Johny's Electric Vogue

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Johny
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Post by Johny » Mon, 07 Jan 2013, 22:19

I have 12 switch mode chargers with no PFC.
I would like to improve the PFC. It doesn't have to be that great - but better would be good.
I have pondered a system to move 4 of the chargers phase in one direction and 4 in the other. The idea being to use an inductor in series with 4 of them to lag the phase and a big single phase run-type capacitor to lead another 4 chargers.
Anyone have any ideas. The chargers draw about 200W each - non-linear.

My alternative is to build (or buy) a PFC front end providing 340VDC for the whole lot (usually 360VDC but a bit of rippple would be OK). I don't really want to go down this path though.

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Post by Johny » Mon, 07 Jan 2013, 22:20

OH. The reason that I am considering this is that have a sneaky suspicion that my Smart Meter is over charging me by about 50%.

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Post by BigMouse » Tue, 08 Jan 2013, 03:40

If you don't want active PFC, and the charger's are always drawing roughly the same load, you shouldn't need to stagger them. If they're all lagging, then just caps on the input would correct them all at once. It's a pretty straight forward calculation if you know what the power factor and power consumption (either real or apparent) are now.

Energy meters are supposed to only charge you for real power. I'd be surprised if you're paying for your apparent power use.

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Post by antiscab » Tue, 08 Jan 2013, 03:47

BigMouse wrote:If they're all lagging, then just caps on the input would correct them all at once. It's a pretty straight forward calculation if you know what the power factor and power consumption (either real or apparent) are now.

Energy meters are supposed to only charge you for real power. I'd be surprised if you're paying for your apparent power use.


Load behind a rectifier bridge and caps (which is what these chargers are) have a poor PF, that is neither lagging nor leading (ie DPF is 1).

Energy meters (even official ones) won't read real power properly if the current spike (time wise) as the grid voltage rises above the cap voltage is too small (not enough measurement points)

forcing some of the chargers to be leading and others to be lagging will spread out the peaks, forcing the current drawn to be closer to the voltage waveform.

Personally I would just go for active PFC. That one from e-motor works couldn't be that much more expensive than buying caps and inductors...

You could also use it directly as a higher power charger.

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Post by coulomb » Tue, 08 Jan 2013, 14:04

Johny wrote: ... a big single phase run-type capacitor to lead another 4 chargers.
Anyone have any ideas. The chargers draw about 200W each - non-linear.

If you are thinking about a capacitor in series with the 4 supplies, I don't think it would work well. It would be effectively a short circuit for the sharp current spikes that the supplies will draw.

Also, drawing about an amp (~ 24R load), you'd want a capacitive reactance of around one ohm, to only lose about 4% of voltage across the capacitor. (This assuming sine wave current, which it isn't). That means it should be about 1/314th of a farad, or 3200 uF. This is quite a lot of 25 uF motor run capacitors. [ Edit: and that's per power supply that gets this treatment. ]

If you put them in parallel with the power supplies, then you are trying to power factor correct your whole house, and the effect of a few motor run capacitors would be negligible.

Besides, the phase of the power supply loads is actually quite good; the current that they draw is almost perfectly in phase with the peak of the mains. The problem is the distortion - they all draw around 10x the average load current for a tenth of each half cycle.

A simple filter (L or LC or LCL) will help with the distortion, and is probably the best solution. If you end up with a slightly lagging load, that's not so bad; there are plenty of lagging loads, and the peak current due to say a 0.8 sine wave power factor will be much less than the peak currents from 12 non-power-factor corrected power supplies.

I believe that if you have an LC or LCL load, you can adjust the value of the C to make the overall power factor close to unity (as far as phase is concerned; there would still be a lot of current ripple due to the rectifiers).

It's probably too late now, but the best solution would probably have been to pay a bit more up front for 12 power factor corrected power supplies; that would have avoided the heavy L and bulky L and C of the filters, and the resultant power factor would be about 98% (i.e. extremely good).
Last edited by coulomb on Tue, 08 Jan 2013, 03:05, edited 1 time in total.
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Post by Johny » Tue, 08 Jan 2013, 15:23

Thanks for the input everyone.
Oh well -so much for lead/lagging chargers.

Yes, in retrospect (actually even at the time) I would have preferred PFC chargers but I really like the idea of 12 separate chargers for the 12 subpacks and I could not get PFC chargers at only 180W. My problem now is that a PFC charger probably won't fit - space is tight.
I also did not wire the system for a single charger so it would require a big rethink. Since I want to get on with the driving part - it can wait. I'll keep a look out for 180W PFC chargers. The alternative is of course to just build a PFC front end for the whole lot. It could replace the charger sequencer I have in the boot now.

