with it.
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Re: LiFePo4 for Permobil C500S

Postby Irving » 19 Jul 2019, 14:36

quadcopter wrote:When I charged at 30A the Revolectrix cable (12AWG) was warm and fuses were hot.
Cellpro PowerLab, Stackable, 40A Safety Banana Plug Cable.png

Anybody who will use same cable be careful with it.

But even @ 40A is still below 100degC according to my IR thermometer and the silicone sleeving is good to 200degC. However the clear plastic sleeving around the fuses has gradually unravelled after 3 or 4 charges leading to a shorting risk, so be aware.
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 19 Jul 2019, 15:04

I cant say because I skipped the fuses. But the cables are fine at 40A.
And at 50. Direct from power supply when doing a top up next to my PC. Yes they get hot at 50A. But they are silicone cables and designed for that.
The stock fuses may get hot. But are rated for 40A continuous so SHOULD be fine.
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 20 Jul 2019, 16:23

I charged cells. Capacity IN about 95 Ah for every cell.
Then I assembled and installed pack.
IMG_20190720_123637_small.jpg

IMG_20190720_135749_small.jpg

I used original intersection between 4 and 4 packs (it's 8 AWG and it's part of circuit breaker).
I checked overall voltage (25.4V as I remember) and voltages on balance cables (every next = previous + 3.2V).
I started charging with 'LiFe PO4 1S 8S Approx 150Ah.PS8'. It took about 30 min to charge (balance) them.
I tried to run around. Works fine.
Tomorrow I want to run several km.
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 20 Jul 2019, 17:35

Are they 176Ah cells?

You should be able to go a lot further than that! Around 4.5 times as far as with lead, and still have some left.

One thing.

What is UNDER the cells?
What is between each cell?
The cells casing and bottom are not isolated,they are connected to the cells negative terminal. So every cell can short circuit and cause mayhem, heat, smoke, and huge problems if they touch electrically.

This matters! Under neads some thin plastic or non conductive sheet underneath. Also between every cell. Nothing must touch! Or :ambulance
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 20 Jul 2019, 17:53

Ops... between these three cells nothing (just original blue film/lamina).
So I need rework it.
But I looked at many packs with aluminum case without anything between cells.
How do they use them?
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 20 Jul 2019, 18:48

Extremely dangerously, they just dont know any better. Also the bottoms. Flat sheet of gasket paper, or rubber car mat, or stiff plastic card or something on the battery floor first. You dont want fireworks. 1000s of amps and things melting. Even if they dont burn, the rest of the wiring, chair does etc .
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 20 Jul 2019, 19:03

Is it enough do something like swalker?
Attachments
20190328_163529.JPG
Isolation
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 20 Jul 2019, 19:42

As long as no sharp edges anywhere and some rubber/nylon/pvc thin tough mat on the floor.
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 21 Jul 2019, 20:53

Burgerman wrote:some rubber/nylon/pvc thin tough mat on the floor.

Can it be silicon mat for baking 1.5 mm thickness?
silican_mat_bakery.jpg
Silicon mat for baking
silican_mat_bakery.jpg (21.56 KiB) Viewed 1092 times
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 21 Jul 2019, 23:20

Its not tough enough to stop spikes but if the floor is flat yes.
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 30 Jul 2019, 08:28

I tried to discharge one cell and in a several seconds got fail message - the voltage is bellow 2.9.
Charger stopped.
What does it mean?
Before this the cell was charged and capacity in was 95 Ah. voltage was 3.3V.
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 30 Jul 2019, 08:33

It can mean many things.

Was the cell FULLY charged. If not why are you discharging it? 3.3V tells us nothing useful. 3.300V or 3.350V is more helpful.

OK
if you have a bad connection to the cell, the charger sees a low voltage as it discharges. Lower than the cell.
If you have a cell that has bee over charged, or over discharged in the past, or that has failed for other reasons, it can have a fully charged voltage when unloaded, but drop to below x volts under load due to very high internal resistance. Just loke a bad connection.
If you have thin long wires, same thing, high resistance.
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 30 Jul 2019, 08:56

Burgerman wrote:It can mean many things.
Was the cell FULLY charged. If not why are you discharging it? 3.3V tells us nothing useful. 3.300V or 3.350V is more helpful.

I charged all cells with PL8. All got about 95 Ah in (except one - it got only 36Ah). All cells had 3.300V or 3.299V before charging.
I want to see how many current it can give out so ran discharge.
Now the cell has 3.371V.

Burgerman wrote:if you have a bad connection to the cell, the charger sees a low voltage as it discharges. Lower than the cell.

I use alligator clips. They have small connection area and thin cable.
I'll try something other. Hope it will help.
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 30 Jul 2019, 09:57

You need a solid tight connection.
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Re: LiFePo4 for Permobil C500S

Postby shirley_hkg » 30 Jul 2019, 11:58

100W @3.3V means 30 amp ?
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 30 Jul 2019, 12:32

Discharge (internal) 10A or 100W max whichever sooner.
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 30 Jul 2019, 17:01

I made 10 AWG with terminals instead thin alligator clips and discharging ran.
Now it's going 3 hours and 28 Ah are out.
Thanks a lot Burgerman.
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 30 Jul 2019, 17:03

Resistance matters! :clap
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 02 Aug 2019, 11:34

How can I charge a LiFePo4 176Ah cell for storage (3.300V)?
Can I use 'LiFe Charge ONE 90 to 200Ah Cell.PS8' profile and just change Charge tab -> Charge Voltage to 3.300V?
I have 3 spare cells so I want to charge them for storage.
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 02 Aug 2019, 11:40

You cant tell how much charge is in it at 3.3v.

So you must discharge a full cell by X Ah. And unless you remove exactly the same from every cell you will need to recharge each individually before assembly.

So fully charge each one. ASSEMBLE into a pack. Fully charge AS A PACK to balance correctly. Then discharge AS A PACK by say 1/3rd of its Ah for storage. So on a 176Ah pack remove approx 30% of that. Take out say 45 to 50h.
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 03 Aug 2019, 15:41

I don't have balance wires for now (I have to make them).
So can I just fully charge every cell and then discharge 30% every cell?

P.S. Can I use Revolectrix 9-wire balance cable to build 3-cell pack?
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 03 Aug 2019, 15:57

Yes if you are accurate. And watching. Or it will end up out of balance when assembled into a pack. Unless you recharge again. And yes 3S or any number from 1 to 8.
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Re: LiFePo4 for Permobil C500S

Postby Irving » 03 Aug 2019, 16:08

Yes, you can fully charge then discharge each cell individually for storage, that's what I've done with my spare Headways.

You can use the 9way balance cable to build any pack from 1S to 8S. Depending on your PL8 settings you wire it as:

Black-white1-white2-white3

Or

Black-white1-white2-Red

See pages 61-71 in the PL8 manual
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