The tongue of the Rpod - R-pod Owners Forum

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offgrid

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Joined: 23 Jul 2018
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Posts: 5290

Topic: The tongue of the Rpod
Posted: 14 Oct 2018 at 6:09pm

Its not the size of the inverter that effects the load on the batteries, iIs the size of the load and how long you run it. Energy = power x time. If you're only running the micro a few minutes a day which is pretty typical then its not adding much to your battery requirements. I run mine maybe 6 minutes a day so 1400 watts X 6 minutes /.9 inverter efficiency/12V = 13 amp hours.

Not a big deal as most people boondocking will have a couple hundred amp hours of battery anyway.

So if you don't want to cart around a generator and wanted to run your microwave for a short period another 40 or so watts of solar would do it. I lug around a genny anyway for reasons explained in my earlier post so I haven't installed an inverter yet. When I do it will be primarily to run my A/C and will for sure require a massive increase in battery capacity.

i agree with you that there are DC solutions for most of the other loads which even if you have an inverter are more efficient.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

Blender Bob View Drop Down

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Joined: 11 Mar 2018
Location: Colorado
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Posts: 48

Posted: 14 Oct 2018 at 8:19pm

Hey offgrid! Thanks replying and for posting the Youtube video regarding pure and modified sine inverters. Very educational and I enjoy the issues it poses. Once again, if I only knew then what I know now. My inverter was cannibalized from another solar project so no $ spent. Good recommendation to avoid modified and buy pure sine inverters.

I do not get the noise/buzz from my HighPoint Microwave EC028KD7 using a modified sine inverter. The video conclusion of 10% to 20% less efficient and performance using a modified sine inverter does not bother my casual use case as things get warm within the time I expect and I’m not toasting my batteries. I suspect FR changes Microwave suppliers from time to time.

I agree, serious microwaving of frozen foods, longer cooking, etc. where microwave time is going more than 10-15 minutes is out of scope and going above 1000w of 110v for any period of time gets into all sorts of issues of larger batteries, cables. Thus, going to genset does make more sense.

Undeterred by failure and costly mistakes, I’m compelled to try things. Thanks again for the discussion.

Bob
2015 Chevy Colorado Z71
2018 178 R-pod Hood River Edition

offgrid

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Joined: 23 Jul 2018
Online Status: Offline
Posts: 5290

Posted: 15 Oct 2018 at 5:33am

Hey Blender Bob,

Glad you're willing to try things, I've found out where they hide the smoke in electrical equipment too many times by now I guess. Please do keep a fire extinguisher handy though when you get compelled to try stuff, I've had to use one more than once over the years. Embarrassed

You have made me curious as to why your microwave runs on a 1200 watt inverter. It's also rated 1500 watts as mine is. Ironically, from looking at that video, I think the answer is that you are using a modified sine wave inverter which the micro doesn't really like and that drops the power requirement down enough to be within range of your inverter. But do keep an eye on the inverter for signs of overheating....

I doubt that the 750 watts you're seeing on the inverter display is accurate though, you'd be seeing really really long warming times. Something more like the 1000 watts shown on the kill-a-watt meter in that video is more likely. It becomes tricky to measure ac power accurately when the voltage and current waveforms have strange (non-sinusoidal) shapes. Do you have a dc current clamp on to measure DC current into the inverter, that's what really counts anyway?

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

GlueGuy

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Joined: 15 May 2017
Location: N. California
Online Status: Offline
Posts: 2627

Posted: 15 Oct 2018 at 9:55am

The watts displayed in a kill-a-watt does not correct for reactive loads. So if the load is highly "capacitive" or "inductive", then that will shift the current and voltage relative to each other. When the sin wave of the current and the sin wave of the voltage are not "in phase", it will give the appearance of a lower wattage.

bp
2017 R-Pod 179 Hood River
2015 Ford F150 SuperCrew 4WD 3.5L Ecoboost

Blender Bob View Drop Down

Groupie

Joined: 11 Mar 2018
Location: Colorado
Online Status: Offline
Posts: 48

Posted: 15 Oct 2018 at 10:45am

I hate when the blue smoke genie gets out! . It's all but impossible to get him back in the box. I do my testing in a barn on a concrete floor with not much around, fire extinguisher near, so safety is always on the mind, especially with voltage. An enjoyable moment for me is when I get a "Gee, that did not fail!" result. Using a microwave is a minor event while camping so my interest this topic is more academic. I would have expected my 1200w inverter to have failed, or batteries to drain faster than they did when I plugged in my HighPoint 1500w microwave. I was thinking I would have to run it on a lower cooking rate, like P7 instead of P10 and wondered where that threshold would be. But it didn't fail. Hmmmm.

