What's the BEST battery for eBike?

[Just]

I don't buy battery cells without seeing their spec :-)

[GM Canada]

True the discussion is about cells, but the title is "Battery". Most people dropping in here would not be building their own battery. Most people would just be looking for a reliable battery. But I guess that's beside the point.

So what info on the GM cells would you need?

Gary

[Just]

So what info on the GM cells would you need?

1) Technology
2) Internal Resistance
3) max allowed charge current
4) max allowed continuous discharge current
5) max allowed peak discharge current
6) # of life cycles
7) Operation Range (Voltages) - actually depends on technology
....

[GM Canada]

1) Technology
2) Internal Resistance
3) max allowed charge current
4) max allowed continuous discharge current
5) max allowed peak discharge current
6) # of life cycles
7) Operation Range (Voltages) - actually depends on technology
....

Really I'm the least technical person to attempt these answers, but lets start with this.



That should cover questions 3 to 6.

1 - I don't even understand the question
2 - Can I just measure this with my meter?
7 - fully charged 48v pack 58.4 low cutoff I don't know. But I guess you are looking for min/max per cell?

4 out of 7 with only 1 minute of research, not a bad start..

Now you tell me, are any of these numbers any good? They look to me to be OK for the average consumer. But as I said. I know nothing!

Gary

[Lollandster]

1 - I don't even understand the question
2 - Can I just measure this with my meter?
7 - fully charged 48v pack 58.4 low cutoff I don't know. But I guess you are looking for min/max per cell?

1. I think the answer to number 1 is LiFePO4

2. You can use the Cycle Analyst to measure the internal resistance. The cycle analyst 3 has a screen (I think it is two steps to the left) that shows a value with a omega sign behind it. As far as I can understand this is the internal resistance of the battery calculated from voltage drop over current draw. I haven't gotten this confirmed though as the documentation for the CA3 is very limited at the moment. The value is very close to my own calculation of internal resistance so I think that is what it is.
If you don't have the CA3 connected to one of your bikes you can use the old one, but unless I am mistaken you have to do the calculation manually.

7. As he said this is dependent on the technology so you only need the cell count and technology to figure this out. But listing the LVC and HVC of the BMS is always reassuring if only to see that things are as expected.

[Just]

I need to know an internal resistance of the cells - it's very important parameter. Some of the LiFePo4 cells on the market have an internal resistance of 100mOhm - not acceptable at all! As for me, I see a warning/stop sign when a manufacturer doesn't include an internal resistance parameter in his cells spec.

[Lollandster]

Note that when you use the CA to measure the internal resistance you measure the whole pack and not a single cell.

My very cheap battery pack from BMSBattery.com has 150mohm internal resistance, but it has 12 cells connected in serial giving it about 12,5mohm of internal resistance per cell. The much better Headway battery from the same place has about 3mohm per cell. My battery is rated 1C while the headway is rated 10C. This means that the Headway will have a higher voltage drop than my cheap battery if both where driven at their respectable max.

No LiFePO4 battery compatible with the MagicPie will have close to 100mohm per cell as that would give you a voltage drop of 2.5v per cell at 25amps giving you a total pack voltage of 12.8v for a 16 cell battery and that would trigger the LVC and shut down the bike.

[Just]

Headway will have a higher voltage drop than my cheap battery

No, vice versa. Since the Headway cells have less internal resistance, a voltage drop over these cells will be less

[Lollandster]

Headway will have a higher voltage drop than my cheap battery

No, vice versa. Since the Headway cells have less internal resistance, a voltage drop over these cells will be less

No, what I said is correct, you probably read it wrong

Max for My cheap cell is 10Amps max (10Ah 1C) with 12.5mohm internal resistance: 10Ah*0.0125ohm=0.125v drop
Headway cell is 100Amps max (10Ah 10C) with 3mohm internal resistance: 100Ah*0.003ohm=0.3v drop

If both where driven at the same amount amps and not their respectable max you would be right.

[Just]

"If both where driven at the same amount amps..." - this is the way to compare the cells ...

[Lollandster]

"If both where driven at the same amount amps..." - this is the way to compare the cells ...

The two different cells are meant for two very different applications. The Headway cells can do 100amps while the cheap cells can only do 10amps. At 10 amps both have an acceptable voltage drop (0.125v and 0.030v) so to see any real benefit from buying the more expensive Headway cell you need to move up to a amp draws that the cheap cells can't do, so you wouldn't be comparing them in the first place.

