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Old 07-27-2013, 01:37 PM   #21 (permalink)
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Quote:
Originally Posted by spackermen View Post
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?
Its not related to the CC/CV stages. Inside the charger there is a high power device called a DC to DC converter (aka DC-DC converter). Its job is to either raise or lower the incoming voltage to match the required output voltage. The output voltage needs to be slightly higher than the pack voltage for the current to flow. The charger's controller precisely manages the DC-DC converter so the output voltage is just high enough to achieve the charge current set by the operator.

When the DC-DC converter is raising the voltage, its operating in boost mode. An example of this would be charging a 6s pack (about 25v) using a 12v power supply. Conversely when he charger is lowering the incoming voltage its operating in buck mode. An example is when you are charging a 3s pack (about 12.5v) with a 24v supply.

The issue occurs when the charge cycle starts in boost mode and finishes in buck mode. This happens with LiPos that are close in voltage to the input voltage. An example is a 6s pack and a 24v supply. A discharged 6s pack is 22v and charged pack is 25.v. Another example is a 3s pack and a 12v supply. A discharged 3s pack is about 11v. A fully charged 3s pack is 12.6v/

At the start of the charge cycle, the pack voltage is lower than the supply voltage. So the DC-DC converter must reduce the incoming voltage. Midway through the charge, the pack voltage rises to the point where its close to the incoming voltage. The DC-DC can not longer run in buck mode, or the charge current will drop. So it switches to boost mode, increasing incoming voltage. The resulting current is higher than the set current so the charger falls back to buck mode. This "hunting" continues until the pack voltage is high enough that the charger can stay in boost mode.

There is a sort of "deadband" where buck mode would produce output voltage that is too low and boost mode would produce voltage that is too high. During this time, the charger does two things (see example below). First, it lowers the charge current in an effort to stay in buck mode a little longer. Secondly, it periodically switches to boost mode to see if the resulting current is too high. As the DC-DC converter is switching back and forth, this is when the supply and generator pulsing occurs. Eventually the pack voltage is high enough that the DC-DC converter can remain in boost mode.

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Old 08-21-2013, 07:33 PM   #22 (permalink)
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So are transition issues mostly dependent on the amount of current, or it inherent regardless of the rate you're at? In other words, do the oscillations grow in amplitude (for lack of a better word) as current increases? If it does, where does the ripple end up affecting your electronics the most?

I remember on my older/crappier supplies I had this issue with a Honda 2000i and one of them ended up dying (it was probably on the fritz anyways). The supplies I have now are rock-solid and put out more than double what it takes to run my PL-8 and can't say I've noticed any issues since. I don't typically charge at break-neck rates/amps all the time, but when I had my Aurora flying I would really put the screws to it.
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Old 08-21-2013, 09:23 PM   #23 (permalink)
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Q) In other words, do the oscillations grow in amplitude (for lack of a better word) as current increases?
A) Yes. The more current you are drawing the larger the oscillations will be. But if a higher current means the pack charges faster that also means that the pack voltage will move faster through the b/b transition zone. The result is the duration of the pulsing will be shorter.

Q) If it does, where does the ripple end up affecting your electronics the most?
A) As mentioned the charger is designed to handle it. If the power supply is struggling, the charger may report an unstable power supply safety code, which can be cleared by restarting the charge. As whether or not large transitions would prematurely wear the generator, or power supply; to date there have been no reported supply or generator failures related to the B/B transitions and they have been going on for a long time.
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Old 08-22-2013, 05:57 AM   #24 (permalink)
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Default PL8 Pulse charging

