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Old 11-16-2022, 03:50 PM   #1
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Inverter not converting 12V to 120V to run microwave oven

Inverter not converting 12V to 120V to run microwave oven
Problem: Turned on inverter remote switch which showed input 13.5V and output showed one bar first and then the bar disappeared and no output was shown. Inverter appliance green light stayed on. Turned microwave oven on and it ran for 10 seconds with alert alarm and then it shut off. Reset inverter and waited 15 minutes and restarted with no good results. Question, why is there was no inverter output voltage when it was switched on. It was working before I modified the subpanel from 2 breakers to 4 breakers following forum member tdf-Texas’ expert posting. I also tested the GFCI with a lamp and it lighted up.
Assessment/Findings:
Simplex America SSW 1500 series, SSW-R1-12B remote switch, transfer switch and 2 breakers subpanel, single line outlet GFCI in the kitchen and microwave oven wiring were all factory installed.
Batteries voltage shown 13.5v using Fluke multimeter tester. Two Interstate 6V flood batteries, Extreme cycle GC2-ECL-UTL, RESERVE CAPACITY @25 Amp 225amp hour at 20 hours. Batteries is one and half years old supplied by Interstate battery dealer.
Microwave oven is a Dometic installed by ETI . Spec.: 120VAC 60 Hz 8.3A single phrase. Max. output is 700W and normal operation voltage is 40KV.
Gold power Solar charger showed 13.5 v output.
Requesting input and solutions to power the microwave oven using Inverter
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Old 11-16-2022, 04:53 PM   #2
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I don't have time to dig into this right now but Samlex has some pretty comprehensive troubleshooting guidance in their manual starting on page 20. Did you refer to that at all?
https://m.media-amazon.com/images/I/B1rPnx2aF8S.pdf
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Old 11-16-2022, 06:27 PM   #3
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Hello Rubicon 327,
Thanks for your response. Yes, I have a copy of the troubleshooting manual and had followed the instruction to reset and restart the inverter. I also called Samlex customer support and was informed that to operate the inverter, I must have a minimum battery reserve capacity of 200 amp which I don't quite understand because I have the RESERVE CAPACITY @25 Amp 225amp hour at 20 hours. Are they the same?

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Old 11-16-2022, 06:56 PM   #4
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...to operate the inverter, I must have a minimum battery reserve capacity of 200 amp which I don't quite understand because I have the RESERVE CAPACITY @25 Amp 225amp hour at 20 hours. Are they the same?
AGM or lead acid chemistry batteries have a higher internal resistance than Lion or LiFePo4 batteries. That means that your voltage drops much more under heavy load, and more heat is dissipated inside the batteries.

This is the kind of problem that might require a storage oscilloscope to positively diagnose.

However, I'm comfortable making the prediction that your inverter is shutting down because of under-voltage from the batteries, even if it's only for a brief surge.

If your microwave has different power settings, you might try starting out at a very low power setting and see what happens. Keep stepping up in power until you see the inverter go into fault again.
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Old 11-16-2022, 07:51 PM   #5
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I also called Samlex customer support and was informed that to operate the inverter, I must have a minimum battery reserve capacity of 200 amp which I don't quite understand because I have the RESERVE CAPACITY @25 Amp 225amp hour at 20 hours. Are they the same?
I agree it sounds like an under-voltage situation but dual 6V lead acid batteries that are fully charged should be plenty to run a small microwave from the inverter. This was the standard setup used by Escape for many years. That said the wires from the batteries to the inverter have been known to be undersized. What is the length of these wires and gauge? Was it working perfectly before you made wiring changes?
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Old 11-16-2022, 08:13 PM   #6
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Quote:
Originally Posted by SteveSgt View Post
AGM or lead acid chemistry batteries have a higher internal resistance than Lion or LiFePo4 batteries. That means that your voltage drops much more under heavy load, and more heat is dissipated inside the batteries.

This is the kind of problem that might require a storage oscilloscope to positively diagnose.

