Group Buy? Dr.Bass Steveo found 7s3p Module! Awesome Price!!

[oatnet]

It is normal for LiFe cells to plateau during both charge and discharge, they have what is known as a "flat discharge curve". As they approach capacity, yes voltage will go up; wh is a better measure of energy because it takes into account voltage and its change throught the discharge cycle. 120v is way too high for a (assuming a) 28s module, which should have a peak voltage of 102.2. If you don't catch it and you charge your cells to 120v/4.28v a cell, this will degrade their cycle life. You need to buy at $15 (or more) Digital Multimeter to work on your 2k investment, because you picked a tough pack to learn on.

Charging is a lossy process so you can expect to put in 30%+ more than the pack needs to fill up its 60ah.

======

Anyhow, regarding my own modules... My deeply discharged 7s pack completed the slow single-cell charge, consuming 2.5kw, as reported by my kill-a-watt. Its been off for a few hours and voltages are still at 3.67v/cell, so that is a really good sign, I'll let it sit for a few days and hope they hold steady.

I bulk-charged my 28s at 4.2a to 98.4v - 3.55v/cell - and it hoovered down almost 4kw hours. Most of the cells were at 3.58v, but 3 were lower. I marked them specially and put single-cell chargers on them, two came up to 3.67v really fast, the third one is still charging (finger crossed) so at best it was pretty far out of balance. In the worst case, its a lame cell that I kill on a deep discharge. I'd solder a pair of 8ga across the terminals (the buss bar supplies 2 perfect channels) of the bad cells, run 48s instead of 49s (shrug), and carry and extra 3lb of dead weight in a 196lb pack.

Anyhow, I'm also bulk-charging the remaining pair of 7s to 49.7v (3.55v/cell) to see if either of them have a low cell I should be keeping an eye on. Then I'm gonna single-cell charge them, let them sit a few days to look for self discharge, pop them into the camper-bus and take them for a test drive, and see what I can suck out of them.

They broke off a bolt in a terminal in one of my 7s. The 28s pack was warped in shipping but I fixed it. It was quickly obvious that pushing on the side of the pack would dent the cooling fins, so I gently rolled the pack to its side on a flat surface, lifted one end 6" and dropped it, same on the other end, and the pack was now straight. BTW I noticed the cooling fins on the bottom of the 28s are covered with thermal paste.

-JD

[miro13car]

zaxxon,
I charged at 2A and stil was able to bring cells to 3.6V.
It just takes so much time - more than 8 hours.
In theory 20 Ah means 2A for 10 hours.

[zaxxon]

Oatnet,

Thanks !! That’s what I hoped; a very flat curve compared to what I am use to. Now I can continue with yours and Miro13car’s input with less concern. I have experience charging our 300v 84 module Prius NiMH 13 AH pack we assembled at 4 amps. Since the 4 amps is a much higher percent charging current, and I suspect its not nearly as flat a charge curve as A123, the voltage increases steadily to the 8.4v module voltage level we charged to.

Your right I need to invest in a better meter and should lower the voltage incase I fall asleep, and or forget to check.

Your braver than me in the approach you used to square up your cells. I was thinking about using the mounting through hole with some rods and some ratchet straps to try to relieve some of the pressure before trying to ease them back into position.

[drgrieve]

Charging LiFeP04 basics.

There is a formula called CC/CV to charging these batteries. You can't pick and choose what parts of the formula is easiest - it doesn't work that way.

To charge to 100% you should charge at 3.65v at a constant current until cell or module voltage is 3.65 then decrease current holding voltage at 3.65 terminating charge when current is 0.05C (3 amps on 60h). After settling (24 - 36 hour period) the resting voltage will be 3.4V. This is 100% charged.

My main issues with some of the recent comments is as follows.

1. If you are charging at 2 amps you are below 0.05C already and you should charge to a lower voltage otherwise you are over charging.
2. Charging LiFeP04 batteries is NOT excessively lossy, you should get back 99% of the energy you put in. Counting AH is an effective way of measuring SOC if you know your starting reference.
3. A cell resting at over 3.4V is OVER charged and likely suffered a small capacity drop.

Note [except for capacity testing] I recommend charging so that the resting voltage is 3.33 or 3.34 for extended cycle life. Replace 3.65 with 3.5. Also even when testing capacity 2V is too low (not much room for error!), aim for 2.5v when capacity testing as ah between 2.5V and 2.0v is minimal.

[deVries]

Charging LiFeP04 basics.

There is a formula called CC/CV to charging these batteries. You can't pick and choose what parts of the formula is easiest - it doesn't work that way.

To charge to 100% you should charge at 3.65v at a constant current until cell or module voltage is 3.65 then decrease current holding voltage at 3.65 terminating charge when current is 0.05C (3 amps on 60h). After settling (24 - 36 hour period) the resting voltage will be 3.4V. This is 100% charged.

My main issues with some of the recent comments is as follows.

