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Old Sep 12, 2010, 07:09 AM
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Melbourne, Australia
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Yes, I tried that first. The Mastech will acually reach 31.5 volts..., but no luck. I think I actually squeeked out a few more amps into the charger with the voltage at 24.
??? Do you mean more amps out of the charger? For any given power out of the charger you will get more amps into the charger at lower voltage. If the charger error appears at 22A input that's 528W input at 24V but 660W at 30V so you should get 25% more output power at 30V input at the same limiting input current.
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Old Sep 12, 2010, 07:17 AM
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United States, MI, Grand Rapids
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Originally Posted by kgfly View Post
??? Do you mean more amps out of the charger? For any given power out of the charger you will get more amps into the charger at lower voltage. If the charger error appears at 22A input that's 528W input at 24V but 660W at 30V so you should get 25% more output power at 30V input at the same limiting input current.
Haha, I'm doing a good job of creating confusion.

I meant to say that I could set the charge rate a few amps higher without generating the error if I lowered the PS voltage. In either event, the amps knob was set wide open.

Regardless of the nuances or settings, I should be able to crank up the Mastech and let the PL8 rip without breaking a sweat.
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Old Sep 12, 2010, 08:00 AM
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Originally Posted by kgfly View Post
??? Do you mean more amps out of the charger? For any given power out of the charger you will get more amps into the charger at lower voltage. If the charger error appears at 22A input that's 528W input at 24V but 660W at 30V so you should get 25% more output power at 30V input at the same limiting input current.
According to the PL8 power supply spreadsheet from FMA, I was under the impression that the PL8 does not benefit from any voltage > 24v.
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Old Sep 12, 2010, 10:07 AM
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Haralson County GA. USA
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I have had a theory for a while now that some of these Supply Unstable errors are due to the simple(?) fact that the PL8 ramps up the charge rate extremely fast.

Way back here

http://www.rcgroups.com/forums/showp...postcount=1140

a user noted the difference even between using the CCS and the PL8's controls to start a charge..
His error was
Quote:
'charge lead over current error'
but perhaps these errors are related.

Some of my testing has shown that if I use a single 12V /30A server power supply and set a 6S charge rate high enough to cause the charge rate to be limited due to supply limits that the PL8 fans surge off and on at the start of the charge which would seem to indicate that the power supply is in fact dropping below 10.5 volts even though the PL8's or CCS display does not indicate such.

If one uses the PL8 controls and starts the charge rate at a lower rate then bumps the rate up in steps the power supply will not see such a heavy load all at once.

Charles
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Old Sep 12, 2010, 10:39 AM
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I found that the PL8 was overshooting my 30 amp set charging rate at the beginning causing this error. However, the latest firmware update seems to have fixed the current overshoot.

http://www.rcgroups.com/forums/showp...postcount=1519

***VERSION 2.04 8-23-10*** Reduced Amps overshoot to prevent false trips.
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Old Sep 12, 2010, 11:12 AM
Southern Pride
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Haralson County GA. USA
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Ramp ups

Eagle Tree is not as fast as a scope but is best I have on hand.

Both chargers were being powered by 12V /30A IMB 235 server power supplies is series for 24V @30A.

Charles
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Old Sep 12, 2010, 12:14 PM
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United States, MI, Grand Rapids
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Originally Posted by everydayflyer View Post
Eagle Tree is not as fast as a scope but is best I have on hand.

Both chargers were being powered by 12V /30A IMB 235 server power supplies is series for 24V @30A.

Charles
Interesting! This confirms the very erratic amp readings I was seeing on the Mastech display...it was wild enough to catch my attention immediately. Volts on the display were constant at 24.
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Old Sep 12, 2010, 01:18 PM
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Haralson County GA. USA
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Just for comaprison,

CP 10 took approx. 1 min to ramp up to 10-11 amps.

This is an old one I ran long ago but shows what ramp up times use to be in years past. I well remember my TP1010C taking well over a minutre to reach 10A charge rate.

Perhaps chargers are getting in to big of a hurry to get the job done.