Since this is a thread about finding the best battery and not just a suitable battery then looking at the internal resistance is probably the safest thing, but you also need to compare that to the capacity of the battery. If you have a 5Ah battery and a 10Ah battery with the same internal resistance then the 5Ah battery will be twice as good because you will half the internal resistance when you parallel connect two of them to make a 10Ah battery. I think this is one of the reason why you never see the internal resistance in the feature list of batteries, it just gets too complicated to compare.
Even the C rating is too complicated for many.

For normal buyers: If the C rating on the battery is high enough for your application, then chances are that the voltage drop will be low enough.

[GM Canada]

1. I think the answer to number 1 is LiFePO4

I thought that might of been the answer, but it seemed I was being asked the technology of a lifepo4 battery.

2. You can use the Cycle Analyst to measure the internal resistance. The cycle analyst 3 has a screen (I think it is two steps to the left) that shows a value with a omega sign behind it. As far as I can understand this is the internal resistance of the battery calculated from voltage drop over current draw. I haven't gotten this confirmed though as the documentation for the CA3 is very limited at the moment. The value is very close to my own calculation of internal resistance so I think that is what it is.
If you don't have the CA3 connected to one of your bikes you can use the old one, but unless I am mistaken you have to do the calculation manually.

Winter is here now and I don't think I will be riding for a while. I have actually been stripping parts off of three of my bikes and selling them. Changes and upgrades are coming. Is your calculation of the internal resistance in this thread? I must have missed it. I'll ask GM China this question, maybe they will respond.

7. As he said this is dependent on the technology so you only need the cell count and technology to figure this out. But listing the LVC and HVC of the BMS is always reassuring if only to see that things are as expected.

Now I'm getting confused again. Are we looking for the high/low values of the battery or the individual cell?

So it seems we are a 5 out of 7 answered?

Gary

[Lollandster]

7. As he said this is dependent on the technology so you only need the cell count and technology to figure this out. But listing the LVC and HVC of the BMS is always reassuring if only to see that things are as expected.

Now I'm getting confused again. Are we looking for the high/low values of the battery or the individual cell?

I was guessing the whole pack, but this is not a value I would be looking for since it is dependent on the technology used and very easy to find out. The full "off the charger" voltage is useful so you don't go and buy a 36v battery and a 24v battery thinking that serial connecting them and powering your MagicPie with it is OK because it is only 60v total.

Winter is here now and I don't think I will be riding for a while. I have actually been stripping parts off of three of my bikes and selling them. Changes and upgrades are coming. Is your calculation of the internal resistance in this thread? I must have missed it. I'll ask GM China this question, maybe they will respond.

But riding in the snow is so much fun I will try driving on the lake when I get my new battery.

My calculation was not in the thread no, I forgot exactly how I did it and didn't want to tell the wrong procedure.
Instead of thinking I will quote Justin from Grin tech:

Just be sure to input your battery internal resistance by looking at your pack voltage before and after applying full throttle, then use RBatt = (V1 - V2) / A, where V1 is the voltage with no throttle, V2 is the voltage at full throttle, and A is the current limit of the controller.

If you have the CA it is easier to use VMin from the CA as V2 and AMax as A. Using the controller limit as A sounds unreliable to me.
This will give you the total resistance of the battery and not the cells. If you have a single cell you can do this with a load and a multimeter.

[Morgen 3Eman]

Hi Just,

Since you seem to be saying "Nay" to everything put forth, have you already decided what you are going to do? Leaning toward something?

TTFN,
Dennis

[GM Canada]

After a 10 k power ride with one battery and two pies I have some statistics to toy with. The test battery is a 48v10ah LiFePO4 aluminum cased GM battery with about 400-500 cycles run through it by now. The battery is configured in the CA3 as a 16 cell 10 Amp LiFe battery. The number beside the ohm symbol on the CA3 is .179. If I understand correctly this number gets divided by the number of cells in the battery to determine the individual cell internal resistance. So .179/16 = .011.

The voltage of the battery is 53.4 volts at rest. with several hard dual MP III full torque take offs and 10 k of hard riding vmin droped to 39.9 volts. and Amax went to 56. SO now we have
((volts at rest - Vmin)/Amax)/number of cells)

 ((53.4 - 39.9)/56)/16) = .015

So I could be mistaken but those numbers seem pretty good to me. Of course I could be calculating this all wrong as well. What do I know 

And yes I realize a 56 amp draw on my 48v10ah battery is not good but I could not figure out how to set the CA for 48v30ah and run all three in parallel. It seems when I do 30 amps 48 cells it thinks my battery is a 153.3 volts of something like that. So I just did this test with one.

Maybe I need to ask Justin that one.

Gary