AIRPLANENUTS

My Feedback: (2)

Guys, I am trying to charge two nimh packs, both plugged in to a Futaba 8 ch pcm rx via Futaba heavy-duty switches. The charger is the Hobbico Quick Field Charger MkII, and although the manual states that the two charging circuits are completely independent, I fear they are seeing a common ground bus via the rx. I can charge the packs separately, of course, but in order to charge them simultaneously, should I wire the charge leads directly to the battery packs, and if so, will the charger still see the common ground, assuming this is the problem?

Any suggestions would be appreciated.

Rick

Rodney

Unfortunately, you will still have a common ground problem as long as they are both mounted in the plane as the grounds for both batteries and the receiver are common, even with the switches off as only the hot or positive side is switched. You must break the ground circuit between the two batteries in order to charge with your charger.

AIRPLANENUTS

My Feedback: (2)

Rodney, you are exactly right. I just finished a little experiment - when I disconnected the ground momentarily on one pack, the charger started peaking both packs simultaneously. I reconnected the ground during the charge, and the charger kept on charging. So, it definitely is a common ground problem, but odd that only a momentary ground disconnect allows the charger to begin peaking both packs at the same time. The manual states that each port is completely independent of the other, but apparently, that is not the case.

I wonder if I could reverse the positive and negative wires inside the switch, thereby breaking the circuit on the negative side?

Thank you for the information, Rodney.

Rick

Rodney

I'm not sure of the internal circuitry of your charger but I'd be careful about reconnecting the common ground while charging even though it started when you disconnected the grounds. The manner in which your charger detects peak charge will most probably be compromised if you reconnect the grounds while charging. I would recommend that you always keep the grounds isolated while charging.

AIRPLANENUTS

My Feedback: (2)

Thanks Rodney.

Problem solved. I re-wired the Futaba heavy-duty switch, which is actually serviceable, to switch the ground instead of the positive, and this allowed both charging ports to work simultaneously.

AIRPLANENUTS

My Feedback: (2)

Well, I may have been hasty in thinking the problem was solved.
Although the charger will now charge both batteries simultaneously,
it is not peaking both packs. So, if the switch will allow it, I will
re-wire it so that both the positive and negative sides in the circuit
are disconnected. If not, I will find a switch that will.

Apparently, the positive side is causing this little problem,
because when I only charge one pack at a time, the peak charger works
correctly.

Livin' and learnin'.

AIRPLANENUTS

My Feedback: (2)

Anyone ever have any problem w/arcing after soldering both positive and negative leads to a DPDT switch? I'll be wiring the charge lead to one end of the switch, the battery to the middle, and the receiver lead to the opposite end of the switch.

Thanks,
Rick

Flying Geezer

My Feedback: (14)

When you tied the postive side together you ended up with two chargers in parallel. You eliminated the common ground, but when one pack peaked, it shut off one charge circuit, the reduced current dropped the voltage of the second charge circuit, and then it peaked.

To meet you goal you must complety isolate the positive and negative of both packs with two DPDT switches or by unplugging one pack. Or get a charger with no common ground problems.

AIRPLANENUTS

My Feedback: (2)

Ah, thanks Geezer. Well, before I read this this morning, I re-wired the one Futaba heavy-duty switch, which is just a DPDT switch with a fancy case, with the positive leads on one side and the negative leads on the other, thus breaking the circuit completely to the receiver.

The other Futaba heavy-duty switch is untouched, meaning the factory wiring of breaking the positive side and tying all the negative leads together.

Will this present a problem?

Thanks,
Rick

Flying Geezer

My Feedback: (14)

I posted 2 DPDT switches but that's not correct. I over stated the situation. With just one DPDT as you are planning will isolate one battery pack completly. As long as the positve and negative wiring of the batteries are totally disconnected you're ok to go.

Sorry for the over-statement.

AIRPLANENUTS

My Feedback: (2)

Thanks, Geezer! I had no idea this was such a problem - apparently Hobbico's statement that each charging port is completely independent of the other is a falsehood.

Rick

Rodney

What they mean by independent is that you can program each output individually, i.e. different battery types, different cell count etc. They do not mean that there is no interconnecting circuitry, after all, there is only one power supply be it internal or external.

AIRPLANENUTS

My Feedback: (2)

Rodney, that makes perfect sense. I didn't think of it in those terms.

Thank you.

AIRPLANENUTS

My Feedback: (2)

Okay, guys, found another problem. The Hobbico Quick Peak Charger MkII has this timeout
feature - 120 minutes for nimh/nicd & 180 minutes for lipo/li-ion. So, if you want to
peak charge your 2000 mAh nimh from a full discharge, you have to charge them at a rate
of 1 amp or more - not very good for the health & longevity of these cells.

Anyone know how to disable/lengthen this feature? Hobbico says no-go, so this is just
a shot in the dark.

Thanks,
Rick