Running microwave oven with inverter connected to the van battery-with motor running

[hyc]

Hi, All
My 2010 Road Trek 170V, has only one -100 AH (50 in reality) AGM coach battery and 750W inverter. I can only use the microwave oven while on shore power or generator. I am thinking about purchasing a 1500W PSW inverter and connect it to the van's battery (AGM) and only use it to run the microwave oven or a coffee maker (not at the same time) while the motor is running (for maybe few minutes in the morning to get couple cups of hot coffee and hot breakfast when generator or shore power are not available). Microwave oven is 700W with 1000W Max draw. Any thoughts?

[mkguitar]

Originally Posted by hyc

Microwave oven is 700W with 1000W Max draw.

sure this is the draw on the electrical supply?


1000w is 8.333 amps, round up to 9 amps at 120 volts


That same 1000 watts placed on a 12 volt system is 83.33 amps then add some for the inverter


You'd have to set it all up and then use an ammeter on the 12 volt and see what the true draw is on the battery








Mike

[booster]

Originally Posted by hyc

Hi, All
My 2010 Road Trek 170V, has only one -100 AH (50 in reality) AGM coach battery and 750W inverter. I can only use the microwave oven while on shore power or generator. I am thinking about purchasing a 1500W PSW inverter and connect it to the van's battery (AGM) and only use it to run the microwave oven or a coffee maker (not at the same time) while the motor is running (for maybe few minutes in the morning to get couple cups of hot coffee and hot breakfast when generator or shore power are not available). Microwave oven is 700W with 1000W Max draw. Any thoughts?

That is very commonly done, we used to do it on our 07 C190P Roadtrek until we increased battery capacity. You would normally use the coach battery to go with the inverter, as then the inverter cable will also charge the coach battery as it does now without bringing the engine battery into the picture. You also don't want to take a chance on depleting the starting battery. With it on the coach you could then use the inverter on smaller loads on the inverter circuit without the engine running and have the much better PSW inverter power.



The biggest thing you will need to look at is the size of the wiring and the breakers (2) in the cable from the engine to the inverter, assuming you use the existing wiring. You probably have a single #4 cable that is rated at about 80 amps with an 80 amp breaker on each end. If you have the Dometic 700 watt microwave, it will take over 100 amps starting and about 90 amps if at running engine voltage of about 14v. For a short run, you could get by with 4ga as it is heat over time that is the hazard, but to prevent voltage loss you would be better to replace it with a larger cable and breakers.


You have a 100ah battery in the coach, so IMO you should treat it as such as you only have one battery. The 50% use rule they tout as being necessary to prevent battery failure is extremely exaggerated. You don't lose 50% of the life (or more depending on the sales guy's claims) by going down to 20% charge, you actually lose in the 15-20% range. You gain 60% usable capacity, though, so with the low investment of a single battery it is probably well worth the tiny life difference to get the extra power.

[markopolo]

Once the wiring and breakers are sorted out (even temporarily) then you could test it with the Tripp-Lite before buying a new inverter. Those units have an OverPower feature so the 750W unit can supply 1,125 watts.

https://www.tripplite.com/750w-power...tput~RV750ULHW

OverPower™ inverter output supports longer duration overloads to 150% for 1-60 minutes under ideal battery and temperature conditions. (For best results, utilize OverPower usage for as short of a duration as possible, ensure battery bank and cabling is able to provide full nominal DC voltage under load and allow inverter/charger to fully cool before and after OverPower usage.)

Or test the Tripp-Lite running anything that uses 1000 watts.

The 170's only ever had one battery as far as I know so it'll be interesting to find out if RT used 4AWG & 80A breakers like the dual battery capable 190's from around that time period had.

[booster]

Originally Posted by markopolo

Once the wiring and breakers are sorted out (even temporarily) then you could test it with the Tripp-Lite before buying a new inverter. Those units have an OverPower feature so the 750W unit can supply 1,125 watts.

https://www.tripplite.com/750w-power...tput~RV750ULHW

Or test the Tripp-Lite running anything that uses 1000 watts.

