I recently built a charging case that has a 12-volt switching PS in it. I have 3 chargers in the case (not to use at once necessarily, just for flexibility) and I want to make sure I did the math right as far as sizing the new Inverter Generator I purchased for field charging.

My assumptions are that if I were to draw the entire 25 Amps the PS is capable of pushing @ 13.8 volts, that would be 345 watts. My question is how does the Amperage the PS draws equate to the Amps the Inverter Generator can support (it can support up to 8 Amps @ 120 VAC).

Is it as simple as 120 Volts x 8 Amps = capable of up to 960 Watts? Is there anything in there I need to factor considering I am going from A/C to DC? I assume there is some overhead but probably not much for a switching PS, I just want to be sure I won't get out there and have the Amp draw be too high for the Inverter Generator (which if my math is correct is capable of supporting 2.75 times the max draw of the Power Supply).

Any help would be much appreciated...

Jack

I am not sure what an "Inverter Generator" is but I would say your maths is close enough. The generator can output 120V/8A = 960W and in this case, watts are watts AC or DC.

The power supply is rated for 13.8V/25A = 345W, allowing for 90% efficiency it needs approx 383W input, say 400W to be safe. So your generator has plenty of headroom to run your DC power supply.

Originally Posted by kgfly

I am not sure what an "Inverter Generator" is but I would say your maths is close enough. The generator can output 120V/8A = 960W and in this case, watts are watts AC or DC.

The power supply is rated for 13.8V/25A = 345W, allowing for 90% efficiency it needs approx 383W input, say 400W to be safe. So your generator has plenty of headroom to run your DC power supply.

Thanks kgfly, much appreicated!

BTW, Inverter Generators produce DC power and the 'Inverter' feature converts it to AC. By doing so, the engine speed is not fixed. It can be varied according to power requirements. There are three main advantages to an Inverter Generator. The power is clean < 2.5% distortion compared to < 5% for mains power. They can be quieter than normal AC generators and they typically use less fuel...

Jack

How's their Inverter compare to separate/individual Power Inverters?

And, what's the general opinion of running switching power supplies off Inverters?

Originally Posted by jrb

How's their Inverter compare to separate/individual Power Inverters?

And, what's the general opinion of running switching power supplies off Inverters?

Well, an inverter is an inverter, in this case it's an inverter and a generator in one. The reason to use one for what we do would be to provide cleaner power to our chargers. Folks that use computers in the field can also benefit as computer power supplies can be more finicky, there have been issues with computers run from regular A/C generators.

Personally I have 2 reasons why I purchased an Inverter Generator over the traditional design. First the noise level is important, these generators operate at normal conversation levels because they can throttle down and only provide what's required. Second is the clean power though I am pretty sure I could charge off most regular generators.

They are more expensive but I can't imagine it going over well at an electric-only event like SEFF (next week!) for folks to crank up the cheap (and loud) generators that most folks own for home use. So for that reason primarily, I decided to go quiet and at the same time benefit from power meant to run computer-type equipment.

As for running a PS from an inverter, unless the power is coming from a generator, I don't see the point. To convert the DC to AC back to DC again seems pointless plus there is no advantage gained from a power POV since watts are watts. In the end your just losing some available watts from the conversion process back and forth. If you have a 12-volt power source, why not just run your charger(s) from that?

Jack

The MasTech 5020 is my charger and runs off 120VAC.

No problem at my home field; when away from AC I plan to use a power Inverter off my idling Explorer.

The MasTech charges the A123-10S2P pack in my ECQ (electric converted 1/4 Cub) @ 20amps (36volts).

This is 1:1! Fly for 10 minutes and its recharged in 10 minutes!

So my need is for AC 1st.

My other planes use A123s too: 1/5 -- 5S2P & FreeStyle 6S.

Originally Posted by jrb

The MasTech 5020 is my charger and runs off 120VAC.

Ah, that explains it! I thought you wanted to use the PS to simply power a DC charger. That's a lot of Amps Batman!

Jack

Originally Posted by jrb

The MasTech 5020 is my charger and runs off 120VAC.

No problem at my home field; when away from AC I plan to use a power Inverter off my idling Explorer.

The MasTech charges the A123-10S2P pack in my ECQ (electric converted 1/4 Cub) @ 20amps (36volts).

This is 1:1! Fly for 10 minutes and its recharged in 10 minutes!

So my need is for AC 1st.

My other planes use A123s too: 1/5 -- 5S2P & FreeStyle 6S.

I will be looking for a "best" field generator for same use - as it stands -I am caught with lugging around 3 lead acid deep discharge types (22 lbs apiece of decent ones ) a friend lugs around 5 marine batts (60v)for his 16 cell setup (A123)

This is all getting to be a problem--if I want under 10 min charge times .

as it stands -I am caught with lugging around 3 lead acid deep discharge types (22 lbs apiece of decent ones )

Those are light weights. Mine weigh 64 pounds each and there are two of them.