However, I'm comfortable making the prediction that your inverter is shutting down because of under-voltage from the batteries, even if it's only for a brief surge.

If your microwave has different power settings, you might try starting out at a very low power setting and see what happens. Keep stepping up in power until you see the inverter go into fault again.
Steve,
Thank you for your assessment that under-voltage from the batteries may be the problem. I kind of suspect that may be the problem. How do you solve that problem except to upgrade to higher voltage batteries?. My microwave oven does not have a powder setting. Would you please explain what is battery reserved capacity?. I can only find listing of 225 amp hour on my batteries. Can I assume that a higher voltage battery, eg. would be a 300 -400 amp hour?.

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Old 11-16-2022, 08:28 PM   #7
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Quote:
Originally Posted by rubicon327 View Post
I agree it sounds like an under-voltage situation but dual 6V lead acid batteries that are fully charged should be plenty to run a small microwave from the inverter. This was the standard setup used by Escape for many years. That said the wires from the batteries to the inverter have been known to be undersized. What is the length of these wires and gauge? Was it working perfectly before you made wiring changes?
rubicon327,
All set up and wiring are original. Batteries are stored in the exterior storage box and inverter located in the driver side dinette bench. I do not know the gauge and length of wire. Inverter was operating fine before I replaced the original batteries after 7 years. I suspected that the 2 new replacement batteries are lower voltage comparing with the originals. I did not make any wiring change except adding two breakers to the sub-panel to prevent breaker tripping when microwave oven was on and extra outlet was used.

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Old 11-16-2022, 08:30 PM   #8
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Steve,
Thank you for your assessment that under-voltage from the batteries may be the problem. I kind of suspect that may be the problem. How do you solve that problem except to upgrade to higher voltage batteries?. My microwave oven does not have a powder setting. Would you please explain what is battery reserved capacity?. I can only find listing of 225 amp hour on my batteries. Can I assume that a higher voltage battery, eg. would be a 300 -400 amp hour?.

Tonny LR
In our 2015 we have the RCA microwave provided by ETI. If yours is similar, there should be a power selection in the choices above the keypad. Enter the amount of cook time, hit power, then select any number from 1 (10%) to 9 (90%). Most of the small microwaves have 10 possible power settings. We had a similar issue a few months ago, 2 year old batteries, thought they were charged fully but the initial draw pulled them too low at start up. Also got a better monitor for the battery! Hope yours is an easy fix.
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Old 11-16-2022, 08:39 PM   #9
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In our 2015 we have the RCA microwave provided by ETI. If yours is similar, there should be a power selection in the choices above the keypad. Enter the amount of cook time, hit power, then select any number from 1 (10%) to 9 (90%). Most of the small microwaves have 10 possible power settings. We had a similar issue a few months ago, 2 year old batteries, thought they were charged fully but the initial draw pulled them too low at start up. Also got a better monitor for the battery! Hope yours is an easy fix.
Thanks. My microwave oven is a Dometic. when I use it, I select the timer and punch start. I will double check if there is a power selection.

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Old 11-16-2022, 08:47 PM   #10
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My microwave oven does not have a power setting. Would you please explain what is battery reserved capacity?
So my idea to assist you with troubleshooting won't work. During a power outage here I found out that I could run my 1,400W microwave on a 1,200W inverter and a 70Ah LiFePo4 battery by dialing the microwave's power down to 60%.

Anyway, to answer your question about battery capacity: This blog from Victron explains it very well, and saves me a LOT of typing:
www.victronenergy.com/blog/2015/03/30/batteries-lithium-ion-vs-agm/

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I can only find listing of 225 amp hour on my batteries. Can I assume that a higher voltage battery, eg. would be a 300 -400 amp hour.
I do know that AGM batteries are often rated at a C/20 load. That means if your battery has a 225_Ah capacity, they got that number by finding out that it lasted for 20 hours when driving an 11.25A load.

