Inverter won't run the microwave - Any ideas?

[Bushfamily5]

After weeks of reading, planning, re-planning and re-planning again I finished my inverter upgrade:

Installed two GC-2 6 volt batteries and ran 2/0 cabling (4ft in length to get into front cab of trailer) to a Xantrax Pro2000 inverter with a 200amp in-line fuse.
We simply plug our trailer into the inverter to run everything.

Well, we were out camping at the beach for the last week and a half and got to try everything out. Worked perfectly UNTIL i tried the microwave. Batteries read 12.0 amps, micro started for a milisecond and then the inverter beeped and micro shut down.

I thought the Pro2000 would be sufficient but maybe not? My Honda 2000 with 1600 watts running will do it.

Any ideas?

[wmtire]

What else were you using at the same time, since you stated the entire RV is running off the inverter?

Electrical usage and capability is additive. It's all about the total amps and/or watts.

[AudiDudi]

You are likely trying to draw in excess of 100amps from the batteries. If they were reading 12.0v (not amps), they were over 50% depleted already.

[richp]

Hi,


I have a Xantrex 2000 running on two T105s. It operates our microwave with no problem, as long as the state of charge is above 80% (or so) on my Trimetric meter and I don't have the refer or water heater running on electric.


FWIW.


Rich Phillips

[ScottBrownstein]

2000 should be fine. As others have indicated, what else is running. If you saw 12.0 volts when drawing from the microwave, that doesn't necessarily indicate that your batteries are low. I would put a voltmeter on the inverter input lugs and then try it. Perhaps you have a loose connection and at 100 amps it will drop your voltage a lot.

Do not try to run the microwave if your reefer or hot water heater is being run on AC. In addition, I assume that you have unplugged or flipped the breaker on your converter when you plug the coach into the inverter.

[Skyliner]

If no other unintentional loads on the inverter, your batteries,assuming full charge, are not able to handle the current draw and voltage drop hits point where inverter goes off line.

I have a 1500 watt Samlex inverter in my RV and it handles the microwave easily but I have 3 banks of EGC2 golf cart batteries online for my inverter.

[richp]

Hi,


To add a bit, when I was in Quartzsite this year, my microwave would kick out the inverter first thing in the morning if I had watched a lot of TV or movies via my Tivo the night before, and the battery state of charge was down in the 70s. A couple of hours of even low sun on my panels (600 watts) and I could use the microwave again. (My next system change will be more batteries to eliminate this.)



Just this past weekend we were in a Wisconsin campground with no electric and no generator use allowed. But aside from fans, we used relatively little electricity in the evening and overnite. So the batteries were in the high 80s in the morning, and the microwave was able to fire right up in the morning.


I agree with others -- if your batteries are indeed fully charged, start looking for other loads. But if you started the microwave with only 12.0 volts, you were way below what my experience suggests you need to power that kind of device.


Hope this helps.


Rich Phillips

[Bushfamily5]

All good input. Thank you

I think I may have messed it up then. When I went to inverter use, I did not turn the refrigerator to gas. Possibly that combined with the 50% batteries was the issue.

A couple times this weekend (because it is not habit yet) I left the converter on while using the inverter. May be one of those times.


Thank you all.

[bigred123]

if you are simply plugging your rv power cord into the inverter, isnt your converter trying to charge your batteries? I installed a 3 way selector switch with 4 poles so that I disconnect the charging circuit from the batttrey when on inverter.

[Larry-NC]

Originally Posted by ScottBrownstein

Do not try to run the microwave if your reefer or hot water heater or air conditioneris being run on AC. In addition, I assume that you have unplugged or flipped the breaker on your converter when you plug the coach into the inverter.

Larry

[camaraderie]

A 210Ah battery should be able to deliver right around 50 DC amps. The equivilent of FIVE AC amps...or about 600 watts (5x120 volts). My guess is both that your battery was pulled down and that it is not the size bank needed to run your micro...even if the inverter is.
You really should get a battery monitor installed rather than guess what it going on. See Victron or Trimetric.

[Bushfamily5]

I am using the digital display on the inverter as my battery monitor to give me the basic info I need: DC voltage of batteries as well as output power.

[camaraderie]

Originally Posted by Bushfamily5

I am using the digital display on the inverter as my battery monitor to give me the basic info I need: DC voltage of batteries as well as output power.

Voltage displays tell you nothing about the actual state of charge of a battery IN USE. They can only tell you when your batteries are dead and when they are being charged. Voltaage is only reliable to test state of charge with a DISCONNECTED battery that has been rested for 24 hours.
Wattage displays tell you nothing about the TOTAL draw on your batteries. You need to know:
ACTUAL state of charge.

AMPS of current being drawn

Amp hours REMAINING
TIME remaining at present use (i.e Peukert adjusted time remaining)

WHEN you've full charged the batteries and you can turn off the generator.

The actual amp load placed on your batteries by each often used item.

When your batts have hit 50% state of charge and need to be recharged.

If you are going off grid...you need a real battery monitor.

[richp]

Hi Bush,


As others have mentioned, you need a better monitor if inverter use is going to be a regular feature of your camping.


Another couple of other data points. When I used our microwave to reheat some pizza Friday night, my Trimetric meter showed it was drawing 115-120 amps for the two minutes it was operating. I inadvertently left my non led outside light on that night, drawing the battery down by a full 10 amps by itself over about 8 hours. A good monitor will help you more accurately gauge usage with information like this.



