Charger/gen head efficiency?

[BioHazard]

There's a lot of talk around here about how inefficient car alternators can be, maybe 60% if you're lucky? At the same time 120VAC gen heads are around 80% efficient, right?

So, let's say I have a regular generator and I plug in a 120vac battery charger that claims 89% efficiency. Would that be 80% x 89% for a total of 71.2% efficiency, or, better than most alternators?

[mobile_bob]

for a 12 volt system that is pretty close

in most cases a good AC generator with a good charger plugged into it will outperform most car alternators

on the other hand if you are going to have to charge a 24 or 48 volt system i can exceed the efficiency of a generator>charger
efficiency by as much as 10 percentage points using the methods described in the white paper.

i gave up working on improving efficiency of an automotive alternator charging a 12volt  system when it appeared that i would be
either going with a 24 or 48volt system.

i think it is possible to have a 12 volt large frame truck alternator such as the 110-555jho stator rewound so that its efficiency could
be improved to near 75% for the specific operation at a fixed speed such as what we typically use.

fwiw
bob g

[Lloyd]

Hi Boys..

One thing about running a 120 charger off a  generator. There is also a hit on efficiency taken because of the lower peak voltages of the wave form as compared to the grid wave form.

I've seen some chargers/150 amp that when plugged into shore/grid that can at best produce a 130 amp charge, but when running on a gen can only produce about 80-90 amps charge.

This has been especially true when the 120 gen set is below 12kw.

Lloyd

[DanG]

because of the lower peak voltages of the wave form as compared to the grid wave form

^^Depends on the exact alternator model... and/or your local grid voltages!

US grid line voltage is kept between 114 and 126 volts (I've seen 128+ but we are only house on a streetlight circuit)

114VRMS /.707 or 161.2 peak volts.
120VRMS /.707 or 169.7 peak volts.
126VRMS /.707 or 178.2 peak volts.

My Trace/Xantrex manual explains a generator true peak voltage equivalent to line AC is essential to proper function of chargers & many lower quality generators will not make the grade.

In order their inverter/chargers to make their ratings they specify at least 164V peak AC input...

At 150V peak AC my trace 120A charger will output only 60A at 14V
A 170V peak input will allow the full 120A of charging current to flow.

A motor powered stick welders 120 output waveform may have problems just by the nature of it.

EDIT - a true RMS meter check of output, or digging up man'f specs would confirm any suspicions..

[Lloyd]

You got it Dan, this is true of all charger that use a switch mode powers supply design, there is also an additional hit do to harmonic distortion, which back feeds the neutral and generates heat in the transformer windings, and or gen windings.

Based on my experience, a well designed DC gen will out perform an AC Gen/Stand Alone 120 charger.

As Bob's white paper demonstrates.

My trace remote has a switch that reads and displays peak wave voltage...I have seen as high as 184 peak from the grid.



Lloyd

because of the lower peak voltages of the wave form as compared to the grid wave form

^^Depends on the exact alternator model... and/or your local grid voltages!

US grid line voltage is kept between 114 and 126 volts (I've seen 128+ but we are only house on a streetlight circuit)

114VRMS /.707 or 161.2 peak volts.
120VRMS /.707 or 169.7 peak volts.
126VRMS /.707 or 178.2 peak volts.

My Trace/Xantrex manual explains a generator true peak voltage equivalent to line AC is essential to proper function of chargers & many lower quality generators will not make the grade.

In order their inverter/chargers to make their ratings they specify at least 164V peak AC input...

At 150V peak AC my trace 120A charger will output only 60A at 14V
A 170V peak input will allow the full 120A of charging current to flow.

A motor powered stick welders 120 output waveform may have problems just by the nature of it.

EDIT - a true RMS meter check of output, or digging up man'f specs would confirm any suspicions..

[BioHazard]

As usual, plenty of good information that quickly goes over my head. 

To be more specific, do you think this charger would work with my 800w 2 stroke generator?
http://www.progressivedyn.com/prod_details/rv_conv/rv_converter_pd9245c_2.html
They claim 105-130VAC, 725 watts. Would I be able to use the whole 45A output? Maybe I would be better with an older magnetic model for use with a generator?

Thanks guys

[mobile_bob]

i don't believe you are going to get anywhere near 40amps from a charger driven by the little 800 watt generator
and you will definitely not get there with an older transformer type as their power factor is horrible and the efficiency
of the transformer is of secondary concern in the design.

both add up to a very poorly performing setup, i know because i have the same generator and have used it with my 10amp shumacher
charger, the generator has a hell of a time keeping up with the 10amp max charge rate of the charger.

at some point in the future i would like to mate a large frame alternator to the little two stroke motor, i think that it might make 50amps
intermittently and maybe do 40amps continuous charge.

bob g

[BioHazard]

Damnit, another plan out the window. What about with a 2500w generator, would that power the 45A charger?

