Battery Medic balancers for headway cells?

[johnnyz]

Has anyone have experience with these units. I have 28 headway cells 15 ah each connect serially but no BMS. I was bulk charging but having to keep an eye on top cell voltage and cutting the charge off at that point. I used some individual modules that attached to each cell and began shunting voltage at 3.5 volts but only 450 mah, it wasnt enough and some failed so useless. These can monitor and balance 6 cells at a time so if I had 5 units and initiated a balance situation, would they be able to balance the cells relatively well before charging?....most of the time cell voltages are within 0.05 volts.

Thanks

John

 

[Ykick]

Don’t waste your money going down this path. BM6’s may seem like a good idea but they’re not very robust for balancing large capacity cells. One for occasional tinkering is fine but it’s not a viable system to invest in for regular daily use.

Plus, LiFe chemistry isn’t nearly as linear with regard to voltage/SOC as Lipoly which these devices are primarily used with.

You’d do yourself more benefit installing a decent BMS or 2 or 3 in series if need be.

 

[johnnyz]

Don’t waste your money going down this path. BM6’s may seem like a good idea but they’re not very robust for balancing large capacity cells. One for occasional tinkering is fine but it’s not a viable system to invest in for regular daily use.

Plus, LiFe chemistry isn’t nearly as linear with regard to voltage/SOC as Lipoly which these devices are primarily used with.

You’d do yourself more benefit installing a decent BMS or 2 or 3 in series if need be.

I guess that is the question...finding a decent BMS even putting more than one in series that wont choke on 65 amps or fail taking one or more of my cells with it...and at a decent price

John

 

[Ykick]

28S from this page might do it but there’s 2 MOQ (minimum order quantity) - http://bestechpower.com/27Sto32Spcmbmspcbforlifepo4batterypack/

You might be better off financially buying 2qty 14S, 80A or more from this page and run them in series - http://bestechpower.com/448v14spcmbmspcbforlifepo4batterypack/

I believe series operation is simple and very doable although I’ve never personally done it yet?

With regard to reliability of not KILLING cells I don’t like any of these balance circuits. I’ve suffered several shorted balance transistors on various BMS and I sleep better simply desoldering/lifting the balance drain resistors. I then balance manually every once in a while with a 1S charge through balance leads, if needed. Rarely needs balancing for my Lipoly packs.

On the other hand, active OVP/UVP (over voltage protection/under voltage protection) has definitely saved numerous cells to date.

It’s saved more cells than the shorted balance transistors have killed. None actually, since I noticed the slight drain early on then dug down and eliminated the problem(s).

Is your 65A absolute max from personal measurement? Sustained for any period of time?

 

[johnnyz]

Thanks for the reply
I think that a good bottom balancing is what is next...this way even though im sacrificing energy at the top, they should all discharge the same...this way with the cycle satiator, I can set the charge at something like 80% of the charge...keeping an eye on what cell gets there first,but we will see...i suspect that they will be fairly close.

John

 

[Ykick]

Bottom balancing, really? Your cells and good luck…

 

[wesnewell]

I've been using a couple of those for a few years. They suck for balancing, but they work pretty good as voltage limiters on the high end of the charge as long as your charger has ramped down the charge current. Just set it to 3.6V for headway cells.

 

[johnnyz]

I've been using a couple of those for a few years. They suck for balancing, but they work pretty good as voltage limiters on the high end of the charge as long as your charger has ramped down the charge current. Just set it to 3.6V for headway cells.

Thanks for the info...well I think that the Satiator will do this and you can program it to charge at whatever voltage you like..so that I can set it to charge at 3.5 volts x 14 (half the pack)=49 volts instead of 51.1..and this way as the current continually drops it will give the Battery Medics time to shunt some cells that are getting there faster than the others and allow the others time to catch up.

John

 

[johnnyz]

Just a quick update

Yes indeed, the Battery medics work fine with my headway cells, balancing them at the TOP of the charge...that is I set the discharge on the battery medics at 3.5 volts, and so, when any of the cells get at 3.5 volts the battery medic begins discharging the cell and this allows the others to catch up. Mind you I have a Cycle Satiator and I set the voltage cut off at the point where the one cell that has the least amount of capacity and reaches 3.6 volts. At this point most of the cells are at 3.5 volts which really is 95% charged and some of the highest capacity cells are at 3.45. I get about 13 amp hours out of this 15 amp hour pack and considering Headway cells are all over the map consistency wise, this works and works well.

John

 

[motomech]

The new black Battery Medics are junk and don't offer the versatility and performance of the older blue one's.
Turnigy has a new checker/balancer that is getting good reviews;
http://www.hobbyking.com/hobbyking/store/__26136__Turnigy_DLUX_LIPO_Battery_Cell_Display_and_Balancer_2S_6S_.html
I would like to try one out, but I have enough of the blues ones so I'm happy.

 

[Ykick]

The new black Battery Medics are junk and don't offer the versatility and performance of the older blue one's.
Turnigy has a new checker/balancer that is getting good reviews;
http://www.hobbyking.com/hobbyking/store/__26136__Turnigy_DLUX_LIPO_Battery_Cell_Display_and_Balancer_2S_6S_.html
I would like to try one out, but I have enough of the blues ones so I'm happy.