Hope this helps.


Rich Phillips

[dtptrson]

A microwave is rated by cooking power and not power consumption, so the typical 600 watt microwave is using 1100- 1200 watts. That's 110 to 120 dc amps. That's a lot to ask from a 2- 6 volt battery bank, even a brand new one. Using your microwave for for even 5 minutes will severely discharge your batteries. Trying to draw 100 amps is not the same as drawing 5 amps when it comes to discharge rate.
While you CAN do it, I'd plan on replacing your batteries often.
A 24 volts system would be the way to go for such high amps draws.

[richp]

Hi,


All the years I have been doing this solar thing, I have approached the power issue thusly.


My battery bank has about 100 usable amps, after the 50 percent rule is applied and various inefficiencies are taken into account. I can cumulatively draw 100 amps for an hour, through all devices -- inverted or not.



A two minute draw of 120 amps by my microwave is 1/30th of an hour -- pulling four amps out of that 100. As long as I stay within certain limits, I can use my microwave. At some point down the line, battery voltages will drop to where the inverter will disengage itself, leaving me use of my non inverted devices for a while longer.



Yes, that is sort of oversimplified, but is a functional day to day approach when you have a decent monitor.



FWIW.


Rich Phillips

[rk06382]

Originally Posted by Bushfamily5

All good input. Thank you

I think I may have messed it up then. When I went to inverter use, I did not turn the refrigerator to gas. Possibly that combined with the 50% batteries was the issue.

A couple times this weekend (because it is not habit yet) I left the converter on while using the inverter. May be one of those times.


Thank you all.

I just had a Samlex EVO-2212 Inverter/Charger installed. My 900 watt microwave consumes 1,500 watts.

With the Inverter Remote I was able to see:
1> The Fridge used 300 watts. Had to switch fridge to propane.
2> The AC has a heat-pump used 1,000 watts. Had to turn off AC circuit breaker to force furnace to use propane.
After the two above were on propane, I only saw a load of 12 watts.

I removed the Hot Water heater from the Circuit Panel. I plan to wire it to the shore power sub-panel later. The converter is disconnected as it is no longer needed.

I knew about the fridge but the heat pump was a surprise.

My install: Expanding compartment space for 2200 Watt Inverter/Charger

[dtptrson]

Originally Posted by richp

Hi,


All the years I have been doing this solar thing, I have approached the power issue thusly.


My battery bank has about 100 usable amps, after the 50 percent rule is applied and various inefficiencies are taken into account. I can cumulatively draw 100 amps for an hour, through all devices -- inverted or not.



A two minute draw of 120 amps by my microwave is 1/30th of an hour -- pulling four amps out of that 100. As long as I stay within certain limits, I can use my microwave. At some point down the line, battery voltages will drop to where the inverter will disengage itself, leaving me use of my non inverted devices for a while longer.



Yes, that is sort of oversimplified, but is a functional day to day approach when you have a decent monitor.



FWIW.


Rich Phillips

Unfortunately, it's not how batteries work.
DEEP CYCLE BATTERIES CHARGE RATE
Charge Rate, or C-rate, is a measure of how fast a battery is charged or discharged relative to its maximum capacity, or going from empty to full or full to empty. An empty 12 volt battery would be down to 10.5 volts (V). Likewise, a 6V battery is considered empty at 5.25V. Generally, when you see a battery listed at a certain amp-hour (Ah) capacity, it is usually at a 20 hour C-rate. This means it takes 20 hours to fill or empty the battery at that rate. For example, a 225 Ah (Amp-Hours) Trojan T-105-RE battery at a C-20 rate would be 225 amp-hours ÷ 20 hours = 11.25 amps (A).



Calculating C-20 Rate - Battery Charge Rate

The C-rate is important because the faster you charge or discharge a battery, the less energy it can store. Conversely, if you charge and discharge slowly, then it can actually store more energy than it is rated for. What this means is, if you have a battery that is rated at 225Ah at a C-20 rate (11.25A), but you have a bigger load drawing down your batteries faster than 11.25A, you will be operating at a different C-rate. You need to check the battery data sheet to see what the capacity will be at your load’s C-rate instead of C-20.



TROJAN T-105 RE 225Ah 6V Battery

C-Rate 2-Hr Rate 5-Hr Rate 10-Hr Rate 20-Hr Rate 48-Hr Rate 72-Hr Rate 100-Hr Rate
Amps 73A 37A 20.7A 11.25A 5A 3.4A 2.5A
Amp-hour 146Ah 185Ah 207Ah 225Ah 240Ah 245Ah 250Ah


Charge rate for Trojan T-105 RE

You can see in the example above for a Trojan T-105-RE 6V deep cycle battery, they rate the battery C-20 rate at 225Ah. That means if the battery has an 11.25 amp load, it will last for 20 hours before the battery is empty at 5.25V. If I increase my load, and draw at the C-10 rate of 20.7A, it can only store 207Ah, not 225Ah. So using more of the power faster, virtually shrinks the battery.

[Richard W Eason]

Periferal question: (Currently, I use only a small inverter for the TV). Bigred123 says, “I installed a 3 way selector switch with 4 poles so that I disconnect the charging circuit from the batttrey when on inverter.” Is there a way to automate that switch-over?

[mwdilday]

Are those batteries also powering your 12 volt systems on the trailer? If so are you powering the converter which is also trying to re-charge the batteries?