How Big a Gen to Run a Converter? Some Info.
EDIT: some of my earlier posts in this thread have the wrong idea. As more info came in later, things got less confusing--sort of! :)
---------------------
Another look at this topic. It is not a question post, but perhaps some comments with added info will come in.
Example- you have a 55 amp converter and are shopping for a generator and decide you want a Honda (eg), but which one will do the job?
Note-I found out the " converter industry" uses the word "efficiency" to include the PF factor, so we don't have to think of efficiency and PF as two different things to apply to this problem.
Converter efficiency is the same as the efficiency of a solar controller. Watts out vs watts in. Simple. :)
We can easily get the watts out figure by noting the DC amps out and the battery voltage, but measuring the AC watts in requires a meter most of us don't have. We don't need that if we know the efficiency. Just derive it from the efficiency and watts out.
Why do that? Because we need to know how many watts the generator has to supply to run the converter. Since the efficiency includes the converter's PF, we can say the generator's requirement is its specified continuous VA rating.
Now back to that 55 amp converter. You see it goes to eg, 14.8v so your max output would be 55a x 14.8v = 814 watts
The efficiency should be specified for that converter somewhere. We have been told on here in the past, that PDs are around 70%. PowerMax says their 55 is at 85% but their 75s and above are PF corrected to be at 93% or so. Check the specs for any brand and converter amps size you are looking at.
(Some info suggests the efficiency is actually much less for converters depending on how hard they are working. No idea, so let's use the specs we have.)
At 85%, and output 814w, then you need 100/85 x 814 = 958w input
At 70% you need 100/70 x 814 = 1,163w input
If only they would make a PF corrected 55, then 100/93 x 814 = 875w input.
Looking at Honda ratings, you have 900 for the "1000w" and 1600 for the "2000w"
So now you can decide. You need a "2000w" for your 55 amp converter. The "1000w" can't run it at full converter output.
People with this problem sometimes do a "work -around" by reducing the converter output voltage with the Charge Wizard until charging amps taper enough that they can raise the voltage so that output watts stays under the limit.
Wouldn't it be nice if they made a PF corrected 55amper, which would, at 875 input required, be under the 900 rating for input? So sad, too bad.
You can use this calculation the other way, where you already have the gen, but now want to know how big of a charger you can run with it before going shopping for a charger.
BTW, the PD 45 amper and "1000" story is:
100/70 x (45 x 14.4) = 926, still over 900. We know people do run their 45 ampers with a "1000" somehow, so there must be a little wiggle room somewhere. A PD that has 14.8 max instead of 14.4 might exceed that wiggle room? No idea!
If the 45's efficiency is 85% with 14.8v max, then output is 45 x 14.8 = 666w and that needs 100/85 x 666 = 783 well under the 900 limit for a "1000"
---------------------
Another look at this topic. It is not a question post, but perhaps some comments with added info will come in.
Example- you have a 55 amp converter and are shopping for a generator and decide you want a Honda (eg), but which one will do the job?
Note-I found out the " converter industry" uses the word "efficiency" to include the PF factor, so we don't have to think of efficiency and PF as two different things to apply to this problem.
Converter efficiency is the same as the efficiency of a solar controller. Watts out vs watts in. Simple. :)
We can easily get the watts out figure by noting the DC amps out and the battery voltage, but measuring the AC watts in requires a meter most of us don't have. We don't need that if we know the efficiency. Just derive it from the efficiency and watts out.
Why do that? Because we need to know how many watts the generator has to supply to run the converter. Since the efficiency includes the converter's PF, we can say the generator's requirement is its specified continuous VA rating.
Now back to that 55 amp converter. You see it goes to eg, 14.8v so your max output would be 55a x 14.8v = 814 watts
The efficiency should be specified for that converter somewhere. We have been told on here in the past, that PDs are around 70%. PowerMax says their 55 is at 85% but their 75s and above are PF corrected to be at 93% or so. Check the specs for any brand and converter amps size you are looking at.
(Some info suggests the efficiency is actually much less for converters depending on how hard they are working. No idea, so let's use the specs we have.)
At 85%, and output 814w, then you need 100/85 x 814 = 958w input
At 70% you need 100/70 x 814 = 1,163w input
If only they would make a PF corrected 55, then 100/93 x 814 = 875w input.
Looking at Honda ratings, you have 900 for the "1000w" and 1600 for the "2000w"
So now you can decide. You need a "2000w" for your 55 amp converter. The "1000w" can't run it at full converter output.
People with this problem sometimes do a "work -around" by reducing the converter output voltage with the Charge Wizard until charging amps taper enough that they can raise the voltage so that output watts stays under the limit.
Wouldn't it be nice if they made a PF corrected 55amper, which would, at 875 input required, be under the 900 rating for input? So sad, too bad.
You can use this calculation the other way, where you already have the gen, but now want to know how big of a charger you can run with it before going shopping for a charger.
BTW, the PD 45 amper and "1000" story is:
100/70 x (45 x 14.4) = 926, still over 900. We know people do run their 45 ampers with a "1000" somehow, so there must be a little wiggle room somewhere. A PD that has 14.8 max instead of 14.4 might exceed that wiggle room? No idea!
If the 45's efficiency is 85% with 14.8v max, then output is 45 x 14.8 = 666w and that needs 100/85 x 666 = 783 well under the 900 limit for a "1000"