1. If you are charging at 2 amps you are below 0.05C already and you should charge to a lower voltage otherwise you are over charging.
2. Charging LiFeP04 batteries is NOT excessively lossy, you should get back 99% of the energy you put in. Counting AH is an effective way of measuring SOC if you know your starting reference.
3. A cell resting at over 3.4V is OVER charged and likely suffered a small capacity drop.

Note [except for capacity testing] I recommend charging so that the resting voltage is 3.33 or 3.34 for extended cycle life. Replace 3.65 with 3.5. Also even when testing capacity 2V is too low (not much room for error!), aim for 2.5v when capacity testing as ah between 2.5V and 2.0v is minimal.

Hi,

Since you just joined ES to literally make this 1st post, could you give us some more reference points about this information? You seem to be speaking from a position of experience and/or a good knowledge base about these cells & charging correctly.

How you done any long-term testing with these types of A123 cells?

Thanks.

[JRP3]

2. Charging LiFeP04 batteries is NOT excessively lossy, you should get back 99% of the energy you put in.

Not unless you have a charger that is 100% efficient, which you don't. 90-95% efficiency is probably normal including the charger. Losses will probably be higher if you are using resistors to do top balancing.

[zaxxon]

Charging LiFeP04 basics.

There is a formula called CC/CV to charging these batteries. You can't pick and choose what parts of the formula is easiest - it doesn't work that way.

To charge to 100% you should charge at 3.65v at a constant current until cell or module voltage is 3.65 then decrease current holding voltage at 3.65 terminating charge when current is 0.05C (3 amps on 60h). After settling (24 - 36 hour period) the resting voltage will be 3.4V. This is 100% charged.

My main issues with some of the recent comments is as follows.

1. If you are charging at 2 amps you are below 0.05C already and you should charge to a lower voltage otherwise you are over charging.
2. Charging LiFeP04 batteries is NOT excessively lossy, you should get back 99% of the energy you put in. Counting AH is an effective way of measuring SOC if you know your starting reference.
3. A cell resting at over 3.4V is OVER charged and likely suffered a small capacity drop.

Note [except for capacity testing] I recommend charging so that the resting voltage is 3.33 or 3.34 for extended cycle life. Replace 3.65 with 3.5. Also even when testing capacity 2V is too low (not much room for error!), aim for 2.5v when capacity testing as ah between 2.5V and 2.0v is minimal.

Did you mean to say or was there a typo: "To charge to 100% you should charge at 3.65v at a constant current until cell or module voltage is 3.65 then decrease current holding voltage at 3.65 ..." I am not sure your required or would want to try to drive current to a level to force the 3.65 v during the constant current portion of the charge.

Shoud this have said: To charge to 100% you should charge at constant current value greater than 0.05C and less than or equal to the max recommended by the manufacture until a maximum voltage of 3.65 is reached, and then decrease current to hold the voltage at 3.65v and terminating charge when current is 0.05C (3 amps on 60ah).

[miro13car]

I do charge to lower voltage at 2A, never reach 3.65V , usually 3.6V.
My resting volts are never higher 3.32V
Better for longevity of cell

[emiyata]

I think he is talking about battery efficiency to accept a charge. I don't think he is talking about charger efficiency.

Steve

2. Charging LiFeP04 batteries is NOT excessively lossy, you should get back 99% of the energy you put in.

Not unless you have a charger that is 100% efficient, which you don't. 90-95% efficiency is probably normal including the charger. Losses will probably be higher if you are using resistors to do top balancing.

[oatnet]

1. If you are charging at 2 amps you are below 0.05C already and you should charge to a lower voltage otherwise you are over charging.

I suppose you missed the part where I bulk charged to 3.55v/cell, and then used voltphreaks single-cell LiFePO4 chargers handle the taper charge.

2. Charging LiFeP04 batteries is NOT excessively lossy, you should get back 99% of the energy you put in. Counting AH is an effective way of measuring SOC if you know your starting reference.

I wish I had chargers that were as efficient as yours.
Amps are never a definitive measure of current, because they don't consider Volts, thats why we use watts. V x A = W

3. A cell resting at over 3.4V is OVER charged and likely suffered a small capacity drop. Note [except for capacity testing] I recommend charging so that the resting voltage is 3.33 or 3.34 for extended cycle life.

You make sweeping statements about LiFePO4 as a chemistry, that would better apply to a specific powder that you may have experience with or read about. Take the old t-sky LiFePo4 for example, which ran at a higher voltages, and would be well on its way to depleted at 3.4v. I think it was goodrum I learned the old a123 M1 test from, charge it up to 3.65v, and if it stays above 3.60v for a week it is a good cell. I expect my headways to drop to 3.37v in a few days. I have junk that sits at 3.26v. So these characteristics vary widely.

Anyhow, was the experience you are quoting from working with the a123 20ah cells in general, or these specific modules?

-JD

[SlyCayer]

Got my pack today, Lo freaking L, the packaging was non-existent and the ply box had useless wood attached to it, pictures coming later tonight....

[deVries]

Got my pack today, Lo freaking L, the packaging was non-existent and the ply box had useless wood attached to it, pictures coming later tonight....

