DIY battery pack, can the inverter and charger be used simultaneously?

[rajseth]

For an off grid application with a generator and no solar - I am putting together a 24V battery, being charged by a Honda EU2000i generator into AIMS 24V/37A charger, and power being extracted by a 24V/3000W pure sine inverter.
Average power usage is about 500-700W, with peak at 2000-2200W.

Will this work? more importantly, will the generator be able to charge the battery at a constant rate, while the inverter pulls off power as needed.
At times, the charger will be supplying all the power to the inverter, and some balance current will flow into the battery, while other times, all the charger's output will go directly to the inverter with the battery making up the difference.

 

[snoobler]

Based on the description in this manual:

https://www.aimscorp.net/documents/PICOGLF10w-60w%20071618.pdf

Section 2.1

While I don't believe it actually works the way you describe (charge at constant rate and pull power), you will be able to charge and use power simultaneously. Charging will be limited to the max allowed and/or to the surplus based on loads and input power.

 

[rajseth]

I am not using the inverter charger. That would not work, since the moment the unit sees the generator come online, it would transfer all load to the generator and also start charging off it. The generator would overload.
I am using a separate inverter and a separate charger. If the battery were not there, the charger/power supply would be directly powering the inverter.

 

[Bud Martin]

Never mind, I see OP reply.

 

[rajseth]

Well - I just ordered the charger and inverter. I will hook up a couple car batteries to fill in for the 24V battery bank and see how it works.

 

[deeuubee]

Charging your battery from the Honda 2000i will work, but it will take a while to charge.
Depending on the Ah of your battery bank.
If you are putting 37A in and drawing 29A out. You are only charging at 8A.
The 2000i is rated at 1600 watts. If you draw 2000-2200 watts you will probably trip the overload.
Why not just run the load off the generator.

 

[rajseth]

Charging your battery from the Honda 2000i will work, but it will take a while to charge.
Depending on the Ah of your battery bank.
If you are putting 37A in and drawing 29A out. You are only charging at 8A.
The 2000i is rated at 1600 watts. If you draw 2000-2200 watts you will probably trip the overload.
Why not just run the load off the generator.

My aims charger will only put out 37A @28 V. So appx 1000 watts. That’s less than my steady draw so I will accumulate battery juice incrementally. Then battery will catch surges. And will replenish fully when I have grid power reestablished

 

[time2roll]

Will this work? more importantly, will the generator be able to charge the battery at a constant rate, while the inverter pulls off power as needed.

Yes it will work. No issues.

 

[John Frum]

My aims charger will only put out 37A @28 V. So appx 1000 watts. That’s less than my steady draw so I will accumulate battery juice incrementally. Then battery will catch surges. And will replenish fully when I have grid power reestablished

Lifepo4 batteries like to be cycled.
Lead acid batteries like to be full.

If you have lifepo4 batteries you either want to have a charge regime that allows them to cycle or alternatively float them at 3.35 volts per cell or less.
I have a very similar setup to yours.
Each night at 00:00 my ac power timer toggles off/on and starts my charger in boost mode of 29 volts for 30 minutes then 12 hours at 27.2 volts and then 25.9 volts until the power cycle.

 

[rajseth]

Lifepo4 batteries like to be cycled.
Lead acid batteries like to be full.

If you have lifepo4 batteries you either want to have a charge regime that allows them to cycle or alternatively float them at 3.35 volts per cell or less.
I have a very similar setup to yours.
Each night at 00:00 my ac power timer toggles off/on and starts my charger in boost mode of 29 volts for 30 minutes then 12 hours at 27.2 volts and then 25.9 volts until the power cycle.

hmmmm - dunno how I could accomplish that, but lemme talk to Rube Goldberg and think of scenarios. I will likely program the BMS to float the cells to 3.5, and then terminate the charging cycle. These cells will last my lifetime and get willed on to progeny - so I am not really worried
Building 8s 271Ah, overkill 24V BMS, AimsPower 24V37A charger (Will's bench charger) and a 3000W puresine inverter.

 

[deeuubee]

I'm not an off-grid expert, so if someone has a better way, I'm all ears.
Can you explain a little better what you're trying to do?
Are you running this as normal 24/7 power or emergency back-up?
You said something about when grid power is re-established.

With that 24V battery and 700 Watt (29A) draw, you would get maybe 7 hours use down to 20% SOC.
At that point, if you hook up the generator/charger, you might see max 37A charging, but your still drawing 29A average.
Like I said, your only going to get maybe 8 amps charging which would take around 24 hrs. to charge from 20 to 80+%
You will never get to 100% without disconnecting the load.
In which case, you're basically running off the generator.
I would think doubling your battery bank with 2 BMS to 542Ah@12V would be a better set-up for standby power.
You could get a 120A+ charger and cut down on generator time.

Using car batteries to see if it works, will only show you how bad car batteries are for back-up
The discharge voltage is not as linear as Lithium and would be comparing apples to oranges.

 

[rajseth]

Can you explain a little better what you're trying to do?
Are you running this as normal 24/7 power or emergency back-up?
You said something about when grid power is re-established.
With that 24V battery and 700 Watt (29A) draw, you would get maybe 7 hours use down to 20% SOC.
At that point, if you hook up the generator/charger, you might see max 37A charging, but your still drawing 29A average.
Like I said, your only going to get maybe 8 amps charging which would take around 24 hrs. to charge from 20 to 80+%
You will never get to 100% without disconnecting the load.
In which case, you're basically running off the generator.
I would think doubling your battery bank with 2 BMS to 542Ah@12V would be a better set-up for standby power.
You could get a 120A+ charger and cut down on generator time.

