Can I use the balance port to improve accuracy for 1S parallel charging?

[clough42]

I just built a 1S parallel charging board to charge 12 mCP X batteries simultaneously and I'm wondering if I can connect a balance plug to the charger to get better accuracy. The charger is a Venom 2-10.

While charging 10 batteries with it last night at 3A, I noticed that I'm getting about 30mV voltage drop between the 4mm banana jacks at the charger and the battery connectors. That equates to about .01 Ohm resistance, which I think is acceptable. This difference drops, of course, during the terminal CV charging phase and the batteries end up resting around 4.18-4.19V.

But when discharging to storage, the charger doesn't appear to be reading the voltage as accurately. When the charger reaches its final voltage of 3.8V, the cells are still at 3.9V. I have verified that this isn't resistance in the charging board. If I pull the banana plugs out of the charger slightly and probe the connectors with my meter, it reads 3.9V while the charger display is reading 3.8V. 3.9V should be acceptable for storage, but I'd prefer that the charger actually reach the programmed voltage.

Can I build a balance cable that connects to the first two pins of the balance connector to provide a low-current voltage probe to the charger? Will the charger use it for 1S charging/storage?

[desertstalker]

Its likely that the charger is putting enough load on the batteries that they will drop voltage, so the charger cuts of and then the voltage recovers. Does the charger you use allow you to have it reduce discharge current as it hits the cutoff (ichargers do)?

[DominicD]

They are cheap 1s packs bud, don't over-think it, just use and enjoy them

[clough42]

Desertstalker, that was my initial assumption--that the voltage was sagging under load, but I don't think that is the case. I probed the banana jacks at the charger during discharge, and the actual voltage was .1V higher than what was being reported as the current voltage on the charger display. The Venom charger does back off the discharge current as it approaches cutoff. I suspect it's switching to CV at the end.

The charger manual says that it uses the balance plug during storage discharge to keep the pack balanced. I'm wondering if it can also use the balance plug to monitor the single cell's voltage when discharging 1S.

I don't want to go to the trouble of getting the connector and building the cable if someone could tell me that these chargers explicitly ignore the balance input for 1S.

[The WoodCrafter]

I would bet money that the port does nothing with a 1S pack.
THERE IS NOTHING TO BALANCE IT TO, YOU HAVE A 1S BATTERY.

If you really want your packs at 3.85V lower the cut off voltage to amount of the spring back after the load is removed. (.05V)

[clough42]

Yes, I'm aware there's nothing to balance. There would be some advantage to having a low-current circuit for voltage measurement. I'm just looking for someone who knows if this charger will take advantage of it.

It appears that the recent Hyperion parallel charging boards have a seventh, smaller connector on them and got the impression that this is for such a use. If there isn't anyone here who knows for sure, maybe I'll just try it and report back.

[clough42]

Well, I tried it and it looks like the answer is no. Hooking up the balance port doesn't improve accuracy. Also, the charger doesn't allow you to select cell counts less than 2S when in balance charging mode, so that pretty much sums it up.

[ahahn]

On my Powerlab 6s it does work. However I put a balancing connector on my parallel adapter really for another reason. My Multi4s charges only through a balance connector, so when I use that charger, I use the balance connector. My Powerlab 6 charges only though the main discharge leads. On it, I can charge either in a non-balanced mode (without balancing connector plugged in) or in balancing mode (with balancing connector also plugged in).

But I wouldn't worry about +-0.1V for storage mode. It doesn't matter that much. As long as it isn't fully charged or fully depleted, you are in pretty good shape.

[DoubleCH]

My GT Power A6-10 charger will monitor balance port voltage if used and will ignore otherwise. Depending on charge current, the voltage difference between the charger reporting voltage from banana plug and balance port vary. Charging current reduces if any of the voltages reaches 4.20V. However, it seems like there might be different algorithm to determine when charging session ends depending on whether balance port is used because even though during 1S charging the balance port voltage never exceeds that of banana plug's, charging session always finishes sooner with balance port connected ending up around 4.18-4.19V, or finishes at 4.20-4.21V without balance port connected.

