Im not going to bother with a BMS

[DrkAngel]

• I have variously described a BMS as:
• An expensive security blanket;
• A Band-Aid for a defective pack:

Back in 2008 I utilized a BMS w/equalization (PCB) on my 1st 18650 (recycled cells) builds, but quickly became disillusioned by its limitations and expense.

After developing "proper" cell testing and matching methodologies, I was very satisfied with bulk charging and cell level monitoring.
Those 1-8s voltage monitor alarms are an absolute bargain!

 

[Jestronix]

How often would u say with all new cells and staying above 20% discharge and below 90% charge that one would need to be balancing cells ? I know on my RC packs they needed balancing every 4th run, but they were HK packs.

How likely is a balance board going to have the time to balancing things out ? They are usually tiny trickle 20ma balance bleeds taking days to balance out our packs. Meaning u need days for things to balance, which is fine on tool batteries where u may leave the pack for a week or two.

For ebikes and charging outside and attended while charging I see almost no need for a balance board.

That being said, if I had 5+ grand ebike or a 20k motorbike , err I'd be hunting out a very expensive BMS yeh ?

 

[dogman dan]

If you HK cells need balance every 4th run,, then you are beating them like the dog that shit inside your shoe.

Same will result with any other cell you beat. Discharge rate + depth of discharge my man. Get that pack all hot,, bet it needs a balance. Maybe you just define balanced different than I do.

Don't need to undercharge to keep the balance,, the undercharge is to give you the head room to call .05 off plenty balanced enough when naked charging. If you want your pack to stay balanced to .01, then A you need more accurate measuring device than any hobby charger, and B, you need balance every cycle.

The way I use my hobby king shit,, I balance about 4 times a year. Generally, I never see "unbalanced" even then,, which I call .1v off.

I use an RC charger when I do balance, but not like you think. I just discharge one high cell, or charge one low cell. Generally in a 14s 2p pack, I might find two cells that need adjustment. Charge or discharge the off cell through the balance wires. On the road, like on a tour,, discharge a high cell with a 12v light bulb.

Oh,, and unless somebody out there hasn't read it yet,, store and charge your naked packs, like HK cells, where you would willingly build a fire.

 

[izeman]

It's common to discharge rc-lipo until NO charge is in it. Most cheap controllers have a set lvc of 3v/cell. So no wonder those batteries run totally out of balance.
Discharging them to 3.6v under load should keep them balanced for a while.


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[Jestronix]

Yeh I did beat the shit out of them, 10c runs on their claimed 20c peak packs would very quickly see very hot packs. Their packs were happy at 5c and under, how they advertise them the way they do is >~^}£#. But, I bought cheap multistars, nanotech and now their graphite, I mean graphene named batteries, may be better.... I used to actually see packs drop cells even when not in use , I bought 16 packs , 8 are dead in maybe at best 30 cycles and some 3 or 4 cycles. I had ones die when I was running 5c max too. I refuse to use RC packs again, if I ever do it will be with the idea of throwaway performance needs.

Balance was ok 1 to 5c and 1c charge

 

[Ykick]

Well, on that note here’s an old graph (many regulars have seen before) visually demonstrating the “cliff” when reaching low state of charge for Hobby RC Lipo:

These tests were conducted using 2qty Turnigy 20C 5Ah 4S Hardcase series wired for 8S driving a resistive load between 5-7A.

As you can see, there’s not much energy left below 3.55V/cell. Trouble is, some cell will drop off much sooner than others. Users need to play conservatively in this range of deep discharge.

Most of us don’t venture there too often. Or if we do, we’ve learned to immediately take a look and see how the balance is holding up after running into controller LVC.

Dogman’s advice for balance charging is the best way I’ve found as well. I hardly ever connect my RC Charger using main leads and balance connectors. Only for loose packs that haven’t been configured into larger series string for Bike pack. Or when I 1st receive RC Lipo packs and give them a full cycle and IR test.

Over the course of use, I just pump up/down single (1S) cell if/when needed. Never breaking the pack completely apart unless there’s some obvious problem which needs attention.

 

[parabellum]

HVC 4.1V/cell, LVC 3.6V/cell (Mostly, I do not get lower than 3.8V/cell) and I balance few times per year. Cheap (4 years old) 4s HK hard cases and do not beat crap out of them C rate wise.

 

[Jestronix]

So the single cell discharge method, what sort of connector do you use, JST and connect what ever pins ?

 

[DrkAngel]

I use similar to 50 straight pin connector , cut 2 pins, bend contacts apart (on one end for alligator clips from charge\discharge device) and insert into proper cell on balance connector.