FWIW, the generator will power an 800w heater at about 110v. I honestly have no idea why it wouldn't power a 725w charger? The biggest one I've tried is a 6 amp and it worked with some lights too...

I'm with Edison. I hate AC....

[Lloyd]

Bio...
Youl will get some charging amps, but in a very inefficient way.

As an example on my boat I have an older Trace inverter/charger the charger is 150amp, I also have one of those 2 cycle inverter/gens which I believe is 900 watt max 800watt continuous. I have on a couple of occasions used this to run my inverter/charger.

During bulk charge the max charge I was able to get was just shy of 20 amps at 14.5v or 282 watts against an 800 watt input...so that works out to about a 35% efficiency not very good. This does not include the losses inherent in the the prime move to alternator losses...so total efficiency is some where just below 20%...or put another way 80% loss beginning to end.

My guess is if you were to bypass the on-board inverter of your little gen, and then rectify the on-board alternator out-put, you would find a better charge source. I believe that these alts are PMA's so you will need to set-up a dump loader so you don't cook the battery.

Lloyd

Damnit, another plan out the window. What about with a 2500w generator, would that power the 45A charger?

FWIW, the generator will power an 800w heater at about 110v. I honestly have no idea why it wouldn't power a 725w charger? The biggest one I've tried is a 6 amp and it worked with some lights too...

I'm with Edison. I hate AC....

[Apogee]

Why not just rectify the output of the small generator and run it into a solar charge controller designed to handle ~130 volts DC?

I would think this would be the most efficient way to go and you'd get all of the enhanced battery charging options to boot.

Steve

[mobile_bob]

the output would have to be fed to a mppt controller rather than a more common pwm solar controller

the reason being the pwm controller is limited to the current capacity of the generator, in the case of the 800 watt generator
about 7amps max

the mppt controller can buck the voltage down and increase the amperage,  in theory it could do nearly 70amps

however the mppt controller is going to cost more than the generator, the rectifier, and all the other stuff needed to connect it all together
probably by a factor of 2 or more.

bob g

[BioHazard]

My guess is if you were to bypass the on-board inverter of your little gen, and then rectify the on-board alternator out-put, you would find a better charge source. I believe that these alts are PMA's so you will need to set-up a dump loader so you don't cook the battery.

Lloyd

Interesting. My generator is not an inverter type, just a standard 3600RPM 2 pole gen head. I have seen others like you talk about that use the same engine but are inverter type. This one I think uses the same engine/PMA as the inverter gen, but outputs 12v/55A:
http://www.yang-ke.com/cpshow.asp?proid=20080429204251

Somebody said the inverter version is putting ~250V variable into the inverter. The charger version must send that 250v to a different "magic box" for 12v charge control. Any idea where I could find a "magic box" like that?

I would just buy one of those damn things but I haven't found the for sale anywhere yet and the MFG won't respond to my questions....

[veggie]

These guys claim that charging with an automotive type alternator is more efficient than using an AC generator coupled to a charger.
I happen to disagree with them being that I have seen AC generators in the 90%+ effy. range and I have a smart battery charger in the 85% effy. range.
Could these guys be doing anything special? or are they just plain wrong ?

http://www.thesolar.biz/diesel_battery_chargers.htm

veggie

[mike90045]

Well, you can always compare "watts delivered" 
  Listeroid  - gen - charger - ampmeter - battery.
  Genie - ampmeter - battery.


Batteries need to be empty enough to take a charge, and I'd say charge for 20 minutes or so, to get the alternators really warmed up, and see if there is a droop off.   Anyone got all this stuff ??

[Lloyd]

These guys claim that charging with an automotive type alternator is more efficient than using an AC generator coupled to a charger.
I happen to disagree with them being that I have seen AC generators in the 90%+ effy. range and I have a smart battery charger in the 85% effy. range.

Hi Veg.

Your AC gen 90% eff. is fuel to out-put. & your smart charge is based on grid power with higher peak voltages in the wave.

As I said most gens 12 kw and under out-put a peak wave as low as 140, but I've never seen one exceed 160. Now the problem lies with the swmp charger design most of the power in comes between the Peak voltage and the  cross of the next wave, with very little power coming below this. So 140 peak against and average 169 peak is about a 20% loss on top of the original 85% eff. rating, but there is also an additional hit that I don't have the answer to which is caused by the lower voltage peak generating a higher amper in the swmp design that heats all the discreets and transformer winding, as well as the windings in the alt.

So yea if an auto alt is set up properly, to max eff.... then I believe it will make a better bat charger...I think that done right it can even compete with Grid/smart charger.

Lloyd