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Old 07-26-2021, 06:15 PM   #1
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4000w Inverter Timeout

I recently installed on my new NOBO 16.6 a 4000w inverter and a 200AH LiPo battery, and when I run the A/C or microwave they work for about 4 minutes while the battery voltage on my solar display shows a rapid voltage drop into the 10s, then 3, and then all power goes out, including the 12V system. After 5 minutes it all works again. No breakers or fuses popped, no hot wires.

I took the concept of plugging the shore power into the inverter and turning off the converter breaker, except that instead I hard wired the inverter into the WFCO panel by splicing the shore power feed through a manual transfer switch that switches between shore or inverter and sends power into where only the shore went previously. It also breaks the converter positive wire behind the breaker when switched to inverter.

The cables from the battery to the inverter are 0 gauge on a 5’ run, so voltage drop shouldn’t be an issue but I haven’t measured it. I used 10 gauge from the inverter to the panel. The inverter doesn’t have a pass through so given that the 12V system goes down I think it has to be the battery or the panel. What did I miss?
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Old 07-26-2021, 06:54 PM   #2
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Do you have any idea how many amps your drawing from the battery running the AC?
If I run my microwave it’s about 175 amps. With my 400 amp hours of battery, keeping the drain at 50%. I can run about 30 min.
I am guessing you don’t have enough battery because most battery’s have a current limit. Look up your LiPo battery max amp draw.
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Old 07-26-2021, 06:59 PM   #3
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You may be exceeding the discharge rate of the single battery and it's internal BMS is shutting it down
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Old 07-26-2021, 07:15 PM   #4
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Thanks! You might be right. My battery says it has a 100 amp continuous discharge current and 280 permanent. I’m sure I’m over that. I guess I’ll have to figure out if 2 batteries would cut it but this helps a lot!
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Old 07-26-2021, 07:19 PM   #5
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not enough battery to power an AC unit for ANY length of time...

You need MORE battery power to pull amps like that... maybe double or triple that battery pack.

15 amps of power @ 120VAC to the AC unit is minimum 150 amps @ 12 VDC ( your Li battery gives a bit higher voltage than 12 VDC I know) PLUS about 3-4 amps the inverter consumes) from the battery(s), so your 200 Ahr battery theoretically should last about an hour before being drained, and that is with NO voltage drops ( power lost) in any of the wiring. There is a limit as to how much power you can draw from any battery for an extended amount of time.

jbflag21ds explained that amp draw limit in previous post...
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Old 07-26-2021, 08:20 PM   #6
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Makes sense. I figured the set up would get me some microwaving and maybe a touch of A/C but I missed the battery draw limit. As long as I get over that then I should be good for a weekender. Thanks for the help.
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Old 07-27-2021, 05:43 PM   #7
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Originally Posted by IsThatYouClaude View Post
Makes sense. I figured the set up would get me some microwaving and maybe a touch of A/C but I missed the battery draw limit. As long as I get over that then I should be good for a weekender. Thanks for the help.
As for "a touch of A/C, here are some "perfect world numbers" to consider.

A 100 amp hour LiFePo4 battery contains between 1.2 and 1.5 Kwh of energy

A 13,500 btu A/C unit consumes about 1.5 Kw while running(not counting starting current).

An Inverter can be about 90% efficient if it's a good one. This means that 1.2 to 1.5 Kwh stored energy is effectively only 1 to 1.3 Kwh.

If all was perfect one might be able to run an A/C unit for 45 minutes per 100 ah battery. Since the max draw will be over 100 amps, two batteries in parallel will be required. First thought might be "Oh Goody, I can run A/C for 90 minutes on two batteries."

Unfortunately that's only perfect world, same current demand all the time.
Reality is that the compressor needs almost twice as much current to start as it does to run. This cuts run time drastically.

On my setup the A/C draws about the same current into the inverter as my microwave. That's a consistent 125 amps. The microwave is consuming 2 amp hours for every minute it runs (as measured by my Victron battery monitor). This is a "real world" number.

You MIGHT get an hour out of two LiFePo4 batteries if fully charged, no other power draws, and if you rub your lucky rabbit's foot.

I just run my microwave when only needed for a few minutes and run A/C on generator. If I need the A/C, I need it for hours, not minutes.
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Old 07-27-2021, 06:24 PM   #8
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most any INVERTER has a built-in LBCO, which is a LOW BATTERY CUT OFF feature, where when it senses a certain low battery 'voltage' reading, such as 10.5, it will AUTOMATICALLY cut off the inverter. The idea is that you don't want your battery usage, by the Inverter, to accidentally and unintentionally take your battery(s) down so low that you can't even bring them back to life.
On some inverters, this LBCO setting is customizable, but on others it is simply a static setting you might never otherwise even know about.

I imagine you are pulling a LOT of amperage, and the Voltage, while substantial with your type of battery, will still be pulled down initially by the operation of the a/c unit, causing the cut out, at some point. While the voltage reading may be 'temporary', once the Inverter sees then that the Voltage is again above a certain limit, such as 12.5, the inverter will come back to life.
Generally, the LBCO does not 'suddenly' cut off the inverter when it reaches a certain Voltage reading, but probably after a continuous 30 seconds under that number.

In our Palazzo, with our Magnum 200w Inverter, I set the LBCO to about 11.5 most of the time, but if off-grid, and wanting to use the Microwave or Coffee Maker for more than a minute, I would temporarily change the setting to 9.0 volts, so that the operation of either of those large-draw appliances would not suddenly cut OFF the inverter - since then you must wait for the Inverter to 'see' at least those 12.5 volts before it comes back to life. That generally means waiting for your generator to then recharge the batteries - defeating the purpose of using the Inverter in the first place!
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Old 07-27-2021, 06:36 PM   #9
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Do you have AGM batteries? I wonder if Li would solve that problem since they’re not supposed to fall off as much while discharging.
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