How critical is the buck/boost transition on icharger 308 Duo?

[rcflyersd]

I am running an icharger 308 Duo from a pair of DPS 600 server power supplies out putting right at 25 volts. I have read about the buck/boost transition that occurs as output voltage to a 6s pack nears input voltage of the charger. Is this condition detrimental to the charger or should I bump up output voltage of the power supplies. I found that 550 ohm resistors between pins 3 & 9 of the PSU's gives output of around 26.4 volts (13.2 each) or should I leave the voltage as is?

[RedOctobyr]

My DPS-600PB supplies would shut down under a load when I had them at 13.25V each. I lowered them to 12.7V, and they would then keep going up to 45A output (as high as I pushed them).

All chargers will cross buck/boost when charging 6S off a 24V supply. If this was going to damage the charger, I'd be very surprised (since it's pretty much a given).

It can be tougher on your generator, if using one, as the load on the generator will fluctuate. The generator may start surging.

I have seen suggestions to drop the PS voltage to 12V each, to try and stay *under* buck/boost, rather than trying to climb above it. Server supplies will only go so high, as they're meant for 12V output.

[Gregor99]

Most power supplies cannot be turned up high enough to stay out of the transitions under load. That is the reason turning them down is what I recommend. Or for those that are up for a little experimenting, try it either way and see how it turns out. Use the graphical logging on the charger. Its a good exercise and can be very instructive.

To my knowledge iCharger has not commented as to if its bad for the chargers. I do know that Revolectrix has definitely commented that its not at all an issue for the charger. The affected components where considerably oversized.

What's more of an issue is when you are running from a generator. The pulsing causes instability in the AC source which makes its way back to the supplies and the charger. Instability in the DC can be harmful to the charger. This will be less of an issue running from AC.

[rcflyersd]

This past weekend, the wind actually went down enough to get out to the flying field.
So I was able to take out the 600 and 700 size machines after the long cold winter, and was able
to test out the DPS 600 pair with the 308 Duo under load powered by Honda EU2000i. What I ended up
with is 26.4 volts at the input of the 308Duo using 550 ohm resistors on each of the PSU's pins 3&9
Giving me 13.2 volts each. Using parallel charge boards I was able to charge 4 5000mah 6s (2 on each
side of the charger at 2C rate or 20 amps per channel) with no sign of buck/boost surging through out the charge cycle. So I believe I'm set to go with this setup for now.
I realize that with a set wattage output from the PSU's, if you increase the voltage output, you have to give
up some amperage capacity.
Normally I usually only charge at 1C rate anyway as I have multiple packs for each model and I usually
take at least 2 or 3 helis with for an outing just to "mix it up a little"

[RedOctobyr]

Impressive! When I had my DPS-600PB's at 13.25V each, they were cutting out (shutting themselves down) at something like 25A. Much lower than the 47A (even if you assume the higher voltage would mean a lower max-current limit).

I had to drop mine back down, I think I got them as low as 12.7V (adjusting the potentiometers I'd added for voltage adjustments as far as I could), and now I can do 47A.

That's great if yours are behaving better than mine.

[Gregor99]

Originally Posted by RedOctobyr

When I had my DPS-600PB's at 13.25V each,

I believe I was able to get a little more out of one of my sets of DPS-600PB's. But it didn't matter. Once they were loaded up to 40 amps the voltage dropped down close enough so the buck boost transitions occurred near the end of the charge cycle.

BTW, when tuning for BBT, I use the charge cycle logging as its much more precise and clear than listening to the generator.

[rcflyersd]

I'll try voltage logging function next time out (of course, it's snowing again here :-( ....) to see if buck/boost
transition occurs. My Honda gen didn't seem to have issue with it. It was cool out when I tried it last time and
possibly the PSU's may not put out the higher currents at higher ambient temperatures???

[Gregor99]

The issue is most clearly seen in the input and output current logs. It will not vary by ambient temperature. It will be affected by load. The load lowers the supply voltage which can move the BBT either earlier or later in the charge cycle. Or perhaps the load is high enough that charger states in boost mode the whole time. Or the load is light enough that the charger stays in buck mode the whole time.

The starting voltage also makes a difference. I had one set of supplies that always stayed in boost mode. I was pulling about 75% from the packs. Once I started pulling 80% from the packs, the voltage on the pack was low enough charge start out in buck mode and began the transitions right at the start of the charge cycle.