The idea of an LC filter is probably best for now. It doesn't have to be on the vehicle - it could just be used at home where 99% of charging will take place. Not sure how to calculate the LC size.

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Post by Richo » Tue, 08 Jan 2013, 20:55

Meanwell have the LED power supplies which are essentially CC/CV chargers.
The HLG-240-30 has PFC, adjustable CC and CV.
So the short answer is NO but the long answer is YES.
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Post by Johny » Tue, 08 Jan 2013, 21:42

Looking into it now three years later I find several chargers that claim PFC front ends with <96% distortion and the same size as the 180W ones I already have. Now to see if I can sell the 12 I have. I'll try to sell one of my spare on eBay and see how it goes.
This could be an easy answer.

(Edited 4th Feb 2013. It wasn't. The chargers I saw online turned out NOT to have PFC front ends. Just a copy and paste from their adds for larger chargers.)
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Post by antiscab » Sat, 12 Jan 2013, 20:51

Hi Johny,

I have a dead TC Charger 2000W with active PF correction.

The good news is the PFC front end is alive and well, putting out 390v.

I can find out how much shipping is if you are interested.

That would solve your PF problems rather cheaply.

cheers,
Matt
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Post by Johny » Mon, 14 Jan 2013, 14:57

antiscab wrote:I have a dead TC Charger 2000W with active PF correction.

The good news is the PFC front end is alive and well, putting out 390v.

I can find out how much shipping is if you are interested.

That would solve your PF problems rather cheaply.

cheers,
Matt
Thanks Matt. Thanks for the offer. Let me explore some options first. I don't really want to add anything else if I can avoid it. I'm looking at converting all the chargers to "valley fill" front ends at the moment.

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Post by Johny » Mon, 04 Feb 2013, 16:27

I converted one of my spare 58V 3A chargers to "valley fill" in an effort to get a better power factor.
The front end of my chargers has no Inrush protection. The mains feeds the rectifier which then feeds two of 220uF 200VDC electrolytics in series with 150K balancing resistors across each electro.

It was straight-forward to cut the track between the electros (actually it wasn't - it was doable after pulling out one electro because they had joined them on both sides of the PCB) and insert a diode, then add two more diodes to result in the following modified circuit (while at it I added an NTC thermister which I have shown as a 5 Ohm):
Image

The result (the normal rectifier/filter cap arrangements gave about 300VDC to 340 VDC output so 40V of ripple) was a LOT of ripple (understandably).
Simulation.
Image

So, could the switch mode part of the charger cope with this amount of ripple? Short answer - not really.
The charger worked fine and was quite stable but could only output 3A at up to 45 VDC then it dropped off to about 1.5A at 59 VDC - not enough. Actually it would work OK, the problem would be that I would not be able to easily predict charger power. I'm not prepared to modify them any further.

Interesting experiment though.
Last edited by Johny on Mon, 04 Feb 2013, 05:30, edited 1 time in total.

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Post by coulomb » Mon, 04 Feb 2013, 17:22

Johny wrote: Interesting experiment though.

Yes, thanks for sharing it.

As a point of interest, did you measure an improvement in power factor with one of the digital power meters that has a power factor reading?

As discussed in other threads here, they might not be trustworthy in this respect; especially the cheap ones don't seem to be able to deal properly with the large current spikes in the unmodified chargers. So depending on the meter, the results may or may not be meaningless.
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Post by Johny » Mon, 04 Feb 2013, 17:45

coulomb wrote:As a point of interest, did you measure an improvement in power factor with one of the digital power meters that has a power factor reading?
No I didn't. None of my stuff would be worth measuring it with. Instead I relied on documented info about valley fill which suggests 3rd harmonic dropping from around 86% to about 25% - ditto with 5th.

The next thing I was going to try was an inductor before the filter caps but simulations show cap voltage going over 400 V with no load so that's out.

So it's either:

1. Drop charge current to 2.5 Amps
2. Mains harmonic filer (quite hard to buy one)
3. 2.5kW active PFC front end
4. Live with it



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Post by celectric » Mon, 04 Feb 2013, 18:02

The schematic on the wiki page has a resistor in series with the centre diode, and a quick simulation suggests that this greatly improves the current waveform (better EMI). Doesn't help with the output voltage ripple though.

