Better Balancing

wifi442

wifi442

100 µW
Joined
Jan 10, 2012
Messages
7
I am having issues getting balanced correctly. I bulk charge with a BMS 600w charger for my 12c setup. The charger is great and fast. The problem is balancing. I use the battery medic on each bank to do the balancing. By accident I ended up with 3 Battery Medics. Every one of them shows a different reading on any given pack which is making me very nervous. They are horribly out of adjustment and don't know which one of them to believe. It almost seems like the are un-balancing my pack!

Is there a better option for me? I was thinking the iCharger but can it just perform balancing or does it need the charge leads connected as well? I'd rather not have to split the pack apart just to balance charge. Is there another option like the battery medic that is more accurate?

Thanks
 
You could use a volt meter to read the balance taps to get an accurate reading to determine which battery medic is the most accurate.
 
Battery medics are known to not be accurate, so your results are not surprising at all. They are fantastic disbalancers, lol.

Do you have a 12S pack?
If so, you could pick up an iCharger 106B+ and only use it for balancing.
Yes, you have to plug in the charge leads, but i have an idea..

Basically take your lipos and put them in parallel ( also using a parallel balance harness of course ), then hook them up to series. for bulk charging.

When you need to balance, simply break apart the series connection and charge the two big parallel packs separately.
If you have good, tested packs with no dud cells, you will not need to balance for a hundred cycles or more anyway.

Another idea is to get the hyperion 12S charger and use that. Not as precise as the iCharger, not as many functions, but it would be 5x better than your battery medic still.

wifi442 said:
I am having issues getting balanced correctly. I bulk charge with a BMS 600w charger for my 12c setup. The charger is great and fast. The problem is balancing. I use the battery medic on each bank to do the balancing. By accident I ended up with 3 Battery Medics. Every one of them shows a different reading on any given pack which is making me very nervous. They are horribly out of adjustment and don't know which one of them to believe. It almost seems like the are un-balancing my pack!

Is there a better option for me? I was thinking the iCharger but can it just perform balancing or does it need the charge leads connected as well? I'd rather not have to split the pack apart just to balance charge. Is there another option like the battery medic that is more accurate?

Thanks
Click to expand...
 
neptronix said:
Battery medics are known to not be accurate, so your results are not surprising at all. They are fantastic disbalancers, lol.

Do you have a 12S pack?
If so, you could pick up an iCharger 106B+ and only use it for balancing.
Yes, you have to plug in the charge leads, but i have an idea..

Basically take your lipos and put them in parallel ( also using a parallel balance harness of course ), then hook them up to series. for bulk charging.

When you need to balance, simply break apart the series connection and charge the two big parallel packs separately.
If you have good, tested packs with no dud cells, you will not need to balance for a hundred cycles or more anyway.

Another idea is to get the hyperion 12S charger and use that. Not as precise as the iCharger, not as many functions, but it would be 5x better than your battery medic still.
Click to expand...

Yes 12S Pack. I actually used to charge like that. I have everything paralleled balance leads etc. Then I would break the series apart and charge each side separately. I was using a Turnigy 4x 6s charger before. I guess I should have not sold it so soon!

The Hyperion charger sounds interesting. So it will charge the two packs even though they are still in series?
 
captain387 said:
You could use a volt meter to read the balance taps to get an accurate reading to determine which battery medic is the most accurate.
Click to expand...

Yes, I checked with a volt meter to verify my packs are ok. One of the BM is fairly close. But to balance both sides separately with only 1 BM is rather tedious. But for now this is how it's gonna be done :)
 
I like that charger. Looks pretty good actually. Looks like I can just plug everything into it without changing my setup and it would balance charge the whole bike in series at once. I would just need to hack up another PC power supply LOL

Thanks for the great info!
 
No prob.. yeah; now you just need a monster size power supply. maybe there are some surplus 24v 700-900w server power supplies out there?

I don't know much about using computer PSUs, other than they are overrated and running them at their advertised spec = magic smoke show.

You really need 24v to take advantage of the juice this sucker can pump out.
 
I know the medics are a cheap solution but I for one have had great success with mine, I have over 3000 miles stacked up on my bike now and I have yet to have any trouble with mine
.. I also used it on my previous build for a couple thousand before that. I have also seen many others use them with success, I understand they are not the most accurate thing available but if you keep LiPo balanced within a couple hundredths of a volt it functions perfectly. I think a little looking into these balancers before getting a new setup is in order. I would like to compare mine to yours 442, to see how they stack up..
 
Plenty depends on what you call balanced. If you are practicing moderate DOD, you can stop worring about .05v.

I begin to take notice when a pack gets a cell .1 off. I don't spend a ton of time worring about the balance of my packs. When it gets to where I have a cell always off balance, that pack gets chucked in the experiment later pile.
 
I agree, a few points off is fine, I have him setup with a cutoff voltage of 49.9 so it has plenty of room on the top and a LVC of 40v. So, he's really pretty safe...
 
dogman said:
Plenty depends on what you call balanced. If you are practicing moderate DOD, you can stop worring about .05v.