• With my 26-32Ah packs I discharge using:
• jumpers to legs of soldering gun tip
• 3d printer heat element in bottle of water

 

[Ykick]

So the single cell discharge method, what sort of connector do you use, JST and connect what ever pins ?

Very complicated, haha:

Works for charging low cells in series strings too. You gotta figure out the correct pins/cells you're taping into but that should be obvious.

Depending on your RC Charger (or some other 1S charger) and your bulk charger it's a good idea (possibly grounding issues) to never attempt to do both at the same time.

 

[phild]

1) The BMS gives you no visibility as to where the individual cells are at - you need the 1-8 cell LEDs to give you voltages otherwise the battery is a black box.
2) There is no balancing going on with a BMS if the pack is not fully charged - we don't want to fully charge to maximise the life of the pack!
3) My controller has a low voltage cut off already I don't need to duplicate this in the BMS (although maybe the BMS is looking at each cell's LVC?)

Since I only charge to 80% and currently without the 1-8S LED voltage readouts (on order now) I have to resort to getting my pack out of my triangle bag, rolling back the insulation (neoprene cover) pulling the balance lead out of the BMS them a multimeter check on each cell... then discharging individual cells as required to balance ... MAD!!

The ideal solution is to ditch the BMS and have a 14S (in my case) balance charger so we simply hook up the positive/negative and a balance lead and we then get a display of the charge state of all cells - perfect - much as the RC folks do even for their small batteries! BUT the ThunderPower is no more the Hyperion 1420i is no more - there is a gap in the market here.

wire.rat
I just bought a RadioLink CB86 Plus 6A 210W Lipo Balance Charger that has 8x 6S charging ports

http://www.banggood.com/RadioLink-CB86-Plus-6A-210W-Professional-Lipo-Balance-Charger-Discharger-p-972541.html

Maybe this is a solution? I'd have to make two 6S balance leads and one 2S balance lead and 3 sets of charging leads for each sub-battery and just hook up the 6 charging leads and 3 balance leads for each charge. We are still waiting for a 14S charger - when we have such products as the satiator but no easy large pack balancing choices?

Very interested to hear how you get on with this charger wire.rat!

 

[dogman dan]

That's about the same thing I use for single cell charging and discharging. Two male prongs one end, whatever plug you have on your RC charger on the other end.

Out in the wild, on a bike tour I just carry a turn signal light with the two male jst's attached. Then if I drive my pack out of balance making it to the next town, I can charge up, then discharge any cells that run high with the light.

You can add a set of balance ports to the battery. Just a y connection on those wires to the bms,, then some jst plugs. Then you can just fish out those plugs, pop in your cellog 8 and look at each cell.

Very interesting to watch that bms work when it's balancing, by watching the cellogs. Soon you know just which cell you are unbalancing every ride, and can compare lower DOD discharges with shallower ones, and figure out where your pack is right now. What end of ride voltage to stop at, if you want it to stay balanced.

IMO,,, EVERY lithium battery with bms should have a diagnostic port that allows connecting a device like a cellog 8. If for no other reason, so a vendor/bike shop tech can tell when a pack just needs a balance charge, and when it needs a warranty replacement. Later on, out of warranty, it would still be good to be able to confirm that the pack has a dead cell without yanking it out of the case. Its just dumb right now.

Re chargers, lots of people run 12s just so they can use the thunder power charger, which charges each cell individually for a fast and perfect balance charge every cycle. This beats a bms by a mile for balancing.

What a bms does,, is shut off charging when your weakest cell is full. Your weak, low capacity cell is the one that gets charged fullest, which as you know, is not ideal. So even if you turn your charger down half a volt, that shitty cell still gets to charge to 4.2v because it fills 30 min before the others.

 

[Jestronix]

Any issues with running cell monitors 24/7 ? I guess they take power from the first two pins ? Thus draining those cells, I would need a switch that could flick a 4 small relays when the main power is turned on, and I guess when charging. A lot of wiring but could be set and forget. Long as the relays don't effect voltage readings. I'd love to have the alarms hooked to the aux on my ca, that could cut power or change power output

 

[DrkAngel]

1-8s voltage monitor-alarms do draw current continuously from s1+s2.
Disconnecting pin 1 negative, (switch works fine) effectively disables any current drain.
Can also be used as full voltage monitor-fuel gauge, up to 8s 33.6V, connected to throttle led power, with minimal pack drain.

Note - purchase multiple! Quality control-accuracy varies between individual units. Confirm voltage accuracy of each bank. Some units have varied ≤.02V from actual.