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Post by Johny » Mon, 04 Feb 2013, 18:15

celectric wrote: The schematic on the wiki page has a resistor in series with the centre diode, and a quick simulation suggests that this greatly improves the current waveform (better EMI). Doesn't help with the output voltage ripple though.
As you say the ripple gets worse. The resistor also is the better alternative to an inrush limiting system if you can handle the increased ripple. With heavy loads there is not much harmonic improvement with the resistor.

There is another type of valley fill that provides less ripple but requires more electros. I don't have the room in my chargers for this one.
It's essentially a voltage doubler.
Image

Output simulation:
Image

BTW. Valley fill passive PFC circuits are used in CFL lights apparently.
Last edited by Johny on Thu, 14 Feb 2013, 03:48, edited 1 time in total.

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Post by Renard » Tue, 05 Feb 2013, 02:46

Sincere congratulations on your engineer's approval. You must feel like a proud new parent, and as relieved as a new mother.
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Post by Johny » Tue, 05 Feb 2013, 14:40

Renard wrote: Sincere congratulations on your engineer's approval. You must feel like a proud new parent, and as relieved as a new mother.
Thanks Robert. It's now Vic Roads approved as well. Strangely It's an anti-climax. I expected some kind of argument or something (with Vic Roads). I totally forgot to ask about the $100 rego rebate so I guess I'll persue that for my fix.
The mother comment is pretty accurate I think.
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Post by woody » Tue, 05 Feb 2013, 19:29

Congrats Johny!
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Post by Johny » Tue, 05 Feb 2013, 19:34

Thanks Woody.
I still have a disturbing drive train vibration that the Vogue has when it was ICE powered. It starts around 50 km/h and is really bad at 90 km/h.

Considering that the motor, coupler and drive shaft are now all different (to the ICE), and they run true - I have to go looking at the differential. The flange runs true so I'm thinking diff pinion angle.
That's next - before I kill my motor bearings.

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Post by woody » Tue, 05 Feb 2013, 21:07

Wheel balance / flattened wheels due to standing too long?
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Post by Johny » Tue, 05 Feb 2013, 21:20

No, it's definitely drive shaft rate. A high speed vibration even at 50 km/h. It also is exactly the same on axle stands with rear wheels off.
Drive shaft has been back to manufacturer who says it's more than fine and motor and coupler alone are perfect (Edit: later I determined that they were not "perfect" at all). I measure a maximum of 10 thou runout in the drive shaft at the worst point now.

It even feels faster than normal drive shaft vibration which make me think driveshaft speed * 2 - making it a uni but unis are new and have good action.

The Vogue manual mentions taking care to place any axle shims back in the correct way around (shims between axle flange and leaf spring). We also know that the diff ratio is NOT what the car shipped with.
I am very suspicious of someone changing to whole rear axle. This also takes into account that I got two spare rear axles with the car...

Edit: fix typoes
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Post by Richo » Tue, 05 Feb 2013, 21:23

Bent axles
Worn wheel bearings
Loose/worn rear suspension
Not enough sub-woofers

Could get a $70 crash camera from office works and stick it to the underside and see if you can pin point the problem.
So the short answer is NO but the long answer is YES.
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Post by Johny » Tue, 05 Feb 2013, 21:32

Richo wrote:Could get a $70 crash camera from office works and stick it to the underside and see if you can pin point the problem.
It's DEFINITELY a drive shaft speed vibration - not axles - not wheels.

As I said - I can get it easily on axle stands so I don't need a camera.
I'll have to swap the drive config to a speed one for the axle stands because it's too hard to hold at 80km/h with torque control and bugger all friction.

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Post by cts_casemod » Thu, 14 Feb 2013, 11:23

Hi there,

Thought you guys could help me out. I finished my AC conversion, however I am having issues with the VFD loosing sync after releasing the throttle to brake. I then have to let a car get to a very low speed in order to sync again.

I was wondering what to use. I cant find much information on ac motors encoders and interface to the VFD. Couldnt I just use some hall sensors? If I need to use an encoder, can I use any type? And how do I set up the unit to read data from it?

Many Thanks

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Post by coulomb » Thu, 14 Feb 2013, 13:48

cts_casemod wrote: Couldnt I just use some hall sensors?
My guess is no. They all seem to want many pulses per revolution.
If I need to use an encoder, can I use any type? And how do I set up the unit to read data from it?

They're pretty standard, but you have to match voltages expected by the encoder interface and the encoder itself. Make sure you don't have too many pulses per rev, since there is usually a limit of some 65,000 pulses per rev at top speed.

You will almost certainly need a plug-in card specific to your VFD. If you don't have one already, it could be hard to find one. Their buses and plug-in form factors are all seem to be different, as far as I can tell.
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