Balancing Current: 50mA

That's cute...

 

[999zip999]

How are you using your cells what amp is your controller maybe you're using your cells at too high of a c-rate. Headway are over rated and at high discharge hard to keep in balance.

 

[johnnyz]

How are you using your cells what amp is your controller maybe you're using your cells at too high of a c-rate. Headway are over rated and at high discharge hard to keep in balance.

Not true if done properly...and yes headways are the worst cells ive ever seen for consistency..however after 23 kms and using over 9 ah's....look at the voltages...pretty dang close...yes they get worse only at the end of the charge and only 2 which have less capacity then the others.
View attachment 1


I will post later tonight when I charge them up to show how close I get them...

I use the Cycle Satiator...set it to 42.1 volts and 6.5 amps and then cycles down the amps at 42.1 and the medics are able to keep the top ones (or the lowest in capacity) in check. ( I have a 72 volt pack and simply use 2 charging leads charging as though there are 2 36 volt batteries as the Satiator cant charge 72 volts)

Yes I agree that Headways are over rated. There is NO WAY these are a 10 c battery...more like a 2c continuous with 4c burst. My pack fully charged is 80 volts ...full throttle pulling 55 amps and they sag to 68.5 volts. Thats a lot of sag!!

John

 

[johnnyz]

The new black Battery Medics are junk and don't offer the versatility and performance of the older blue one's.
Turnigy has a new checker/balancer that is getting good reviews;
http://www.hobbyking.com/hobbyking/store/__26136__Turnigy_DLUX_LIPO_Battery_Cell_Display_and_Balancer_2S_6S_.html
I would like to try one out, but I have enough of the blues ones so I'm happy.

If this doesnt have a discharging function then it WONT work in the way I am using the battery medics. And the ones shown are ones I ordered and the voltages are very close when checked with my voltmeter. I disagree, I think they are really quite good.

 

[johnnyz]

The new black Battery Medics are junk and don't offer the versatility and performance of the older blue one's.
Turnigy has a new checker/balancer that is getting good reviews;
http://www.hobbyking.com/hobbyking/store/__26136__Turnigy_DLUX_LIPO_Battery_Cell_Display_and_Balancer_2S_6S_.html
I would like to try one out, but I have enough of the blues ones so I'm happy.

Balancing Current: 50mA

That's cute...

Thats 200-450 mah resistor discharge rate which is better than almost all chinese BMS units.


John

 

[Ykick]

The new black Battery Medics are junk and don't offer the versatility and performance of the older blue one's.
Turnigy has a new checker/balancer that is getting good reviews;
http://www.hobbyking.com/hobbyking/store/__26136__Turnigy_DLUX_LIPO_Battery_Cell_Display_and_Balancer_2S_6S_.html
I would like to try one out, but I have enough of the blues ones so I'm happy.

Balancing Current: 50mA

That's cute...

Thats 200-450 mah resistor discharge rate which is better than almost all chinese BMS units.


John

Where do you get that value from? I simply copy & pasted the Balancing Current specification.

Most Chinese BMS discharge around 80mA and "hours" have nothing to do with the current dropped across the bleed resistors.

 

[johnnyz]

Good grief...how much testing have you done with these units????


Spec.
Size: 93.5 x 60 x 17mm
Battery types: Li-polymer (2 ~ 6 cell)
Cell voltage range: 2.0v ~ 3.9v
Discharge: 3.0v ~ 4.2v
Bleed Current: 200~450mA

 

[Ykick]

No good or bad grief about it.

I was referring to this one posted by motomech - http://www.hobbyking.com/hobbyking/store/__26136__Turnigy_DLUX_LIPO_Battery_Cell_Display_and_Balancer_2S_6S_.html

I've heavily used the one in your OP and it's a POS, IMO. But to each their own...

 

[nutnspecial]

I've been using one for a year and I think if they get too hot on discharge stuff fries. The function buttons don't work right but they still are a good 'checker'. Prob why the turnigy ones got rid of discharge function and do a lighter balance current?
I'd be willing to bet the turnigy will hold up better but think the discharge function is better suited to my use.

Anyway, when found right now the actual HK medics cost like +20$, while there are these unbranded ones available for a fair price of 10$. Thinking they'll do the trick just fine if kept cool during any bleeding off of high cells.
http://www.ebay.com/itm/RC-2s-6s-Lipo-Li-Fe-Battery-Balancer-LCD-Voltage-Meter-Tester-Discharg-er-E1I5-/252344508568?hash=item3ac0e7a098:g:xHMAAOSwiylXA2g8
http://www.ebay.com/itm/3-in-1-LCD-Discharger-Balancer-Meter-Tester-for-2-6S-lipo-Li-Fe-battery-H5-/111774405213?hash=item1a0646125d:g:T2UAAOSw37tV-ryl
Hmm, the one direct from hong kong for 2$ (15%) less?

 

[wineboyrider]

Does anyone use incandescent bulbs to pull down the high voltage cells? I have had such good luck with keeping my new multistars balanced as the only thing I have to do with them is put each 4s pack on a cheap ass turnigy balance charger I bought years ago.

 

[johnnyz]

No good or bad grief about it.

I was referring to this one posted by motomech - http://www.hobbyking.com/hobbyking/store/__26136__Turnigy_DLUX_LIPO_Battery_Cell_Display_and_Balancer_2S_6S_.html

I've heavily used the one in your OP and it's a POS, IMO. But to each their own...

lol...but THAT one is NOT a battery medic!...good grief

John

 

[johnnyz]

Ok...here are the cells at 42.1 volts (12 cells) and 4 amps and dropping...remember I have the charger start to decrease the amperage as soon as the total voltage reaches 42.1. You can see the first cell get to 3.5 volts and the battery medic is starting to work to bleed off the charge coming into the cell.

This is the LEAST capacity cell.

Then because the amperage is dropping the Battery medic with 400+ma is able to effectively thwart the cell from going any higher allowing the others to "catch up"View attachment 2

It reaches 3.6 volts and stops there as the amperage begins winding down. It actually goes down from there..most of the cells eventually get to 3.5 + volts which is almost fully charged..the others at 3.4+ volts are left as they are as they are NOT the cells that get empty first but the cells that get to 3.5 volts first are.

The last picture is the voltage at 42.1 but only .9 amps.

Even though I am not utilizing the total amount of energy from all the cells as a pack, I can still get about 13 amps from this pack. Even if you were to completely get every cell to 3.65 volts, the less capacity cells would hit 3 volts first and from there there's not much left in the cell and you would have to stop the discharge anyway. The Headway cells are just not close enough in consistency to have them balance up much better than this, at least not the cells I have been using through the years.

 

[whereswally606]

from what you are doing here, this looks like top balancing, not bottom balancing. You are just using battery medics to prevent overcharge of your weakest cell. Think of this though, you can only discharge the amount that the weakest cell holds. When bulk charging all cells are taking a more or less equal share of the energy. That means there is little point in bleeding that cell that reaches the voltage first as its getting full (lifepo4 I'm talking here). If bottom balancing is done properly down to say 3v or absolute lowest about 2.75v (look at the battery spec for your brand) then the charge from the bottom should terminate when the first cell goes above your termination voltage 3.65v or so any extra you put in you can use when discharging as that weak (least capacity cell) will empty first too.

I would say use them to prevent overcharge but don't wait for the rest of the cells to catch up. That weakest cell is bleeding first and bleeding longest and its always gonna be first as you are making it work hardest so you are killing the weakest member with the medic. bobc is making a good bottom balancing solution for lifepo4 which you use once or twice a year and then just be careful about how much energy you put in and take out.

Hope i've made some sense here. I am only speaking about lifepo4 not anything else.

 

[johnnyz]

from what you are doing here, this looks like top balancing, not bottom balancing. You are just using battery medics to prevent overcharge of your weakest cell. Think of this though, you can only discharge the amount that the weakest cell holds. When bulk charging all cells are taking a more or less equal share of the energy. That means there is little point in bleeding that cell that reaches the voltage first as its getting full (lifepo4 I'm talking here). If bottom balancing is done properly down to say 3v or absolute lowest about 2.75v (look at the battery spec for your brand) then the charge from the bottom should terminate when the first cell goes above your termination voltage 3.65v or so any extra you put in you can use when discharging as that weak (least capacity cell) will empty first too.

I would say use them to prevent overcharge but don't wait for the rest of the cells to catch up. That weakest cell is bleeding first and bleeding longest and its always gonna be first as you are making it work hardest so you are killing the weakest member with the medic. bobc is making a good bottom balancing solution for lifepo4 which you use once or twice a year and then just be careful about how much energy you put in and take out.

Hope i've made some sense here. I am only speaking about lifepo4 not anything else.

Hi there and thanks for the post.

I disagree that I am killing the weakest cell because I am bleeding the energy from it. If we were to follow that logic would it not hold that any bleeding type BMS also kills cells?. I am not overcharging the cell in fact charging it with slightly less than it needs

I tried bottom balancing and only used the battery medics for reference. guess what?...over time and I do mean very little time, the cell voltages started to vary..the first cell that got to 3.6 volts, I then adjusted the cycle satiator to charge at that voltage. The next 4 or 5 times I discharged and charged they remained relatively consistent. Then they started to diverge...a little bit at first but greater the more of a discharge I took out of them. I then had to LOWER the total amount of voltage from the CS so that the very top cell would go over, and then had to lower it some more..then others began to diverge...finally I decided to bottom balance again (a 2 day affair) and viola, it happened again...this time I had enough and I began bleeding the top or weakest cell with the battery medics and the more I did this the more the cells got into balance at the top...also, I noticed that I didnt have as much power (couldnt pull as many watts) with bottom balancing as top balancing. I know when the weakest cell is starting to give out as the voltage cant bounce back as quickly and under load it sags to 64volts...that not being a state of charge for the whole pack but from the 2 weakest cells.

These cells are terrible in their capacity differences and because of this it is illogical to think that bottom balancing would work. Invariably they begin to diverge over time..so with these anyway, bottom balancing DOES NOT work

John