Hense the reason for my sem-permanate battery carrier?


Charles

Originally Posted by richard hanson

This is all getting to be a problem--if I want under 10 min charge times .

Not a problem; but certainly some interesting posibilities!

Zip by 3s! A freind is doing a 12S plane as two 6s, zipping with two Pbs in series.

MasTech, of AC, Inverter, or generator. Another friend say just be done Jim, get a Honda geneartor.

Dapters N chargers. use my 1010C and or Dapter too.

Just buy a computer power supply for like $20. 250 watts is low for computers but is mega high levels for the chargers. The connectors for cdroms and hardrives are 12 dc volts. Yellow and a black is good.

Mine works great.

Originally Posted by munky99999

Just buy a computer power supply for like $20. 250 watts is low for computers but is mega high levels for the chargers. The connectors for cdroms and hardrives are 12 dc volts. Yellow and a black is good.

Mine works great.

You are missing the details. A Mastec charges at up to 50 volts and up to 20 amps. it requires 120 V AC. jrd is using such a Mastec to charge 10S A123 pack at 36 volts and 20 amps. that is 720 watts output.

Zip charging : well I Zip charge a 3S A123 at 25 to 30 amps. start and 20 amp. average from two 12v dep cycles in parallel.(250 Ah) and also run other chargers from them. My 3S A123 is charged at over 200 watts average.

Some are Zip charging 3S8P (24 cells) at over 50 amps. or approx. 550 watts.

FYI I often pull over a 50 amp. (600 watts) load from my deep cycles.


Charles

You are missing the details. A Mastec charges at up to 50 volts and up to 20 amps. it requires 120 V AC. jrd is using such a Mastec to charge 10S A123 pack at 36 volts and 20 amps. that is 720 watts output.

wow that's some serious power You can certainly get the same wattage from very high end computer power supplies. So obviously the amps are there. The voltage however would need to be doubled up or something.

You're going to pay something nasty for such a regulated power supply at those levels.

http://www.surplussales.com/PowerSupplies/PowerS-5.html

or

http://new.tanicpacks.com/index.php?cPath=76_53

Originally Posted by jfetter

Well, an inverter is an inverter, in this case it's an inverter and a generator in one. The reason to use one for what we do would be to provide cleaner power to our chargers. Folks that use computers in the field can also benefit as computer power supplies can be more finicky, there have been issues with computers run from regular A/C generators.

......meant to run computer-type equipment....

.......

Jack

I am not familiar with this generator inverter solution
have you a link to the one you bough or similar spec type

For the original question is there eneogh headroom on 1000wat output and 400 watts consumption the probable answer is most likely but conversion rates with generator power output and inverter losses can be as high as 25% losses or more...if the quality of the electronics components is low and they are under high load factors

I am using a run of the mill $50 inverter 12v to 110v / 220V to run my laptop with a car 12 volt solution with the car engine running with no ill affects from spikes etc
Inverter is 150 watts and laptop demands 100 watts at 220 volts as the laptops battery is broken

My experience of Generators is they are often over stating their specs and you typicaly find a ~1000w is only ~800watt in continuous load and ~1000watt is short time peak loads such as ~1000 hand drill machine making holes with rests in between

The cheaper crud made in China ~1000 watts generators can be as low as ~600watts continuous

Also my guess is that most run of the mill petrol generators will with direct plug in 110v chargers will work without smothers or inverters whatever if the generators automatic speed up system is overridden and the gas is jammed at full speed as its the surge load pick up time that causes the equipment the most problems running on low voltages
Ok that will make more noise
My preference if I was going that direction is to get a cheaper 2kw generator( some can be had for $500 new ) and run a long lead say 100feet to the place of charging
The bigger 2kw generator wont be so affected with 400 watts demands and it will run at lower quieter speeds but will be a bit heavier to lift and use a tad more fuel

A few simple cheap capacitors will make a fairly effective smother for those nervous of spikes for their chargers

Other solutions would be to run 110v battery chargers like 10 amp types direct onto normal deep cycle batteries and then use 12 volt type chargers to charge the model planes cells and the battery will act as a smoothing circuit
This would be my own preferred solution I will opt to use
Its lighter simpler and cheaper and can be used to run several zip chargers for A123 packs or similar solutions

Others might use the 1kw or 2Kw AC 110v generator's with computer power supplies which do 13.5 volts to the charging

I agree with your solution as being probably most secure but it sounds pricey what did you pay for it roughly

Others might prefer cheaper easier solutions so I outline them as possible alternatives

Ralf

Originally Posted by treehog

I am not familiar with this generator inverter solution
have you a link to the one you bough or similar spec type.

Ralf

Ralf,

Here is the link to the one I got, it was a toss up between the Honda and the Yamaha. There is another reason I got this one, portability. It weighs only 27 pounds dry, that's easy to haul around and get in and out of the SUV. The noise really sold it though, 52dB is normal conversation.

Yamaha EF1000ISC Inverter Generator

Jack