I'm not an EE and still Googleing GlueGuys concepts to understand them. I hope to get some college credit at some point. I don't have the tester to measure DC pull off the battery and I see that would be a better test. But, I have calculated the power rate of consumption and the % discharged of the batteries and they are close with some degree of rounding. The microwave works and heats things up so something is happening. Per GlueBuys comments, I believe the answer is beyond by observation. Still observing...

Maybe this discussion warrants a new thread as this thread is about TT tongue...just want to be respectful to the original post.

Bob
2015 Chevy Colorado Z71
2018 178 R-pod Hood River Edition

offgrid

Senior Member

Joined: 23 Jul 2018
Online Status: Offline
Posts: 5290

Posted: 15 Oct 2018 at 11:16am

GlueGuy, I might be wrong but I believe that the kill a watt the guy in the video is using can toggle between va and watts. He replies to a comment below where he says he is measuring watts not va.

When the voltage and current waveforms are out of phase the true power being absorbed my the load is lower that the va. This is not an appearance of lower wattage, power consumed really is lower. Reactive power (VARs) are not true power. so while you are correct that if the voltage and current waveforms are out of phase the true power (watts) reading will be lower than the VA reading, its the watts reading we want. We don't really care about va or reactive power other than it will cause some secondary heating in the inverter and microwave and the conductors between the two. BTW, modern microwaves apparently look pretty much like resistive loads, so should require very litting reactive power.

That being said, we also have the issue here that with a "modified sine wave" inverter we don't have sinusoidal waveforms anyhow. So it depends if your power meter is set up to measure only power in the primary (60Hz) frequency (like the old fashioned rotating disc electric meters are) or measures power flow in the higher harmonics. This is one reason why power companies are installing "smart" meters as fast as they can. With so many loads using switching power supplies nowadays the old disc meters "miss out" on measuring power drawn in the higher harmonics. Lost revenue for them!

I installed a 500kW grid tied PV system on a Whole Food store and couldn't at first figure out where 15% of my expected solar power output went to. Turned out the refrigeration gear in the supermarket was creating tons of higher harmonic noise which the filters in the inverter absorbed trying to clean up the line voltage waveform (PV grid tie inverters must meet ridiculously stringent specs for harmonic noise). I had a GE smart meter on the system which came initially set up to measure true power in all harmonics, so I just reprogrammed it to measure only true power in the primary frequency, problem solved!

Anyhow, all this is why I'm suggesting measuring dc current into the inverter, which is what really matters to us anyway.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

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offgrid Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290	Topic: The tongue of the Rpod Posted: 14 Oct 2018 at 6:09pm
	Its not the size of the inverter that effects the load on the batteries, iIs the size of the load and how long you run it. Energy = power x time. If you're only running the micro a few minutes a day which is pretty typical then its not adding much to your battery requirements. I run mine maybe 6 minutes a day so 1400 watts X 6 minutes /.9 inverter efficiency/12V = 13 amp hours. Not a big deal as most people boondocking will have a couple hundred amp hours of battery anyway. So if you don't want to cart around a generator and wanted to run your microwave for a short period another 40 or so watts of solar would do it. I lug around a genny anyway for reasons explained in my earlier post so I haven't installed an inverter yet. When I do it will be primarily to run my A/C and will for sure require a massive increase in battery capacity. i agree with you that there are DC solutions for most of the other loads which even if you have an inverter are more efficient.
	1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold

Blender Bob Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: 11 Mar 2018 Location: Colorado Online Status: Offline Posts: 48	Posted: 14 Oct 2018 at 8:19pm
	Hey offgrid! Thanks replying and for posting the Youtube video regarding pure and modified sine inverters. Very educational and I enjoy the issues it poses. Once again, if I only knew then what I know now. My inverter was cannibalized from another solar project so no $ spent. Good recommendation to avoid modified and buy pure sine inverters. I do not get the noise/buzz from my HighPoint Microwave EC028KD7 using a modified sine inverter. The video conclusion of 10% to 20% less efficient and performance using a modified sine inverter does not bother my casual use case as things get warm within the time I expect and I’m not toasting my batteries. I suspect FR changes Microwave suppliers from time to time. I agree, serious microwaving of frozen foods, longer cooking, etc. where microwave time is going more than 10-15 minutes is out of scope and going above 1000w of 110v for any period of time gets into all sorts of issues of larger batteries, cables. Thus, going to genset does make more sense. Undeterred by failure and costly mistakes, I’m compelled to try things. Thanks again for the discussion.
	Bob 2015 Chevy Colorado Z71 2018 178 R-pod Hood River Edition