If your microwave is drawing 8.3A at 120VAC from your inverter, your inverter is drawing at least 83A from your battery, and perhaps over 100A at start-up. At that level of current, one needs to look at what the voltage drop is (because of inherent resistance) between the battery terminals and the inverter terminals. A larger gauge wire, a shorter wire, a better crimp or soldering job, tighter bolts on the lugs, cleaner lugs, and other factors can make big differences when the current is that high.

One troubleshooting thing you can do would be to run some other static load, like a space heater, hot plate, or blow drier with a known wattage at or below the power of your microwave, and measure the voltage drop between your inverter and your battery. Make sure you make that measurement on both the positive and negative wire. (I.e. connect one probe of your volt meter to the battery terminal, and one to the inverter terminal.)

If that voltage is less than 0.1V, then your inverter to battery wiring is not the problem. If it's close to 1V or more, you've got (dangerously) excessive resistance between the battery and the inverter.

Also, use your own separate volt meter to measure how much your battery voltage drops on a similar static load. That could indicate a failing battery.
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Old 11-16-2022, 08:56 PM   #11
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We had a similar issue a few months ago, 2 year old batteries, thought they were charged fully but the initial draw pulled them too low at start up. Also got a better monitor for the battery! Hope yours is an easy fix.
I also fear Tonny LR's problem could be aged batteries. But for their cost, I certainly would investigate every other possibility first.
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Old 11-16-2022, 11:09 PM   #12
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I also fear Tonny LR's problem could be aged batteries. But for their cost, I certainly would investigate every other possibility first.
Start with the easy ones first. In addition to checking the voltage drop between the battery terminal and the inverter terminal, do this: With a friend, put your meter probes directly on the + & - inverter terminals. Have the friend turn on the microwave (or better, one of the alternate, smaller loads like a hair dryer on low, space heater on low, etc). With a careful eye, capture the lowest reading on your meter - usually right at startup. Let us know what you find.
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Old 11-16-2022, 11:12 PM   #13
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I also fear Tonny LR's problem could be aged batteries. But for their cost, I certainly would investigate every other possibility first.
Original post indicates they are only 1.5 years old
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Old 11-16-2022, 11:40 PM   #14
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Original post indicates they are only 1.5 years old
I noticed that. But batteries age by cycles as much or more than by time. And lead/acid (including AGM) age by depth of discharge and by heat (higher charge/discharge currents age them faster).
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Old 11-17-2022, 08:58 AM   #15
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So my idea to assist you with troubleshooting won't work. During a power outage here I found out that I could run my 1,400W microwave on a 1,200W inverter and a 70Ah LiFePo4 battery by dialing the microwave's power down to 60%.

Anyway, to answer your question about battery capacity: This blog from Victron explains it very well, and saves me a LOT of typing:
www.victronenergy.com/blog/2015/03/30/batteries-lithium-ion-vs-agm/



I do know that AGM batteries are often rated at a C/20 load. That means if your battery has a 225_Ah capacity, they got that number by finding out that it lasted for 20 hours when driving an 11.25A load.

If your microwave is drawing 8.3A at 120VAC from your inverter, your inverter is drawing at least 83A from your battery, and perhaps over 100A at start-up. At that level of current, one needs to look at what the voltage drop is (because of inherent resistance) between the battery terminals and the inverter terminals. A larger gauge wire, a shorter wire, a better crimp or soldering job, tighter bolts on the lugs, cleaner lugs, and other factors can make big differences when the current is that high.

One troubleshooting thing you can do would be to run some other static load, like a space heater, hot plate, or blow drier with a known wattage at or below the power of your microwave, and measure the voltage drop between your inverter and your battery. Make sure you make that measurement on both the positive and negative wire. (I.e. connect one probe of your volt meter to the battery terminal, and one to the inverter terminal.)

If that voltage is less than 0.1V, then your inverter to battery wiring is not the problem. If it's close to 1V or more, you've got (dangerously) excessive resistance between the battery and the inverter.