An update, I finally found the sweet spot, 27.0V as displayed on the pl8.
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Old 08-22-2013, 11:33 AM   #25 (permalink)
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I think it's more dependent on the particular supplies you use. Most drop in voltage a little bit as they load up. Yours are probably staying above the 25.2V mark under load when they start out at 27V. I'm going to try and have mine clamped to 13.5V (27V) to avoid the situation altogether as well, but I think 12.6V is what I have them set to for now (25.2V paired) with no noticeable problems.
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Old 08-22-2013, 01:14 PM   #26 (permalink)
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Quote:
Originally Posted by skunkworx View Post
I think it's more dependent on the particular supplies you use. Most drop in voltage a little bit as they load up. Yours are probably staying above the 25.2V mark under load when they start out at 27V. I'm going to try and have mine clamped to 13.5V (27V) to avoid the situation altogether as well, but I think 12.6V is what I have them set to for now (25.2V paired) with no noticeable problems.
I've tested with multiple different supplies, same model as well as different models, DPS-600pb, Dell 550W, (model AA23300) Dell 700W (model NPS-700AB). At my peak I had 14 different server supplies on hand, not counting the Pb battery and smaller 100 and 200 watt supplies. As long as there's voltage overlap between the input and output the transitions occur. It will even happen when powered from a lead acid battery charging a 3s pack.

On the DPS-600pb I did attempt to raise the voltage to see if I clear the transition voltage range. At about 13.85v (per supply), the supplies would hit over voltage and shutdown as soon as there was a load. I had to drop down to 13.5v per supply to support full output on 6s (Powerlab8). When you account for loaded voltage being lower plus the supply voltage needing to be at least 800mv higher than the output voltage it was not enough. All it did was move the transitions to later in the charge cycle where the pack voltage is slightly higher.

Granted, for the sake of discovery, I went a little overboard. So keep that in mind and remember that "technically" this is not an issue that must be solved for most users. Its more of an optimization. If you are getting the charge times you are after and your generator is not pulsing, there may been no need to do anything.
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Old 08-22-2013, 01:22 PM   #27 (permalink)
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been fighting this forever and didnt know what it was. I run with my gen at 1500 watts and it shuts down all the time when this pulsing starts. Then sometimes it would run at 1800 watts without a hiccupp. Going to 36v input power should solve my issue and let me get more out of my generator, thanks for the info!
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Old 08-22-2013, 02:13 PM   #28 (permalink)
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Default Re: PL8 Pulse charging

BrainDrain, it kind of goes without saying, but please do not do that if you are using a 32V-max PowerLab

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Old 08-22-2013, 02:39 PM   #29 (permalink)
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BrainDrain, it kind of goes without saying, but please do not do that if you are using a 32V-max PowerLab

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Yeah, I saw that, someone is selling his two PL8's getting another 4010i in the near future
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Old 08-22-2013, 05:38 PM   #30 (permalink)
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Default PL8 Pulse charging

Quote:
Originally Posted by BrainDrain_dx View Post
Yeah, I saw that, someone is selling his two PL8's getting another 4010i in the near future
Dual power lab takes 48V, problem solved.
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Old 08-22-2013, 05:54 PM   #31 (permalink)
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Dual power lab takes 48V, problem solved.
AVAILABLE LATE SEPTEMBER, 2013 = Vaperware at this point.

I need moar electrons NOW damn it

plus I really can't give up the icharger screen. Single screen with almost all the info is just too powerful. I often wear out my fingers just trying to see what amps I am charging at then how good my balance is on the PL8.

icharger is cheaper, does more cells, higher balance rate, uses standard balance port right out of the charger and mine has been bullet proof.
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Old 08-22-2013, 10:57 PM   #32 (permalink)
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So would you say leaving it in boost mode the whole time would be the best solution if you can't hit the higher voltages to stay in buck mode? I'm just interested in what's healthiest for the supplies since the charger should be fine on its own.


