Ernie Misner

Greetings,

I have a question about the proper function of a standard (no negative pulses) peak detection charger WHEN a diode is in the circuit as comes with the Futaba 6XA transmitter.

I know that the diode can be jumped when using a reverse pulse charger such as the Sirius, but I did not think the diode caused a peak charging problem when using a standard peak charger until I read a comment on the Sirius Charger home page. They state that no charger can properly peak detect when a diode is in place. (because of improper voltage feedback I assume)

Huh, really??? Are all the folks who are peak charging through a diode risking their batteries and planes? I would appreciate any comments on this!

Ernie

Lynx

The only thing you have to remember is that there is a voltage drop over a diode. Depending on the diode it'll varry somewhat. Depending on what kind of charging algorythm your charger uses it will or will not have a problem. Only 'stupid' chargers should be affected. IE one's that peek detect based on static voltages, as opposed to checks for the true voltage dip seen when a pack hits it's full charge.

Geistware

My Feedback: (16)

Peak chargers work with the diode installed, or at least the ones from hobbico do.

causeitflies

like these?

Lynx

hahahaha. You forgot to blurr the "Stupid" =) But nice picture anyways =>

causeitflies

Yeah I did it real quick.

Geistware

My Feedback: (16)

WHy is the hobbico charger stupid?

causeitflies

Just using Lynx's example "Only 'stupid' chargers should be affected. IE one's that peek detect based on static voltages, as opposed to checks for the true voltage dip seen when a pack hits it's full charge."

My old Hobbico charger will work through a diode but it is "old". The Smart Charge actually reads the voltage and therefore won't work through a diode. It doesn't really read a peak but predicts the right charge The old hobbico seems to work just fine but I have a suspicion it slightly overcharges and then senses the peak. So, I use it sparingly.

Tim_Indy

Hmmmm. Guess my new Great Planes Triton and my FMA Super Turbo are stupid chargers, because neither will charge through a transmitter diode. They won't start a charge unless they can sense voltage, and the diode in the circuit prevents voltage from flowing out of the transmitter, so there's nothing for the charger to detect.

Additionally, how can a charger check "for the true voltage dip seen when a pack hits it's full charge" when a diode in the circuit prevents outflow?

Maybe it's just ME that's stupid!

causeitflies

Tim_Indy
I think you misunderstood.

Tim_Indy

Yeah, I see I did.

Geistware

My Feedback: (16)

Get a 9C and never worry about that again.
Tim, I know you have/had a 8U.
Can it be updated with the circuit that is in the 9C?

Tim_Indy

Hey Miles, I have 2 Super 8 Futabas. I have no problem with the diode, I just jump it with a single strand of servo wire, and have zero problems with peak charging.

I had considered a 9C but the only advantage I see is that it has provisions for triple rates on a switch. My 8U will also do triple rates, but it takes a mix to do it. I never need triple rates anyway, so the Super 8s are fine for me.

You coming up shortly?

GalenB

My Feedback: (18)

Yes! I had my "jumper" replaced with a poly switch last year when I had my transmitter tuned. I had Peter Waters at KMI do the work, but I think Radio South and Hobby Services will do it too...

Ernie Misner

There is another whole reason why the Sirius type smart chargers will not work through a diode. They are a pulse charger that emmits a "negative flow" pulse at times that could not pass through the diode.

I wrote to MRC who manufacture the 956 Super Brain charger. Tim wrote back and said that their charger relies on "feedback" from the battery that would be impossible with a diode in place.

I now believe that every other high quality peak charger would not work properly and consistantly (if at all as mentioned above) with a diode in the charging circuit.

I sure do appreciate all the informative replies to my question on this subject..... thanks to all.

Now, I've forgotten, what does a poly switch do exactly? .... and why would it be better than simply jumping the diode?

Ernie

Ernie Misner

Tim, a single strand of servo wire would be teeny, teeny, wouldn't it? Wouldn't all the charge current have to pass through such a tiny piece of wire? (using a single strand to jump a diode)

Ernie

Lynx

Tim the voltage dip a peak detect charger uses to terminate the charge is on the way in so the diode is irrelevent. Can't you set up the triton to override those saftey precautions? If you know the capacity and number of cells in the pack you should be able to set it up to charge just fine, as long as you're not using the automatic pack detect, or trying to discharge

Tim_Indy

Okay, if you say so......again, I'm no expert.
This I do know something about. The first thing the Triton does is make sure a battery is in fact connected before it starts the charge cycle. It looks for voltage, and if the diode isn't jumped, it doesn't see any voltage, so it doesn't start the charge cycle. My Super Nova did the same thing. Knowing the capacity, number of cells, etc. won't help if the charger thinks there is no battery connected. Jumping the diode provides verification there IS a battery connected, since the charger has no problem "talking" to the battery. Simple solution, and yields a reliable charge.

Ernie Misner

...............Tim the voltage dip a peak detect charger uses to terminate the charge is on the way in so the diode is irrelevent...............

Lynx, I'm no expert either, but I think there is something to this more than meets the eye here since both Sirius and Model Rectifier Corp. insist that no peak charger can work properly without feedBACK from the battery to detect the peak.

I don't see how there could be any feedback during a continuous charge cycle though without taking a pause though unless it is a pulse charger. Perhaps taking a "break" when nearing the peak?

Ernie

causeitflies

The key word here is "PROPERLY". Thus the "stupid" chargers work but "smart" charger companies claim theirs work better because they more accurately detect the peak via voltage feedback.

Lynx

The voltage drop on the battery will show up as a current fluctuation so the outgoing power itself can be used as feedback. Not to say any peak chargers do it this way but it can be done. Anyways if it doesn't work it doesn't work.

causeitflies

And is the voltage drop caused buy the slight overcharge? I think this how "older" peak detection works.

Ernie Misner

I do believe this to be true. MRC, who make the Super Brain charger, use a patented "micro peak detection" and they told me personally in an email that their charger would not work properly through a diode and needed feedback from the battery.

Ernie

Lynx

causeitflies. The voltage dip is the results of the saturation of the battery chemical with electrons, so the moment of the peak is the actual point at which the battery is full. Because of the way battery chemistry works though a follow up ultra low (c/20 c/30) trickle charge will further saturate the battery. It's like filling up a cup of water fast, once it starts overflowing if you stop the actual level will be a little bit lower than the edge of the cup because of all the water sloshing around due to the high current. If you let just a little bit of water flow at the end you'll fill the cup all the way up till you actually have a slight mound over the top of it (which is akin to the high voltage fully charged packs have)

causeitflies

Lynx, good analogy. That is what I'm saying about the old chargers. The overcharge causes the fluctuation in the ingoing current which is detected as the peak but it is actually after the peak. I don't know if this is the Delta scheme or what but this is why the diode makes no difference to them...I think