PL8 Pulse charging

[rossk]

I have noticed that when charging some packs the PL8's will pulse the charge rate.
Parallel charging 2x4400mah 7S packs from 20% on High Power @ 20A, the amps will drop down to about 15, then burst up to 26A, 5secs of 15A, then burst again up 26A for one second.
Seems to happen around 50-60% of the way through, then after about a minute of that it steadies back to 19.9A.
Im not sure how long it has been happening, but it was very noticable since it was the first time I was using a honda eu20i to charge in the field and it makes the generator rev up and down as the load is changing, so it prolly does it on mains power, but never noticed.
It didnt do it on all packs yesty, mainly just the 7S 4400 65C nano's.
I know I can turn the 'eco-throttle' on the gene off, to stop it from reving up and down, but that seems like a waste of fuel, since it will be running 100% then.

Setup:
Honda eu20i
Meanwell 2000watt
PL8 x 2
Nanotech 7S 4400mah 65C

[Gregor99]

Very common issue when the pack voltage is close to the input voltage. If it happens on 7s, you want to lower your power supply voltage to 25v. You may be able to get away with 26v. You'll need to experiment a little to find the right voltage.

[DominicD]

Originally Posted by Gregor99

Very common issue when the pack voltage is close to the input voltage. If it happens on 7s, you want to lower your power supply voltage to 25v. You may be able to get away with 26v. You'll need to experiment a little to find the right voltage.

Caused by switching from buck to boost and vice versa ?

[rossk]

Thanks, that does make sense, input voltage is currently set to 28.5V.
26V sounds pretty good, neither the 6S or 7S packs should be at 26v, so that should be the sweet spot.

[Gregor99]

Originally Posted by DominicD

Caused by switching from buck to boost and vice versa ?

Exactly. When the supply voltage is about 700mv above the pack voltage the DC-DC converter will toggle between buck and boost mode. Once the pack voltage clears the supply voltage, the DC-DC convert stays in boost mode.

[DominicD]

Originally Posted by Gregor99

Exactly. When the supply voltage is about 700mv above the pack voltage the DC-DC converter will toggle between buck and boost mode. Once the pack voltage clears the supply voltage, the DC-DC convert stays in boost mode.

I was partially paying attention in power electronics class ..... partially. Thanks for the explanation.

[Gregor99]

Originally Posted by rossk

Thanks, that does make sense, input voltage is currently set to 28.5V.
26V sounds pretty good, neither the 6S or 7S packs should be at 26v, so that should be the sweet spot.

The loaded supply voltage will need to be about 700mv above pack voltage. Loaded supply voltage can be seen in the supply graph in the CCS. 26v (loaded) will be fine for 6s. But for 7s, pack discharged down to 3.7v per cell is 25.9v.

[rossk]

Originally Posted by Gregor99

The loaded supply voltage will need to be about 700mv above pack voltage. Loaded supply voltage can be seen in the supply graph in the CCS. 26v (loaded) will be fine for 6s. But for 7s, pack discharged down to 3.7v per cell is 25.9v.

True, I was thinking that 3.7V was discharged fully, looked up my logs, looks like I landed @ 3.67, so 3.67 x 7 = 25.69.
I know I want to stay above 25.2, to avoid any issues with the top of 6S packs, so maybe 25.5 will be the go.

[apper001]

Does it harm anything when the Amp charge flutters for a while during charging 6S, Charger is 2x12.18=24.36V

have two dell nps 700-ab which i can only tweak to 2x12.9=25.8V or 2x11.3=22.6 + .7 =23.5V?

[rossk]

The biggest harm I have is that it makes the geni jump up and down while its happening.
I tried setting the psu to 25.5V, but that didn't work, jumps around during 24v on 6S, so I'm next going to try 26.5V, see how that goes.
Changing the psu voltage when it's all nice and neat in the case is a pita

[apper001]

don't have a generator and charge in the basement on 220V, so don't see it or hear the fans go up and down, just wondered if it harms the PS/charger/packs?

the Revo PS don't have this issue?

[rossk]

Originally Posted by apper001

the Revo PS don't have this issue?

It's got nothing to do with the psu or the source of the power.
It's the pl8 itself switching modes internally, causing it to draw more amps for short bursts.
I don't think it's really going to hurt anything

[DominicD]

Originally Posted by rossk

It's got nothing to do with the psu or the source of the power.
It's the pl8 itself switching modes internally, causing it to draw more amps for short bursts.
I don't think it's really going to hurt anything

But it does raise an interested question about PSU and generators. I've seen cases where this current pulsing cause some power supply and generator combinations problems.

[Gregor99]

FMA has commented that its not an issue for the charger and packs. Like Dominic says, it can be more of an issue for weaker power supplies and generators. For generators that have ECO mode, its helpful to disable this mode during the pulsing.

[DominicD]

Yup, I leave eco mode on when I charge the little stuff but you HAVE to run it full when pushing the higher wattage charges.

[apper001]

just lowered PS voltage to 23.7, charged four 6s packs on my two pl6 and no pulsing?

[Gregor99]

Originally Posted by apper001

just lowered PS voltage to 23.7, charged four 6s packs on my two pl6 and no pulsing?

Sounds about right. The loaded voltage will be pulled down out of the transition range. In some cases charging with too little current doesn't load the supply up enough and you still run into the issue.

BTW, the only way to see the loaded voltage is with the CCS on the supply voltage tab. The value on the console is more of an average voltage of the loaded and unloaded states that are occurring during charging.

[apper001]

Thanks for your answer, don't see yet why this couldn't be resolved in the firmware but maybe it's already planned for a future release

I thought i have checked both Console and CCS but haven't yet detected major differences on those values V/A for my PL6's.

[Gregor99]

Originally Posted by apper001

don't see yet why this couldn't be resolved in the firmware .

This is an issue with buck-boost DC-DC converted and all chargers, not just FMA. On smaller chargers, the transitions are often so light the user will not notice it. But I have seen logs from a 306b that clearly shows this is going on. Now its starting to become more common as 4010 guys with its larger power capabilities are running in to it and their current is jumping around, generators are pulsing etc.

Typically lowering the supply voltage will take care of it. Forward looking, higher supply voltages are the long term cure.

[spackermen]

Greg,

Is this also the switch from Cc to Cv charging? I'm not familiar with "buck" and "boost" is that the term for the power supply voltage has to be modified to match the battery voltage?