Using car batteries to see if it works, will only show you how bad car batteries are for back-up
The discharge voltage is not as linear as Lithium and would be comparing apples to oranges.

This is a house UPS in an ON-grid situation (my typo in OP). Right now, when we lose power, I have to go out there and hook up both the generators, in parallel, and let them run. Most of the time, one generator would be enough, to run the heat and fridges, unless they kick in together, or if I use the kettle. Seems wasteful, especially since in extended outage, gasoline becomes a dear commodity.
With this 280Ah24V setup, I get about 7kWh useful - which should last 8-10 hours. IOW, I can stay in bed and wait for the winter storms to pass. If its not winter, double that since the heating pumps will be idle.

Then, I will fire up the generator, plug in the 24V37A Aims charger, and let it deliver charge. When the heat cycles off, most of the juice will go to charge. In all other situations, LifeUPS will buffer the load.

Charging max load will be 28.8Vx 37A @ 90% = 1200W, which one generator can deliver easily. The batteries will regain charge gradually.
When grid power is restored, the batteries will get charged fully.

PS: This is more of a thought experiment, fun project, etc. We don't really lose power that often. I am also making a milk crate LifeGenerator for occasional off-grid cabin use, and also for intermittent on-grid use where I need 1500W for 3 hours, but only have 1/4 of a 20amp circuit. Charger can deliver 14.4V@20amps, approx 300W net or 7.2kWh / day, and I will use 4.5kWh in the use window. Problem solved.
Love LiFe

 

[deeuubee]

Have you done an actual load audit?
Use a Kill-A-Watt meter to get an actual 24 hour usage reading.
Are you saying the 700 watts is including the heat and fridge?

Can you do what you originally asked about, sure, but it seems highly impractical and inefficient.

You're only going to get one night of use out of that battery.
It's only gonna charge back up to 50% until you need it for overnight again.
Now you're down to 3-4 hrs. before you have to start up the generator again.
So, you're basically back to running the generator to 24/7.

For the occasional power outage, you can buy a lot of gas with that $2000

For 15 years, I have used the same Honda 2000i for occasional outages lasting up to a week.
In "econo" mode it's 8 hours. Without solar, there's just no efficient alternative.

 

[rajseth]

Have you done an actual load audit?
Use a Kill-A-Watt meter to get an actual 24 hour usage reading.
Are you saying the 700 watts is including the heat and fridge?

Can you do what you originally asked about, sure, but it seems highly impractical and inefficient.

You're only going to get one night of use out of that battery.
It's only gonna charge back up to 50% until you need it for overnight again.
Now you're down to 3-4 hrs. before you have to start up the generator again.
So, you're basically back to running the generator to 24/7.

For the occasional power outage, you can buy a lot of gas with that $2000

For 15 years, I have used the same Honda 2000i for occasional outages lasting up to a week.
In "econo" mode it's 8 hours. Without solar, there's just no efficient alternative.

The end goals of this exercise are:
1- not have to go attach the generator right away - eg. middle of the night, especially if I do not notice the outage
2- For an extended outage, to have only one generator running, and to use the UPS to handle transient higher usage.
3- If going away in winter - UPS for freeze protection - till my buddy can come start the generator for me.
4- ancillary - can repair a defective generator DURING an outage without disrupting quasi-normal life.

2nd night I don't care about, since the Generator will already be running, and all I have to do is fuel it for the night. I expect to run one generator 24/7 for an outage.

I have had my pair of Honda 2000i for 16 yrs and have used them regularly. The parts that annoy me are
1- having to get up as soon as the power goes out (never happens on a 70dF day when I am up already )
2- having to set up the companion in parallel every time I need higher than 1500W continuous.
3- not having freeze protection if no one is home

I keep 20 gallons of Aviation gasoline - it keeps for 50 years - plenty to get through the next week long Sandy type event

A standby whole house generator would do the trick - but that's $15K installed - and then I have another machine that can break. This setup, DIY, will run me 10% of that - and will last my lifetime with few moving parts

 

[deeuubee]

Are you hooking the UPS up to a transfer switch? Is it a commercial unit or are you building it?
Fridge, heat, lights are usually on separate circuits. In my case, separate phases.
The 3000 Watt inverter is basically one 20 amp circuit.

Please don't be offended by my questions, I'm seriously curious.
Being rural myself, I have 3 - 1000 VA UPS with units doing basically the same thing for when powers out.
(Fridge, propane heat (fan), security system)
I've been out of town and lost power when it was -5 deg., since then, added the UPS's.
$1500 would be nice, but I think you're way underestimating that.

 

[rajseth]

Are you hooking the UPS up to a transfer switch? Is it a commercial unit or are you building it?

Electronic Transfer switch with load shedding 120V 30A

Fridge, heat, lights are usually on separate circuits. In my case, separate phases.
The 3000 Watt inverter is basically one 20 amp circuit.

Yes, but the transfer switch handles that - disconnects Utility and puts them all on one phase

Please don't be offended by my questions, I'm seriously curious.

no offense - more questions mean I examine it in more detail

Being rural myself, I have 3 - 1000 VA UPS with units doing basically the same thing for when powers out.
(Fridge, propane heat (fan), security system)
I've been out of town and lost power when it was -5 deg., since then, added the UPS's.
$1500 would be nice, but I think you're way underestimating that.

nope $1.7-1.8K it is, $900 LiFePO4 8x271Ah, $150 overkill BMS, $200 Aims Charger, $400 3000W continuous pure sine inverter. All components picked are the ones stress tested by @Will Prowse - I didn't go for the cheapest....

I was going to do it with Lead Acid, since I do not need cycles. But to deliver the peak current, and for 7kWh, LiFePO4 was waaaaay better and same $$$ - and the hassle of venting, size, weight etc.