[Gregor99]

Originally Posted by everydayflyer

The only Multi chemistry hobby chargers I own which will charge a 1S to a resting 4.2V per cell without using both main leads and balancing leads are the FMA PL8 and PL6. My son has my CP4 and I have never used it with a 1S and I have not tried either the CP10 or CP XP either.

I do know that icharger 208B ,306B and 3010B as well as Hyperion original DUO and two Hyperion 720s Net as well as TB 820 all have the same issue. If used with main leads only cell wil be aprox. 4.15V at end of charge and if main leads and balancing leads are used in parallel cell will be at 4.2 . This is really not an issue as 4.15 is kinder to the LiPolys and is still 95% state of charge and is faster also.

It is only 1S and 2S Lipolys which do not have dual lead sets other than the few which have no balancing leads at all.

If you have an iCharger and a 3S or whatever with main and balancing leads it is simple enought to do a non balanced charge and check cell voltages,then do a balanced chatrge and check cell voltages.

Another fact is that the Hyperion chargers will not do a Storage without the balancing leads even on a 1S but then the PL8 has the same issue if using Storage Preset at least on a 2S using JST - XH balancing connection mode.

Charles

http://www.rcgroups.com/forums/showp...0&postcount=13

[Harrow]

The charger is always going to finish the charge cycle in Constant Voltage mode and charger until current reaches 10% of initial charge setting, so there is nothing that the more accurate voltage reading could be used for anyway. The only way it would be of any use would be if the charger put out greater than 4.2 volts, and I don't think any charger manufacturer is going to do that for safety reasons.

At the low end of the charger cycle, the voltage drop should be very minimal anyway.

[Gregor99]

The charger is always going to finish the charge cycle in Constant Voltage mode and charger until current reaches 10% of initial charge setting,
That depends on the charger. Most of the better chargers alow for adjustment of this setting. Is usally use C/20 with my 1s cells (one fifth of the set current).

So there is nothing that the more accurate voltage reading could be used for anyway.
As already stated, it could be used for an accurate reading of the cell's voltage. If there is any current at all, there will be a voltage drop caused by the wires. If the charger is using the 4-wire Kelvin method, the actual voltage of the cell will always be lower than the charger can detect. Some chargers use periodic momentary pause in the current for voltage detection. This way there is no requirement for the second set of wires.

More about the 4-wire Kelvin method. http://www.allaboutcircuits.com/vol_1/chpt_8/9.html

At the low end of the charger cycle, the voltage drop should be very minimal anyway.
Depends on the "definition" minimal. While many would consider 0.05v a very minimal value, some would complain that thier LiPos are not fully charged at 4.15v. While they would be correct, its actually better for the battery to undercharge it slightly.

Regardless of whether you like your batteries charged to 4.2v or 4.15v some chargers clearly have voltage reading errors when using only a single set of charge leads. Not that we should be terribly concerned about a slight undercharge. But certainly we should be aware of it.

[clough42]

Thanks for all the input. I may fiddle with it a little more. I did notice that I'm getting better results when charging a bunch of batteries in parallel than if I charge just one. I suspect I'm running into the minimum current measurement resolution of the charger.

I agree that a slight undercharge isn't a problem. I just measured and after the factory-recommended 4:00 of hovering, I'm putting about 90mAH back into my 300mAH mCP X batteries. Lots more headroom there until the day that my thumbs suddenly start showing some talent.

[desertstalker]

My i charger 106B charges my MCPX packs to 4.19V using only the main leads. The same place all my 2,3 and 4S packs end up.

I dont exceed a couple of Amps though, charging 6 in parallel.

[Harrow]

Gregor's points are interesting to note, and technically correct. However, I have plenty of single cell planes (as little as 20 grams) and in practice the charging always gets to around the 4.18 or 4.19 level. Given the size of the aircraft that use single cell batteries, I really think it is not worth worrying about. You are going to get a lot more variation in flight time from how you fly than from the variation in charge voltage you will get from any practical charging setup.