offgrid Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290	Posted: 15 Oct 2018 at 5:33am
	Hey Blender Bob, Glad you're willing to try things, I've found out where they hide the smoke in electrical equipment too many times by now I guess. Please do keep a fire extinguisher handy though when you get compelled to try stuff, I've had to use one more than once over the years. You have made me curious as to why your microwave runs on a 1200 watt inverter. It's also rated 1500 watts as mine is. Ironically, from looking at that video, I think the answer is that you are using a modified sine wave inverter which the micro doesn't really like and that drops the power requirement down enough to be within range of your inverter. But do keep an eye on the inverter for signs of overheating.... I doubt that the 750 watts you're seeing on the inverter display is accurate though, you'd be seeing really really long warming times. Something more like the 1000 watts shown on the kill-a-watt meter in that video is more likely. It becomes tricky to measure ac power accurately when the voltage and current waveforms have strange (non-sinusoidal) shapes. Do you have a dc current clamp on to measure DC current into the inverter, that's what really counts anyway?
	1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold

GlueGuy Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 15 May 2017 Location: N. California Online Status: Offline Posts: 2627	Posted: 15 Oct 2018 at 9:55am
	The watts displayed in a kill-a-watt does not correct for reactive loads. So if the load is highly "capacitive" or "inductive", then that will shift the current and voltage relative to each other. When the sin wave of the current and the sin wave of the voltage are not "in phase", it will give the appearance of a lower wattage.
	bp 2017 R-Pod 179 Hood River 2015 Ford F150 SuperCrew 4WD 3.5L Ecoboost

Blender Bob Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: 11 Mar 2018 Location: Colorado Online Status: Offline Posts: 48	Posted: 15 Oct 2018 at 10:45am
	I hate when the blue smoke genie gets out! . It's all but impossible to get him back in the box. I do my testing in a barn on a concrete floor with not much around, fire extinguisher near, so safety is always on the mind, especially with voltage. An enjoyable moment for me is when I get a "Gee, that did not fail!" result. Using a microwave is a minor event while camping so my interest this topic is more academic. I would have expected my 1200w inverter to have failed, or batteries to drain faster than they did when I plugged in my HighPoint 1500w microwave. I was thinking I would have to run it on a lower cooking rate, like P7 instead of P10 and wondered where that threshold would be. But it didn't fail. Hmmmm. I'm not an EE and still Googleing GlueGuys concepts to understand them. I hope to get some college credit at some point. I don't have the tester to measure DC pull off the battery and I see that would be a better test. But, I have calculated the power rate of consumption and the % discharged of the batteries and they are close with some degree of rounding. The microwave works and heats things up so something is happening. Per GlueBuys comments, I believe the answer is beyond by observation. Still observing... Maybe this discussion warrants a new thread as this thread is about TT tongue...just want to be respectful to the original post.
	Bob 2015 Chevy Colorado Z71 2018 178 R-pod Hood River Edition

offgrid Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290	Posted: 15 Oct 2018 at 11:16am
	GlueGuy, I might be wrong but I believe that the kill a watt the guy in the video is using can toggle between va and watts. He replies to a comment below where he says he is measuring watts not va. When the voltage and current waveforms are out of phase the true power being absorbed my the load is lower that the va. This is not an appearance of lower wattage, power consumed really is lower. Reactive power (VARs) are not true power. so while you are correct that if the voltage and current waveforms are out of phase the true power (watts) reading will be lower than the VA reading, its the watts reading we want. We don't really care about va or reactive power other than it will cause some secondary heating in the inverter and microwave and the conductors between the two. BTW, modern microwaves apparently look pretty much like resistive loads, so should require very litting reactive power. That being said, we also have the issue here that with a "modified sine wave" inverter we don't have sinusoidal waveforms anyhow. So it depends if your power meter is set up to measure only power in the primary (60Hz) frequency (like the old fashioned rotating disc electric meters are) or measures power flow in the higher harmonics. This is one reason why power companies are installing "smart" meters as fast as they can. With so many loads using switching power supplies nowadays the old disc meters "miss out" on measuring power drawn in the higher harmonics. Lost revenue for them! I installed a 500kW grid tied PV system on a Whole Food store and couldn't at first figure out where 15% of my expected solar power output went to. Turned out the refrigeration gear in the supermarket was creating tons of higher harmonic noise which the filters in the inverter absorbed trying to clean up the line voltage waveform (PV grid tie inverters must meet ridiculously stringent specs for harmonic noise). I had a GE smart meter on the system which came initially set up to measure true power in all harmonics, so I just reprogrammed it to measure only true power in the primary frequency, problem solved! Anyhow, all this is why I'm suggesting measuring dc current into the inverter, which is what really matters to us anyway.
	1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold