A different approach to battery management...

[methods]

Someone needs to measure the current at each cell to see how they are tapping the pack. Have you taken that measurement yet or reverse engineered the circuit?

Even a few mA is enough to trash a pack in no time flat - even if it does not drain a subset of cells down to the damage point it will create the worst possible balancing situation where only one cell is down and the balancer has to bring all the rest down to meet it - or worse yet if the user does not give the balancer enough time - that one cell falls off the cliff early.

*I suggest cutting the power to the LCD screen to minimize leakage current* It may look cool but I am sure that it is power hungry.

If you are lucky you might be able to find the power traces for the chips, cut them, and fit a low cost DC-DC that would power the entire circuit from the full stack - that would minimize the current draw and imbalance.

Say there is a 5mA leakage (which sounds reasonable)

5mA/hour
120mAh per day
840mAh per week
3.36Ah per month
10Ah in three months

Here is a product with 8mA leakage - granted this has a power hungry blue LCD
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10952&Product_Name=Cell-Log_8M_Cell_Voltage_Monitor_2-8S_Lipo


If it turns out that they draw power equally from all cells then you are sitting pretty - but I suspect they did it the lazy way.

-methods

[GGoodrum]

I agree, you wouldn't want to leave a Battery Medic connected all the time, especially if you have it in the balance, mode, which brings down the level of all higher cells to the level of the lowest. Sometimes, a channel will overshoot, so that cell now becomes the lowest. This can keep happening, which would drain the cells down. I use the discharge mode, which brings all the cells down a programmable set point, and then it stops. I still wouldn't leave one connected for an extended period, but I've yet to see the discharge mode drain any cells past the set point.

The point I'm trying to make is that with LiPos, balancing just isn't required with every charge, so whatever balancer-type that is used, doesn't have to be left connected all the time, like with a regular BMS. For basic charging, the LVC/HVC part of the BMS, and the charger controller card can be used by themselves. An example of this is shown below. This is an 18s2p 66V/10Ah pack made from six Zippy 6s-5000 packs.

18s2p LiPo Pack-01.jpg

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Buried inside the pack are three 6s LVC/HVC boards, like the one shown earlier in this thread. The opto outputs from all three boards are ganged together, and brought out as a single two-wire JST-BEC plug, which plugs into a matching connector coming from the charger controller. I also brought out a separate set of 12-gauge leads for charging. These have standard 45A Andersons, which also plug into mates, coming from the charge controller. The picture below shows the charge controller plugged into the pack. Ahead of the charge controller unit is a Turnigy Watt Meter.

18s2p LiPo Pack-02.jpg

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For balancing, each LVC/HVC board has a set of 18-gauge wires, brought out of the pack, into a Molex Microfit 3.0mm 7-pin connector. As I said, most of the time, these are simply not connected to anything, but if balancing is required, they can be used to connect external balancers, such as the ones shown below. These are basically working prototypes that I put together, using modified shunt boards and end plates, from earlier versions of the 4.0 BMS unit. Shown are both a 6s and a 12s version. For my 18s pack, both will be used.

12s LiPo Balancer-01.jpg

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12s LiPo Balancer-02.jpg

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6s LiPo Balancer-02.jpg

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6s LiPo Balancer-03.jpg

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The balancer units have fans, and are completely self contained. They simply plug into the MicroFit connectors coming from the pack, whenever balancing is needed. When used while charging, the combination acts just like the full BMS, but they will also work standalone, after a charge. In this case, cells above about 4.14V will be brought down to that level.

More later...

-- Gary

[methods]

I like the idea of keeping the sensitive electronics off-board.
* Less bulk on the bike
* Less wear and tear on the BMS
* Fewer failure points at ride time

We need to find a good source for "Full Charging Solution" connectors.
I am picturing a mill-spec connector with 4 large gauge contacts and 20 - 50 smaller gauge contacts.
Something we could use to allow us to have the balancer off board but can still connect with one motion.

I hate connecting the charge leads AND a bunch of balance taps. (though I suppose having all the taps in one connector is not that bad - I am thinking of 6 JST-XH connectors for 36S)

I have seen a lot of connectors with SMA's built in but I have yet to see any with different gauge wires
(but I have not really been looking either)



Obviously it could be built up with Anderson connectors - or two different types of connectors could be "glued" together.

-methods

[GGoodrum]

Yes, connectors are always a pain, especially the smallish JST-XH variety. I also don't like the fact that they only use 22-gauge wires on these, This is fine for hooking sub packs into a parallel adapter, but for balancing, it is far better to use heavier gauge wires between the pack and whatever is used for balancing, especially with 1A+ shunt currents. There's too much voltage drop in the wires otherwise. The problem, as you know, is finding a suitable multi-pin connector that can handle larger wires sizes, and a decent amount of current. I've found two that work well, and come in various sizes, the AMP/Tyco VAL-U-LOK 4.2mm PE Series, which have pins rated up to 9A, and the Molex MicroFit 3.0mm, with a current rating of 3-5A. The problem with these is that there's the labor of putting pins on the wires. I have an expensive special crimping tool, but it is still a pain. I am able to use this same crimper on the smaller MicroFit pins, but it is even more time consuming.

There are board-mountable versions of the connectors, which eliminates having to do pins for that end, at least. What I'm doing now is having Keywin get a bunch 18-gauge multi-colored wires made up with MicroFit pins pre-crimped on each end. He couldn't source the housings over there, but all that is required is snapping in the pins. Anyway, by putting the board-mountable connectors on each end, no more crimping.

-- Gary

[liveforphysics]

I would much rather not have the balance and charge connectors all in the same plug.
I want to be able to just throw some charge in a pack with nothing more than a meanwell when I'm opertunity charging somewhere. Hooking up a balance plug and charge plug doesn't really seem like a big inconvience IMO.

[amberwolf]

Except for the cost of the connector shell/pins/etc for the opp.chg meanwell, there's nothing wrong with just using the charging pins on the meanwell connector, leaving the balancing pins open.

Unless you mean to use the same meanwell for balancing and charging when at home, in which case you have a definite point.

[GGoodrum]

Actually, I was just talking about finding good connectors for high-current balancers. You get too much voltage drop in the 22-gauge/JST-XH pigtails, even with just 1/2A of shunt current. I still run separate 12-gauge leads for the main charge current, and use Andersons for the connectors. My 18-gauge MicroFit balance plugs won't get used all that often, but when they do, I know they can handle the current.

18s2p LiPo Pack-03.jpg

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18s2p LiPo Pack-04.jpg

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18s2p LiPo Pack-05.jpg

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The MicroFit connectors have the same locking tabs as the larger VAL-U-LOK plugs, so they have the same positive connection, but are much lower profile and they come in single row variants.

-- Gary

[recumbent]

Opportunity charging is something i do often also, shopping and commuting is mostly done on my ebike in the summer.

Charging without balance leads is perfectly fine (in the field) with a $60 bulk charger in the pannier using some sort of monitor like the Cycle Analyst or CellLog.
The 18awg Microfit connector for balancing is a good idea but carrying the expensive balancing charger or other means is not practical (in the field), yet.

Although I like the black Microfit connectors, and with 18awg wires, we could charge and balance through just the balance leads with modest current, i hope.

[methods]

we could charge and balance through just the balance leads with modest current, i hope.

I actually drew up a 12S charger that is nothing but an array of 4.2V isolated DC-DC converters - input is 12V to 38V, output goes directly to the balance taps. Similar to what people are doing with these "cell phone chargers" but cheaper, on a PCB, and with a DC input. You could leave it attached to your pack (serving as a parallel connector board) and then opportunity charge with whatever you can find - a car battery, a Lead charger, a laptop supply, a rectum fryer, etc.

Talk about opportunity charging. . .

-methods

[recumbent]

... You could leave it attached to your pack (serving as a parallel connector board) and then opportunity charge with whatever you can find - a car battery, a Lead charger, a laptop supply, a rectum fryer, etc.

Talk about opportunity charging. . .

That would be so economical charging with a laptop charger if possible, while we park our ebikes. Great idea's you put together Methods.

Now all I have to is assemble a bunch of 8 series Microfit, or HX connectors with my new crimper from Westmountainradio.
Hope it's not too difficult if i use the correct die attachment i've also ordered.

