karasr

My Feedback: (1)

I have a Smart Fly SuperReg installed in my jet. I use 2 Apogee 2200mAh 2 cell batteries plugged into the SuperReg.
When I try to charge the batteries using the node connector on the Apogee batteries I get a "reverse polarity" error message.
I can charge either battery on one input of the Cellpro 10s but, not both together.
When I disconnect the batteries from the SuperReg the Cellpro works fine and charges both batteries at once as it is supossed to.
The regulator is buried deep inside the jet and it is very inconvient to disconnect the batteries from the SuperReg.
I have talked to Nathan at FMA many times and am on my second Cellpro.

Bob K

rrritchey

Hello Bob,
This is called the "common ground" problem. Anytime you connect two batteries to the same place you end up with a ground short between the batteries. Even mechanical switches do not switch the ground wire, you still end up with this problem. Because the charge senses the current it is delivering on its ground wire instead of its positive lead when you try to charge two batteries the charger gets confused. Unless you have a charger that senses current on the positive lead there is now way around this. Your only choice is to break the ground by disconnecting one battery from the circuit. Let me know if you have any more questions.

karasr

My Feedback: (1)

Thank you for your super fast reply!
I am sending this on to Nathan at FMA.
Perhaps they can get around this.
If not, I will just 'bite the bullet' and disconnect one battery.
Thank you
Bob K

Zeeb

My Feedback: (41)

Bob K,

I'd be very interested in what Nathan has to say about this issue. I spoke with him quite a bit late last year when they were doing the programming for the 10S. He told me at that time it would not be difficult to do, but didn't think there was enough room in the charger's chip to make the changes in programming.

I told him there would be a bunch of RC guys who'd be very appreciative of such a change, but when the charger came out it obviously does not have the capability. Since it is Internet upgradable, maybe they're working on something?

Oh for what it's worth, I never did have much luck getting ahold of Nathan via e-mail but he's not too tough to find if you call FMA....

rrritchey

Hi Zeeb,
I really doubt they can do this in software. It has to do with how they sense the amount of current they are supplying to the batteries. When you have a common ground system and try to charge both batteries, the ground current coming out of the two batteries combines and then goes back to the two chargers or the charger's dual outputs. Depending on a lot of issues, the charger may be putting in one amp on the positive lead but it may read a return current higher or lower than that, causing it to try and compensate. This is due to minor variations in the connectors and wires. Unless you physically sense the current on the positive lead there is no way to accurately know the current you are sending to the battery when you have a common ground system. Let me know if you have any other questions.

Zeeb

My Feedback: (41)

Thanks for the note Bob.

Yeah that was my impression, you need a high side sense charger to accomodate the common ground issue.

I was just relaying what Nathan told me, probably late November or early December last year. It didn't make any sense to me at the time, but I'm no electrical engineer. So I would be interested in what he tells Bob K about the issue if he does get back to him with an answer.

karasr

My Feedback: (1)

This is the latest from FMA on the Cellpro.
Don't get me wrongit is a great charger but, this common ground problem is, I imagine, quite common (no pun intended).



Hi Nathan:
I imagine you mean for me to make a "Y" connector for the node connectors.
Then I would not be able to balance all four cellsAm I thinking correctly?
Bob K
- Original Message -
From: Nathan Gwozdecki
Sent: Monday, October 06, 2008 11:51 PM
Subject: RE: Cellpro 10s Reverse polarity?


Hi,



See if the smart fly regulator will parallel the two packs on the positive side too. If it does, then you can charge both packs as a 2 cell 2P battery on channel 1. The 10S is a series charger. It could have been designed to charge parallel or series, but it is too late for that now. At least the charger errors out and protects itself from damage J







Thank You,

Nathan Gwozdecki

Design Engineer, FMA Inc.

rrritchey

Hi Bob,
You could make a Y adapter but you are right that you could not then balance all the cells. For each cell in parallel the one that charges the fastest would dominate and you could end up with two packs that only partially charge because one dominant cell is in one pack and the dominate cell is in the other pack. Sorry I don't have a good solution. There are only a few chargers, like the Fromeco cube, that handle the common ground correctly.

Zeeb

My Feedback: (41)

Well that answer from FMA was kind of what they told me.

Dick Hanson has been building up some Y setups for guys, but you still have to disconnect one battery to do it. The Fromeco will charge 'em with the common ground, but if you have to buy the Cube and the A123 card for it, it is spendy and it only puts out 2.5 amps. So my thought is that I'll just continue doing one battery at a time with the CellPro as the charge rate is so much higher, IIRC you can do 4 amps through the balance leads just like I was doing with my CellPro 4S chargers.

Thanks Bob K for the update, and thanks Bob R for letting me chime in and ask questions of another member.