I begin to take notice when a pack gets a cell .1 off. I don't spend a ton of time worring about the balance of my packs. When it gets to where I have a cell always off balance, that pack gets chucked in the experiment later pile.
Click to expand...

Depending on where you are in the charge, 0.05v can be 5% of your total capacity.
And it does matter if you don't view lipos as disposable and want to get 300-600+ cycles out of them.

NASA did a study a while back, that proved that charging lithium ions to a various voltage affected their cell life pretty dramatically. At 4.2v/cell, they were getting whatever the rated cycles were. At 4.15v/cell, they had almost doubled it. At all the way down to 3.9v/cell, they were getting about 6-8 times the cycle life out of the same pack.

Cutting the DOD out at the bottom did not improve the life if the cells.

So here's where my advice for 300-600+ cycles comes in. If 0.05v is the difference between even 50% more life, why would you want your cells significantly unbalanced all the time? some cells would die ( according to whatever pattern your charging device disbalances them ) far sooner than the others. You'd end up with a ton of RC lipo bricks with some dead cells, some healthy down the line. So you trash bin those, or cut them all up and have yourself a grand time salvaging what's left, all because you didn't bother to spend some more $ on charging equipment.

Lithium batteries need to stay fairly well balanced for just that reason. If you care to spend the time reading, there are dozens of research papers on this topic.
 
That's interesting right there, I don't claim to know it all, and I have to say, logically thinking it makes sense. One question is then since the LVC of the charge did not harm them, is it safe to say you can run LiPo down to 3v per cell and not harm them? Assuming they are not below that...
 
http://endless-sphere.com/forums/viewtopic.php?f=14&t=31313&start=30

Methods is going to be doing some testing of the balancers and test them for accuracy. Will perhaps help with the accuracy issue you are having if Methods comes up with a easy fix.
 
From what ive read, taking packs to 0%SOC will harm their life, but I've no personal experience. Really, given that you may only get about 2-5% of your pack by going from ~3.6 to 3.0 there doesnt seem much point in risking it.

Personally, I dont worry so long as the delta V of my packs is less than about 25mv at the end of the charge, about 4.15v.
 
All very good information. As an update I bit the bullet and got the Hyperion EOS1420I NET3. So far it seems like a very nice charger. Plugged right in and charged at 12S. Updated the FW to latest version. First balance got everything within 3 thousandths of a volt! Of course that is only as accurate as the charger itself. The two Multimeters I have only measure to hundredths but they are spot on. In any case it is 100% better than the bad luck I had with the Medics.

Not to change the subject too much here but how is this for a power supply? Looks like a great match for the Hyperion. Good Price?

http://www.ebay.com/itm/270867517540?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
 
dogman said:
Plenty depends on what you call balanced. If you are practicing moderate DOD, you can stop worring about .05v.

I begin to take notice when a pack gets a cell .1 off. I don't spend a ton of time worring about the balance of my packs. When it gets to where I have a cell always off balance, that pack gets chucked in the experiment later pile.
Click to expand...

Yes yes yes

Don't be too anal about it.

Just pay attention...
 
I charge and balance a 72Ah 13S lithium pack, and have done lots of algo help, and been the cause of quite a few firmware updates on the hyperions. Including the corrected PB charge algo, 36 and 48 volt addition, and much other stuff including the capacity increase from 50Ah to 100 Ah for lithiums. And up to 200 for PB.

I also know a lot about batteries. The hyperion charges and controls the charge to allow the 300mA balancer to keep the cells from going too high, during charge. This is what damages a lot of cells. And why you should use a system that prevents this, rather than a simple charge and seperate balancer. It also leaves all cells within a couple of thousandths of a volt at the top. Verified with my certified digital voltmeter.

Of course if you rebalance at a different state of charge, it can be completely different and take hours. And then have to be reversed again when charged. So only balance at the top during charge. Not every cell is the same voltage or has the exact same discharge curve. So balance based on voltage changes with state of charge. This will screw up most attempts to balance a pack...

But you will not be disapointed, see here:
http://www.wheelchairdriver.com/BM-MK3-lithium-charging-powerchair.htm
 
You must log in or register to reply here.

Similar threads

M
Batt not charging - help!! (52V 14S 4P - JBD BMS - 14S 50A UART BT / JBD-SP14S004)
Replies
14
Views
1,802
m0rg5
M
O
Repaired my Grin pack, I think...
Replies
8
Views
1,426
999zip999
999zip999
B
Parallel Charging into three different batteries with separate BMS's
Replies
10
Views
1,964
999zip999
999zip999
Z
Potentially Stupid Idea for an NiMh to LiFePO4/Na+ Retrofit on a Hybrid
Replies
10
Views
977
ZFreaky
Z
J
LIPO charging
2
Replies
29
Views
3,630
DingusMcGee
D
Back
Top