Amp readings don’t agree

[atWar]

I am probably showing my ignorance here but this bothers me so I’ll chance it. System: growatt 3000 spf, overkill bms, 24v lifepo 8s, 9000watt backup genset.
The generator has a 30 amp outlet. I have the growatt set max charge to 50 amps which it shows on the display when the generator is running and the bms shows the current as 75-80 amps. What gives? Can I be getting 80 amps from a 30 amp outlet? Or do they all measure current in different ways? I only run the generator when there is no solar so no additional amperage there.

 

[rodrick]

As you inverter/charger converts 120 volts ac to 24 volts dc your amps will increase this is normal

 

[BentleyJ]

A 24V battery will charge at about 28V. So 28V x 80A is only 2,240W. If your generator output is 120V then its only pushing about 19A. If the generator Voltage is 240V then the amperage is 19/2 = 9.5A

The better question is why the current readings between the Growatt setting and the BMS vary so much.

 

[Steve_S]

I run a full 24V system. My charger is throttled to deliver 80A DV to Battery Pack @ 27.2V. The Samlex EVO is very efficient and it pulls 120V/23-25 Amps (floats a bit) and also provides Passthrough during charge. Remember you are stepping down from 120VAC to <30V DC. The Growatt should be seeing the Input AC Voltage & Amperage and also displaying the DC Voltage & Amperage going to battery.

 

[atWar]

A 24V battery will charge at about 28V. So 28V x 80A is only 2,240W. If your generator output is 120V then its only pushing about 19A. If the generator Voltage is 240V then the amperage is 19/2 = 9.5A

The better question is why the current readings between the Growatt setting and the BMS vary so much.

So how would I test the actual amperage from the growatt without frying my meter? Your answer also makes me wonder about this generator. Growatt says a backup generator must be 10000 watts. If it is only pushing 19 amps wouldn’t a 4500 watt model do the job?

 

[BentleyJ]

So how would I test the actual amperage from the growatt without frying my meter?

Clamp On Ammeter. Like this:

Klein Tools AC/DC Digital Clamp Meter, Auto-Ranging 400 Amp CL390 - The Home Depot

Klein Tools CL390 is an automatically ranging true root mean squared (TRMS) digital clamp meter. It measures AC/DC current and NCVT via the clamp, AC/DC voltage, DC microamps, resistance, continuity, frequency, capacitance, and diodes via test leads, and temperature via a thermocouple probe. It...

www.homedepot.com

Growatt says a backup generator must be 10000 watts. If it is only pushing 19 amps wouldn’t a 4500 watt model do the job?

Yes,

 

[atWar]

A 24V battery will charge at about 28V. So 28V x 80A is only 2,240W. If your generator output is 120V then its only pushing about 19A. If the generator Voltage is 240V then the amperage is 19/2 = 9.5A

The better question is why the current readings between the Growatt setting and the BMS vary so much.

I ran the generator this morning and (I just now checked the bms session values) it says the max session charge power was 2231 watts and 82.7 A. So, by your numbers it seems the bms is closer?

 

[atWar]

Clamp On Ammeter. Like this:

Klein Tools AC/DC Digital Clamp Meter, Auto-Ranging 400 Amp CL390 - The Home Depot

Klein Tools CL390 is an automatically ranging true root mean squared (TRMS) digital clamp meter. It measures AC/DC current and NCVT via the clamp, AC/DC voltage, DC microamps, resistance, continuity, frequency, capacitance, and diodes via test leads, and temperature via a thermocouple probe. It...

www.homedepot.com

Yes,

Ok. I have one of those somewhere. I’ll try that. I also have a 4500 watt generator so I’ll pull that in and try it as well. Would save a lot of gas if it works. Of course it will have to handle any additional load like an extra 1000 watts for the pump. Thanks for this

 

[atWar]

I run a full 24V system. My charger is throttled to deliver 80A DV to Battery Pack @ 27.2V. The Samlex EVO is very efficient and it pulls 120V/23-25 Amps (floats a bit) and also provides Passthrough during charge. Remember you are stepping down from 120VAC to <30V DC. The Growatt should be seeing the Input AC Voltage & Amperage and also displaying the DC Voltage & Amperage going to battery.

I’m going to test the amperage next time it runs with a meter but the growatt display reads 50A when charging.

 

[BentleyJ]

Ok. I have one of those somewhere. I’ll try that. I also have a 4500 watt generator so I’ll pull that in and try it as well. Would save a lot of gas if it works. Of course it will have to handle any additional load like an extra 1000 watts for the pump. Thanks for this

If charging uses 2,250W and the pump is 1,000W that is still under the 4500W max of the smaller generator BUT most pumps require quite a large surge to get them started. So this is the down side of using a small generator. You are then limited as to how much charging and load support power is available to be used simultaneously.

 

[Steve_S]

I’m going to test the amperage next time it runs with a meter but the growatt display reads 50A when charging.

That is more than likely the AMPS going to Battery, not what it is pulling from the Generator.
As I said, I pull 120V/23-25A (2760W - 3000W) from my genset to charge my 24V Bank @ 80A.
I use the Genset's L5:30 which is 30A Capable.
I am using an Champion 4650W Peak Inverter Generator. Avail with manual start, electric start & even Dual Fuel.

 

[atWar]

If charging uses 2,250W and the pump is 1,000W that is still under the 4500W max of the smaller generator BUT most pumps require quite a large surge to get them started. So this is the down side of using a small generator. You are then limited as to how much charging and load support power is available to be used simultaneously.

Right. Good point. The pump is a grundfos soft start but probably still has significant surge. Will look it up. Thanks again.

 

[atWar]

That is more than likely the AMPS going to Battery, not what it is pulling from the Generator.
As I said, I pull 120V/23-25A (2760W - 3000W) from my genset to charge my 24V Bank @ 80A.
I use the Genset's L5:30 which is 30A Capable.
I am using a Champion 4650W Peak Inverter Generator. Avail with manual start, electric start & even Dual Fuel.

Thanks. I’ll check out the Champion. I like the dual fuel idea.