Charles
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Old Sep 12, 2010, 02:10 PM
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.
Does connecting a large 12V Pb battery in parallel with the power supply smooth out the spikes? I know its not a permanent solution . . .
.
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Old Sep 12, 2010, 02:29 PM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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If by spikes you mean short term voltage drops then simple answer is yes.

Please note that my graphs above are the chargers output not the power supplies.

Post here where a 12V PB was used in parallel with ps.

http://www.rcgroups.com/forums/showp...postcount=1575
Note that the power supply was in fact also a Pb charger and thus had over 12V out put.

Charles
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Old Sep 12, 2010, 04:00 PM
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United States, MI, Grand Rapids
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Mastech 3050EX Charge attempts

Here 4 attempts to charge a 6s A123 pack.

I used my EagleTree and it was connected between the Mastech 3050EX power supply and the PL8.

So, in this case "pack amps" and "pack volts" actually represent the current and voltage coming from the Mastech...

First three charges ended a few seconds after the ramp up ending in "Power Supply Unstable" error and the charge was automatically terminated.

First attempt - 25 amps charge rate - fail
Second attempt - 22 amps charge rate - fail
Thrid attempt - 20 amps charge rate - fail
Fourth attempt - 18 amps charge rate - success if you can call it that...

Hope this helps...
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Last edited by SpeedVision; Sep 12, 2010 at 04:27 PM.
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Old Sep 12, 2010, 05:38 PM
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Originally Posted by everydayflyer View Post
Eagle Tree is not as fast as a scope but is best I have on hand.

Both chargers were being powered by 12V /30A IMB 235 server power supplies is series for 24V @30A.

Charles
Well that does seem ridiculously fast current ramp up to me. In this application, adding a few seconds to the overall process time is neither here nor there. Pacing the current ramp-up so it goes from zero to set-point at say 1A/s would make the PL8 a much kinder and more tolerant load and possibly avoid these problems. It is also interesting to see how "noisy" the load is compared to the other 30A charger. Could you please post the PL8 current ramp plot at an expanded time scale so we can see the details between 110 and 140s? What was the ET sample rate (IIRC 5 sample/s is the max rate)?
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Old Sep 12, 2010, 05:53 PM
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Seattle
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Originally Posted by PeteB View Post
According to the PL8 power supply spreadsheet from FMA, I was under the impression that the PL8 does not benefit from any voltage > 24v.
I suppose that depends on how you define "benefit". I believe the PL8 requires at least 24v to deliver 1000 watts. Increasing input voltage may not increase output power, but it will reduce input amps which I would say is beneficial. Any time you can trade volts for amps (higher volts, lower amps) its easier on the components and often times more efficient.
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Old Sep 12, 2010, 06:03 PM
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Originally Posted by kgfly View Post
Well that does seem ridiculously fast current ramp up to me. In this application, adding a few seconds to the overall process time is neither here nor there. Pacing the current ramp-up so it goes from zero to set-point at say 1A/s would make the PL8 a much kinder and more tolerant load and possibly avoid these problems. It is also interesting to see how "noisy" the load is compared to the other 30A charger. Could you please post the PL8 current ramp plot at an expanded time scale so we can see the details between 110 and 140s? What was the ET sample rate (IIRC 5 sample/s is the max rate)?
Between 110 and 140? That's where the charger was "thinking".

Here you go! Sample rate is 4x per second. This is the first attempt at 25 amps charge rate.

Keep in mind that the charger thinks for about 45 seconds before it demands any current. When it does, this is the kind of ramp up you get. I don't know enough to say if this is reasonable or not. I don't think it would be an advantage to FMA if such a narrow range of PS's would work with thier charger...
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Old Sep 12, 2010, 06:08 PM
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Seattle
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Originally Posted by kgfly View Post
It is also interesting to see how "noisy" the load is compared to the other 30A charger.
Very interesting indeed. Although I don't think that is noise. It looks more like current fluctuations which may be intentional. It would be good to hear from FMA as to whether or not these current fluctuations are by design. It would also be interesting to see of the current fluctuations only happen at high charge rates. Watching the CCS charge current, I've never seen this. But I've never charged higher than 12 amps.
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