[Hyena]

I actually drew up a 12S charger that is nothing but an array of 4.2V isolated DC-DC converters - input is 12V to 38V, output goes directly to the balance taps

Cool, I was looking at making something similar in 6S guise to plug into the balance tap of each pack for a short period of time to balance them if needs be. Got an online source for these ?

[Ykick]

we could charge and balance through just the balance leads with modest current, i hope.

I actually drew up a 12S charger that is nothing but an array of 4.2V isolated DC-DC converters - input is 12V to 38V, output goes directly to the balance taps. Similar to what people are doing with these "cell phone chargers" but cheaper, on a PCB, and with a DC input. You could leave it attached to your pack (serving as a parallel connector board) and then opportunity charge with whatever you can find - a car battery, a Lead charger, a laptop supply, a rectum fryer, etc.

Talk about opportunity charging. . .

-methods

How would these things work?

http://www.callpod.com/products/chargepod?tab=demo

I wonder if they could be readily adapted?

[liveforphysics]

These will do what Methy described. 4 isolated 4.2v CC/CV power supplies in a case. Buy 3 of them to perfectly balance charge a 12s pack, but 6 to perfectly balance charge a 24s pack. These things are tiny.

Or, even cheaper:

http://www.hobbycity.com/hobbyking/stor ... rger_2S-3S

Those things are $4.25 each, and contain 3 isolated DC/DC converter CC/CV power supplies inside a little box scarcely larger than a matchbox.
For $20 (for a 12s pack) or $40 (for a 24s pack), and some time wiring up the required JST connectors, you can have 800mA balance charging to perfectly balance charge a pack no matter how off the voltages were when you started. You could power them all from a laptop charger.

It would be useless for opportunity charging on large packs due to the slow rate, but for something like putting a pack in balance, just plug them in and leave it overnight, and the next daay, all cells would be sitting right at 4.2v.

[Hyena]

Those things are $4.25 each, and contain 3 isolated DC/DC converter CC/CV power supplies inside a little box scarcely larger than a matchbox

Sweet, I didn't realise they were isolated I take it they can charge through the balance taps only then without the main discharge leads being connected ?

[liveforphysics]

Those things are $4.25 each, and contain 3 isolated DC/DC converter CC/CV power supplies inside a little box scarcely larger than a matchbox

Sweet, I didn't realise they were isolated I take it they can charge through the balance taps only then without the main discharge leads being connected ?

That's right. You don't use main charge leads. You charge entirely through the balance taps. This method is no replacement for the type of charging you can do with a setup like a meanwell and Garys balancer, because its limited to the current that can pass throught the balance taps, so 20Ah packs take like 24hrs to charge.

What it is good for though is taking a pack that is out of wack, and over the course of a day or so, you can return all cells to perfect balance.
A BMS struggles to find balance if it has a few very low cells. A setup like this doesn't matter if you have some cells at 4.25v, and some cells at 2.8v, it charges each one seperately, and doesn't know or care what any cells happen to be at, it just slowly raises each one to 4.2v through the balance taps.

[Hyena]

Nah that's cool, it's exactly what I want. I have a few on the way, thanks for the tip
My packs don't ever get out of balance anyway with parallel charging in banks of 6S but I've built a few 10s and 12S packs for other people that have gotten slightly out of balance (delta v of 0.05 -0.1v) over a few weeks of charging with a meanwell at full pack voltage. I've set the charge voltage conservatively so even with a delta V of 0.1v it can't exceed 4.25v/cell (unless one dies) but I'll use these to periodically 'service' their packs (currently using a batterymedic which takes all day)

I guess being isolated you could also wire the 3S outputs in parallel to create a 2 amp single cell charger ?

[liveforphysics]

I guess being isolated you could also wire the 3S outputs in parallel to create a 2 amp single cell charger ?

You could just get the first one I linked that does 2amps.

2amps really is about the limit you can do through the balance taps though.

I've got an old-school little charger that does up to 6s through the balance taps at 2amps. It cost me like $160 about 6 years ago. lol Inside, it's just 6 little 2amp DC/DC converters.

