Generator size for Megawatt PS?

I was being flip with the more the merrier quip.

Don't be surprised if you have to increase capacitance. Without using a scope it is trial and error.

The PS caps and large inductor induce quite a phase shift upon startup. Try the flicker test plugging the Mega into a 16-gauge drop light cord with a 50-watt bulb burning.

I am not at all familiar with Honda inverter generators. But they "shouldn't" be as snotty as a similar capacity standard generator with regard to LC response characteristics.

I think what the Run cap does is basically a power factor correction.

Being on the AC side of the charger, the cap can't store energy like it would in DC, but it can (providing reactance) sync the current & Voltage phases to reduce the power required from the generator for a given output of the power supply.

If this is the case, then the size of the cap does matter like the following link shows. (so I'm disagreeing with MexicoWanderer about "the more the merrier" comment)

http://www.allaboutcircuits.com/vol_2/chpt_11/4.html

I also think this should answer jrnymn7's question - if the PF can be corrected to ~1, then you should be able to run a bigger PS off of a given Gen than otherwise able. There's gotta be other losses that I'm not thinking of also, so real world trials would trump theory. :)

It would be interesting to try MexicoWanderer's light dimming experiment with a non PFC and a PFC power supply back to back - assuming the same wattage rating for each supply.

Perhaps the 50uF cap you used just happened to be a good size - have you tried with different values?

Either way, I think for my initial question, I'll be getting the 36A Megawatt, and if I end up with a generator that struggles, I'll start trying caps on it - with the previous link & a kill-a-watt, I should be able to size it right-ish.

Good discussion everyone, Thanks!!

Mex,

Will that only help with the initial inrush, or could enough run caps keep say a pfc 100a charger running on a 13.8a max gennie, like the eu2000i?

Thanks!

WITH the 36/41 amp Megawatt...

Power it up and the 120 vac lights DIM for a moment. On shore power and Mexican house wiring.

WITH 50uf of motor run capacitors. No dimming. Not even the faintest flicker.

The capacitors and inductor in the PS take a big bite inrush to power up. Enough to kill a marginally sized generator. The caps help reduce this.

Wire the caps parallel with the line before the switch that powers the power supply. The caps have to power up before power is sent to the power supply. Vendors like Surplus Center in Nebraska sell motor run caps cheaply. The more the merrier. 100uf is not "too much". Gang them, put plug and socket pigtail connections, wrap it all up in Gorilla Tape then start spraying the lump down with Varathane. Coat after coat. 14-gauge wire will do fine. Works like a champ for any high inrush load including motors, chargers.

I think Mex was trying to trick us into learning :E

MEXICOWANDERER wrote:
100 uf motor RUN capacitor

I think you copy and pasted a phase shift article between volts and Amps for AC current. At least that's what pops up on my screen when I click on the link.

One can certainly start a 39 amp megawatt at a lower voltage to not exceed the Honda 1000 output.

I would not set it below the battery voltage however when starting, though I assume the unit has low voltage protection, unlike my cheapowatt which would emit strange noises like a ticking and whining bomb, when battery voltage was higher than the chosen voltage.

My Meanwell can do 41 amps, and I when I do set it to 13.2v, and hook up a depleted battery at 12.2v, 41 amps do flow, for a few seconds before tapering.

When I crank it upto 14.7v on a rested ~12.2v battery, 41 amps will flow for close to an Hour before tapering begins.

It is quite interesting watching how many amps flow at different applied voltages. The cabling between battery and PSU should be nice and thick. I use a few feet of 8awg through 45 amp anderson powerpoles and get 0.25v drop between voltage at terminals and battery voltage, at 41 amps.

Since the Megawatt's iny voltage pot only has a 270 degree sweep from minimum to maximum voltage, one can take note of the desired end position when in the end of CV stage and the battery is taking few amps and voltage drop is not much of an issue.

Solar is great for mitigating draws, and top charging, but blasting the batteries with higher amps, which mine seem to enjoy, requires other charging sources.

Low and slow does not always cut it, despite the affinity for the word 'trickle' by the general public regarding battery charging.

Thanks Ninerbikes, I was hoping someone with real world experience would chime in.

Greenrvgreen, I had thought of that at one point too, but forgot. Thanks for the reminder. I like the idea of a better adjustment pot, so that would make it even easier.

If the time comes for me to buy a generator, I may just go solar & use the PS for home charging.

Thanks again for the help!

You can also cheat any inrush current by starting the MW at a V below that of the bank, and then adjust upwards until it is running at the desired acceptance rate. Downside is that you cannot get an accurate fix of the MW's voltage setting while your batts are at a high rate of acceptance--it will read at batt V.

Keep measuring the voltage at the posts and adjust up or down as needed. You don't want to float charge at 18V!