Generator Output Amps to Charger

[BoroDave C]

Hello all,

New to the board and look forward to learning and adding any of my experiences/ knowledge. I'm relatively new to alternative off grid living but have quite an appetite for new and better ways of doing the "norm."

I've been trying to wrap my head around a couple of things lately and was hoping someone could shed some light.

If my generator puts out 33.3 amps at 120 volt and half that amperage for 240, what amperage is actually being sent to the battery charger and what is the formula to determine the maximum amount of amps being deliver into the battery bank?

This providing there are no inefficiencies, heat loss, wire loss, etc...

My system is as follows:

Lister generator 6 hp, 4k head, w/ two legs of 120v for 240 volt sent to a 5kva 240 - 120 volt transformer.

This is sent into a midnight solar e-panel with a modified magnum 3924 watt inverter/120 amp charger hanging on the front.

The battery bank is made up of 16 Trojan T-105's hooked up in 4 strings of 4 for a 24 volt bank.

Note: I have not discharged my batteries below maybe 75% so I have never seen the charger display read higher then 60 amps or so.

[bob g]

your asking a question that cannot be simply answered with any precision

how much amperage is being delivered to the charger? that will depend on how much load there is on the charger, for instance

if the charger is 120volt input

and you are putting out 30 volts and 20amps

take the 30volts x 20amps =600watts

600watts/120volts = 5amps

so in this example the quick and dirty answer is 5amps input at 120volts gives you 30volts at 20amps output, but

that is an idealized scheme and nothing in the real world comes out like that, there are problems starting with power factor on the AC side, inverter/charger efficiency, and other losses, so

the reality might be as much as 10amps at 120vac to get 30vdc at 20amps output, and if the power factor is really bad it might be worse.

might be easier for you to get some idea by just getting a moderately priced clampon meter and just do some checking, even a cheap one will give you better numbers than you are going to be able to calculate given all the variables and unknowns in the system.

as far as max into the battery bank, that is a moving target, as the battery bank charges its ability to take in power drops off, or rather your charger will taper back the amperage. here a meter would be most useful if you wanna know what is going into the batteries.

don't know if this answers your questions or not, but i tried

bob g

[random]

The charger will attempt to draw what it thinks it needs.  Your charger should have a maximum amperes setting so you can size it to your battery bank.  "Good" chargers only deliver the current that the batteries can accept (up to their max-amps setting) then monitor (and decrease) that amount as they increase voltage.

If you have a 24v battery bank and have the charger connected to the generator's 120v side, the amps drawn on the generator will be the amps your charger is delivering to the batteries divided by 5 (approximately, assuming no other loads) since it's all about watts.

The only way to find out how many amps your charger is delivering to the batteries is to have an ammeter on the battery bank.  If you have direct DC loads while you are charging you will have to take that current into account.  

The only way to find out exactly how many amps are being drawn from the generator if you have any loads active (either DC loads or generator-passthrough) is to have an ammeter on the generator output line.  There are clamp-on inductive ammeters available but they aren't cheap.

Guessing is swell and I've wasted a lot of time doing that, but when I want to understand what's going on I've learned to just measure it.

[muskeg]

 Hi Dave.....

  Do you have the ME RC controller on your Magnum inverter?

If not your machine is set up in it defult mode for breaker size etc. Check the manual. And is your unit "power factor corrected"?

 I have the Magnum 4024  pure sine wave. 120/240 volt model and the control...

  What I found charging using a 8hp deutz diesel and 3kw lima generator .

 Set for 28 volts  bulk battery charging ( forgot absorb time offhand  Approx 4hours)

  Max breaker set at 15 amps 240 volt

  Normal Max DC charging 60 amps . Any more makes the genset work too hard..

  Genset meter readings...   each "leg" shows 120 volts @ 10amps  = 1200 watts

  1200 watts x 2 for 240 volts = 2400 watts which is close to my watt meter

 DC charging  reading from the ME RC control

  60 amps x 28 volts (which what the charge max set for)= 1680 watts

 It does not seem to matter  much what % the batteries are at 60 amps is the max charge and the volts rise with the battery volts.

 DC 1680 watts / AC 2400 watts = 70 % efficency ?

 Burning about 1 litre per hour.

  These numbers are from my analog meters and are close to what the trimetric says.

  If my numbers seem out to lunch a bit let me know ...

 Muskeg

 

[BoroDave C]

Thanks Guys.

I think I had an issue with realizing the final voltage was of course reduced going into the bank therefore increasing the amperage. More a function of the charger and a little Ohm's law math.

On a similar note, I'm curious what my Mig welder will pull not knowing what reduction there is in voltage given my reluctance to hook a meter to business end.

5 total amperage settings, the max being 140. Would be nice to know before I send it on its highest setting through my system.

Thanks again.

Dave

[BoroDave C]

Muskeg,

I'm going to mess around with a meter and the settings on the ME RC control. I'll take note of the battery state before during and after I charge..fuel too.

Thats a nice inverter. I kinda wish I had gotten the Pure but didnt have the $ at the time. In hindsight with the cost of a used 5kva transformer and the shipping it wouldnt have been that much more. Next time maybe.

[BoroDave C]

Direct meter reading without charge or load overnight was 25.5v so fully charged.

Bulk charge kicked in for no more than 30 seconds and raced up to 76 amps at 29.5 volts. 2242 watts

Not sure what the generator meters were reading, its out of site and would need two people.

Dropped down to absorption charge to 34 amp and still 29.5v and dropped again for about 2 hours at 17a @ 29.7v. 505 watts.

It finally dropped into float charge 27.5v, 0amp.

My fuel use was next to nothing (maybe 1/2 gallon of biodiesel) even with a second battery charger topping 2 very old 6v Trojans, 10amp drill, and grinder off and on for 3 plus hrs.

Totally missed reading the AC side of things to determine efficiency when it started. Would that be the same as power factor? Mines rated at .90