This ultimately is nothing new, and it's nothing different than the guys who buy a whole bunch of the little cell-phone chargers to charge, or the guys who use the Vicor DC/DC power supplies to charge. Using these little hobby guys has good and bad sides. Advantages are it's dirt cheap and very light and compact. It's disadvantages are that it's so slow, it makes it useless for normal EV use, because charge times in the 24hr range just don't fly for a typical E-bike application.

It's more like a tool to fix a pack that you F-up rather than a charger.

[andreym]

Hi!

Did anybody get already those 8S lipo from HK? Tests/reviews???
I also ordered 4 of these
and they only shipped yesterday - order was placed about 26-th of march

Garry, are you planning to make your LiPo charging/LVC system for 8S available on tppacks? If not, can I ask you to make 3 8S modules + current limiting module for me (assembled or not = does not matter) and tell me where to send the money for it?
It would be great to get it with BMS v4 for 24s lifepo4 i asked you about by e-mail.

Regards,
Andrey.

[recumbent]

Hi!

Did anybody get already those 8S lipo from HK? Tests/reviews???
I also ordered 4 ...

You mean these? Got them couple days ago and were perfectly balanced to 3.88v each cell.
Left the CellLog plugged in for three hours and didn't shift voltage, but the JST-HX connector was a tad warm.

[liveforphysics]

Thats a 512watt-hour LiFePO4 pack and a 515watt-hour LiPo pack.

That picture does a VERY good job of showing the size difference between cylinder LiFePO4 and Prismatic.

[GGoodrum]

Garry, are you planning to make your LiPo charging/LVC system for 8S available on tppacks? If not, can I ask you to make 3 8S modules + current limiting module for me (assembled or not = does not matter) and tell me where to send the money for it?
It would be great to get it with BMS v4 for 24s lifepo4 i asked you about by e-mail.

I am doing 8s versions of the new LVC/HVC/6s4p parallel adapter boards, just waiting on the PCBs. I already have the 9-pin JST-XH and 9-pin Microfit connectors.

Tomorrow I will start making the 6s versions available, along with the small charge controller units and Battery Medic booster kits. Just finishing up the connection instructions/user manual for all three, and the website updates. I'll add the 8s version as soon as I get the boards, which should be Wednesday or Thursday.

-- Gary

[GGoodrum]

Here is what the 6s and 8s boards look like:

6-8-Cell LVC-HVC-v4.0.7.png

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I'm finishing up the website updates, but the 6s versions will be available later today, along with the Charge Controllers and the Battery Medic Boosters. The 8-channel version of the LVC/HVC/8s4p Parallel Adapters will follow in a few days, when I get the PCBs back.

-- Gary

[chroot]

Sweet! I want buy few couple 6s LVC/HVC.

[nomad85]

I'm finishing up the website updates, but the 6s versions will be available later today, along with the Charge Controllers and the Battery Medic Boosters. The 8-channel version of the LVC/HVC/8s4p Parallel Adapters will follow in a few days, when I get the PCBs back.

-- Gary

Gary, will these work with 5s packs? I just ordered 9 of them
Are these (parallel boards and charge limiter) parts of the bms or is everything separate?

[geoff57]

I'm finishing up the website updates, but the 6s versions will be available later today, along with the Charge Controllers and the Battery Medic Boosters. The 8-channel version of the LVC/HVC/8s4p Parallel Adapters will follow in a few days, when I get the PCBs back.

-- Gary

Gary, will these work with 5s packs? I just ordered 9 of them
Are these (parallel boards and charge limiter) parts of the bms or is everything separate?

hi
looks like they are like the old lvc boards on the web site in that you can fit up to 4 JST HX balance connectors to the board mine was for 5S packs and I am sure that that gary will have covered for that with the new boards it has with the new boards a LVC cutoff for riding and a HVC cutoff for charging the packs at one end of the board a molex connector can be fitted that can handle a higher current than the JST HX connectors this is for the battery medic with booster kit to be used to balance the packs according to gary not needed to be used every time.

I'm going to want 4 for my battery pack with at least 1 battery medic booster kit and the small charge controller units enough for a 20S pack.

Geoff.