BrainDrain: does the 4010 have the IR's listed on the charge screen or is it like the 208b/306b where you have to go to a separate menu to access it? Also, how does it do with balance quality? I've found that the PL-8 conditions my batteries a LOT better than any other charger I've ever used and the final voltages are a lot more accurate than what I ever got out of my 208b. The 306b is a little better, but not the best. They're both a lot better than a Hyperion charger somehow.
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Old 08-22-2013, 11:06 PM   #33 (permalink)
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So would you say leaving it in boost mode the whole time would be the best solution if you can't hit the higher voltages to stay in buck mode? I'm just interested in what's healthiest for the supplies since the charger should be fine on its own.
Correct. If you can't get the voltage high enough with the supplies, I would lower to so it stays in boost mode during the entire charge. Shouldn't take much, just a volt or two below what it currently is at. Lowering the voltage is not an issue for the Powerlab8 due to the 60 amp input current limit. But on the Powerlab6 it will start to eat into the total wattage due to the 40 amp current limit.
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Old 08-22-2013, 11:57 PM   #34 (permalink)
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Originally Posted by skunkworx View Post
BrainDrain: does the 4010 have the IR's listed on the charge screen or is it like the 208b/306b where you have to go to a separate menu to access it? Also, how does it do with balance quality? I've found that the PL-8 conditions my batteries a LOT better than any other charger I've ever used and the final voltages are a lot more accurate than what I ever got out of my 208b. The 306b is a little better, but not the best. They're both a lot better than a Hyperion charger somehow.
There are 3 pages to look at. Ir's are on page two, one button click and you can see the IR for up to 10 cells on one screen.

I just charged a set of batteries today. Started at 30 and 28 mv difference. Ended at 2 and 3mv difference. Balancing is great. It shows this mv difference on the main screen, no looking at cells and adding it up.

So much information!
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Old 08-23-2013, 12:03 AM   #35 (permalink)
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The then a new icharger comes out...
http://www.progressiverc.com/icharger-308duo.html
only 30v max input but should be a nice competitor to the pl8duo
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Old 08-25-2013, 08:49 AM   #36 (permalink)
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Default PL8 Pulse charging

Another update, tried charging @ 30A and at the end of a 6S charge it started pulsing.
So I guess with the larger load it was pulling down the loaded voltage further, when it went below 22A it went solid again.
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Old 08-25-2013, 12:23 PM   #37 (permalink)
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Quote:
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Another update, tried charging @ 30A and at the end of a 6S charge it started pulsing.
So I guess with the larger load it was pulling down the loaded voltage further, when it went below 22A it went solid again.
That's what I found as well. Increase the current and the load supply voltage drops down into the transition range.

I've also gone the other way. I had some supply with a lower output voltage and the transitions never occurred because the charger was always in boost mode. I increased my flight times which used more of the pack and lowered the pack voltage. The lower pack voltage means the charger had to start in buck mode before transitioning.

The nice thing about the Powerlab8 is the 60 input current limit. You can drop the input voltage to 23v and still have headroom on the input current. Many supplies base their current ratings on wattage. So lowering the supply may increase the supplies current capability.
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Old 09-05-2013, 12:03 AM   #38 (permalink)
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Now this explains my issues charging at the field! My genset would start pulsing and causing me fits trying to find the source of the hunting.

Thanks for the info, guys.
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Old 09-05-2013, 10:09 AM   #39 (permalink)
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Well I really didn't gain all that much going 36v.
I was charging two 7s at 15 amp and one 12s at 9 amp on 24v source
I am now charging two 7s at 14.5 amp and one 12s at 12 amp on 36v source and I still get shutdowns if I start them at the same time. If I staggar the start between batteries 7 minutes or so everything runs fine. Seems about 1600 watts is the limit for the eu2000i. I do feel better though as the generator no longer runs erratically because there is no more pulsing.

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Old 09-05-2013, 10:25 AM   #40 (permalink)
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would a couple of extra C's between the PS and Output not prevent this?
if the dc-dc converter needs to lower the output it fills the C and if needs to raise it it drains the C.

or even easier in the firmware as the charger can steer the input current and lower the input untill it's out of the transition phase?
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