Also, use your own separate volt meter to measure how much your battery voltage drops on a similar static load. That could indicate a failing battery.
Thank you for all the info and suggestions. I will conduct the blow drier with a known wattage at or below the power of my microwave this PM when outdoor temperature is warmer. Will also recheck and tighten connections.
According to owner's manual troubleshooting page, when the converter is functioning properly it should show input voltage which is 13.5V and output voltage which should be several bars on the remote display screen. In this case there was no output bars shown.
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Old 11-17-2022, 09:02 AM   #16
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Hello alanmalk'
Thanks for your suggestions. I will follow your instructions this PM to do the test.

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Old 11-17-2022, 10:11 AM   #17
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I noticed that. But batteries age by cycles as much or more than by time.
...
I have read (meaning - I don't take responsibility for what I am about to say) - that most batteries are murdered by their owners than die of old age.

Yes, there are many factors that can kill a battery prematurely, but other factors, like corrosion and loose connections, can mimic the early signs of battery death. At least those are fixable.
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Old 11-17-2022, 01:41 PM   #18
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rubicon327,
All set up and wiring are original. Batteries are stored in the exterior storage box and inverter located in the driver side dinette bench. I do not know the gauge and length of wire. Inverter was operating fine before I replaced the original batteries after 7 years. I suspected that the 2 new replacement batteries are lower voltage comparing with the originals. I did not make any wiring change except adding two breakers to the sub-panel to prevent breaker tripping when microwave oven was on and extra outlet was used.
If it was working perfectly it shouldn't be the wiring then. I see it is pretty cold there in Little Rock. Is it possible that temperature is impacting your batteries since they are in the front storage box? Your Interstate GC2's as spec'd should not have a lower voltage than original. I would disconnect the batteries from all load and solar input and put your voltmeter across the pair and across them individually. With solar input you may have been reading what is being sent to the batteries and not it's actual charge. It's possible you could have a bad cell and the problem is only apparent when you put a large load on.
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Old 11-17-2022, 01:50 PM   #19
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If it was working perfectly it shouldn't be the wiring then.
I agree. (Unless it's at the battery terminals.)

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It's possible you could have a bad cell and the problem is only apparent when you put a large load on.
People I know who maintain backup solar power systems for public safety radio repeater (relay) sites have been telling me that the quality and reliability of all lead acid batteries has fallen in the past 3-4 years. Because of the chemistry and physics of such batteries, you wouldn't see such problems until you put them under significant load. Such sites are all converting to LiFePo4 batteries as soon as they can.

Late last year I had a battery replaced in a small car. The tech installed one new battery, tested it under load, and then took it out and put in another one. It tested OK.

He said almost one in five are sent back as warranty claims.
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Old 11-17-2022, 02:22 PM   #20
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... I also called Samlex customer support and was informed that to operate the inverter, I must have a minimum battery reserve capacity of 200 amp which I don't quite understand because I have the RESERVE CAPACITY @25 Amp 225amp hour at 20 hours. Are they the same?
"200 amp" is not a measure of reserve capacity. Whether the customer support person actually said that or they were misunderstood, a number of amps is not a reserve capacity.

"RESERVE CAPACITY @25 Amp 225amp hour at 20 hours" doesn't make any sense. It looks like a combination of two specifications:
  1. "RESERVE CAPACITY @25 Amp", which is a label missing the actual value, which should be in minutes
    • This is a rating which is normally applied only to automotive batteries; it means the length of time that the battery can provide a steady current of 25 amps.
    • ETI's usual supplier is Interstate; their website lists only "N/A" for Reserve Capacity for both of their GC2-size batteries, and for their deep-cycle batteries in general.
  2. "225amp hour at 20 hours", which is the charge capacity of the battery (and should be "225 amp-hours at 20 hours")
    • this is the capacity of the GC2-ECL-UTL model of battery sold by Interstate (ETI's usual supplier)
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