Was there more than one module in a single crate?

So far, that seems to be a real problem, when more than 1 module is in a wood crate it overloads the wood to properly support more than one 7s3p. It will be interesting to see if they will change their method of crating the modules, and, perhaps, one 7s3p module per crate is best. Crating one module per crate will prevent the modules from damaging each other & "overloading" the crate, hopefully, preventing it from bowing & distorting the wood stressing the modules & cells out of alignment.

[SlyCayer]

Here is the packaging part, sorry for quality... Iphone 4s ain't the best.

[SlyCayer]

Was there more than one module in a single crate?

Yes, only 1, but it looks good tho, the packaging is just none-existent.

[deVries]

Was there more than one module in a single crate?

Yes, only 1, but it looks good tho, the packaging is just none-existent.

That one picture is very strange with all the layers of wood? What was the purpose of all the layers of wood?

What's with all those layers of wood? :D

It does look that ordering One Module per One Crate will get the best results for safe shipping.

[njloof]

That one picture is very strange with all the layers of wood? What was the purpose of all the layers of wood?

If I recall, they used those as shims to keep the battery from sliding around inside the box (for whatever that's worth).

[totinen]

That one picture is very strange with all the layers of wood? What was the purpose of all the layers of wood?

Maybe it prevents battery from bending?

[liveforphysics]

Charging LiFeP04 basics.

There is a formula called CC/CV to charging these batteries. You can't pick and choose what parts of the formula is easiest - it doesn't work that way.

To charge to 100% you should charge at 3.65v at a constant current until cell or module voltage is 3.65 then decrease current holding voltage at 3.65 terminating charge when current is 0.05C (3 amps on 60h). After settling (24 - 36 hour period) the resting voltage will be 3.4V. This is 100% charged.

My main issues with some of the recent comments is as follows.

1. If you are charging at 2 amps you are below 0.05C already and you should charge to a lower voltage otherwise you are over charging.
2. Charging LiFeP04 batteries is NOT excessively lossy, you should get back 99% of the energy you put in. Counting AH is an effective way of measuring SOC if you know your starting reference.
3. A cell resting at over 3.4V is OVER charged and likely suffered a small capacity drop.

Note [except for capacity testing] I recommend charging so that the resting voltage is 3.33 or 3.34 for extended cycle life. Replace 3.65 with 3.5. Also even when testing capacity 2V is too low (not much room for error!), aim for 2.5v when capacity testing as ah between 2.5V and 2.0v is minimal.

This is a noob that's used to dealing with high parasitic loss LiFePO4. ThunderSags, ping, deadways, etc.

Set a current limited supply to 3.65v/cell and forget about it. You don't have to turn current down, it's a natural effect of cell voltage being close to the power supply max voltage (current can only flow when you have a voltage imbalance across a resistance to make it flow). You can't overcharge LiFePO4 at 3.65v, and cells that have good solvents won't have any dissociation effects being left at 3.65v over time (unlike other blends being left at 4.3v etc). Good LiFePO4 (like A123) will stay at 3.65v for months resting.

[texaspyro]

A123 recommends float charging their cells a 3.4V (actually they say charge them to 3.6V then float them at 3.4V). My testing shows about zero capacity difference between 3.4 and 3.6V, you just get to the fully charged state a lot quicker a 3.6V

[Ypedal]

That one picture is very strange with all the layers of wood? What was the purpose of all the layers of wood?

If I recall, they used those as shims to keep the battery from sliding around inside the box (for whatever that's worth).

a wood box is better than a cardboard box ...

[deVries]

a wood box is better than a cardboard box ...

Agreed. I don't think it would be possible to use cardboard for these heavy modules. No way.

I am just observing & referencing that one pic that I put in my original post... check it out... all the layers of wood on one side... anyway, these were probably just spacers or "shims" instead of using Styrofoam or air bubble spacers, but it is a confusing pic to me, especially, when compared to another photo that shows the module fit very tightly within the crate... and, you don't see all that spacer/shims layers of wood or how those could even fit within that tight-fitting crate. I don't see how those layers could even be used in that other photo that SlyCayer posted. You have to compare those two photos to understand what I'm getting at...

After looking at that photo again I see SlyCayer wrote: "the ply box had useless wood attached to it"

It seems this many layers of wood might also have been used for the outside bottom of the crate underneath the module to give some crazy support to the bottom/floor of the module.

[davec]

so we're upto post # 23 here
lots of battery pics and chatter
yet no one bothered to test their pack and post results?
isn;t anyone a bit curious if their 7s3p can put out at least 54aH ?
i mean when doc bass did his thread- it was one of the first things he did.

[chessir]

I would have already tested it if the modules were 8s3p not 7s.

[kevo]

not post #23, but page 23 of course!

[deVries]

It's now Wednesday almost noon in OZ.

I expect Sutho will be reporting soon about his 22 modules of 7s3p sometime later today, hopefully!

Sutho, we look forward to your initial report w/many details to follow too, hopefully!