The 170's only ever had one battery as far as I know so it'll be interesting to find out if RT used 4AWG & 80A breakers like the dual battery capable 190's from around that time period had.

Good point about the one battery and possible wire size difference. I think they will be the same as the 190s as the 190 used to be offered with one battery stock and the second as an option, but the wiring stayed the same.



If he has the Dometic microwave and the Tripplite MSW inverter it is very unlikely it will run the microwave. The Dometic doesn't seem to like the MSW power and will not even try to start so must be locking out on bad power test. Ours and all I have heard of did similar, as far as I know. Another brand the OP may get by, but would have the reduced microwave output that an MSW inverter gives.

[hyc]

Thank you for the input. Going to do more checking on the existing wire and breaker size. Guess the downside for connecting to the starting battery is having the chance of depleting it and possibly getting stuck with a dead battery. The upside will be not dealing with changing out the existing wiring to the existing inverter and just ran the proper sized wire and breaker from the new PSW inverter to the starter battery and not dealing with the existing Tripp-Lite inverter. If I went with the route of connecting to the starting battery, may be I will get a portable battery jumper/starter as a backup in case I did deplete the starting battery. Also eventually when the coach battery dies, I am thinking replace it with a drop-in LiFePO4 battery.

[booster]

Originally Posted by hyc

Thank you for the input. Going to do more checking on the existing wire and breaker size. Guess the downside for connecting to the starting battery is having the chance of depleting it and possibly getting stuck with a dead battery. The upside will be not dealing with changing out the existing wiring to the existing inverter and just ran the proper sized wire and breaker from the new PSW inverter to the starter battery and not dealing with the existing Tripp-Lite inverter. If I went with the route of connecting to the starting battery, may be I will get a portable battery jumper/starter as a backup in case I did deplete the starting battery. Also eventually when the coach battery dies, I am thinking replace it with a drop-in LiFePO4 battery.

You might find, once you look into the details, that connecting to the starting battery would be just as much work as going to the coach battery. The inverters are not normally considered weather or heat proof do couldn't go under the hood, so would have to run the 12v big wiring to it and find a place for it inside the van. The 110v wiring for the microwave is on the "inverter circuit" which wire directly from the existing inverter in the rear, so you would have to find another way to get the 110v to the microwave, etc. The existing 12v cable to the inverter runs under the van so fairly easy to follow if you can get the van up in the air to get under it safely. If needed it could be replaced with a larger cable or paralleled with another #4 if needed. As mentioned, you may be able to run the micro on the 4 gauge for short runs if the voltage holds up high enough, and with the engine on that is probably what it would do. Then all you would have to would be to go to larger breakers to handle the surge.


The downside of this is that if you increase battery capacity by too much, or charging acceptance of the batteries (too many amps) you might have upsize wiring then.

[jakegw2]

The coffee maker will be the biggest draw - probably 1200W or so, and for a full pot would need this power for up to 15 minutes. Microwave, at a max of 5 minutes and 1000W would be less.

That works out to a peak usage of 300 W/hrs of power (or 0.3KWhrs). Your draw rate will be 1200W / 12v = 100A.

With the van running you can depend on the alternator providing between 40A and 60A of power. For this example, we will use 40A.

That leaves a peak draw of 60A from the battery and 180 W/hr of capacity required (the remaining 40A peak / 120W/hr is provided by the alternator when running).

a single 100A 12V battery will be much less efficient if you draw at a rate of > 5A. A quick check of the chart (https://electronics.stackexchange.co...battery/177036) here tells us we can expect to draw 60A for about 20 minutes before we reach the 12v (which is equal to about 50% state of charge, the lowest we want to go).

60A * 0.3hrs (20min) * 12v= 216 W/hrs available from the battery at this draw level.

Since we needed only 180W/hrs from our calculation above we can see that if you start out with a fully charged battery you can safely run a coffee maker for 15 minutes without damaging your battery as long as your engine is running.

If your battery is not fully charged however it may be a problem. The big variable here is if your alternator produces more that 40A available power (it probably does) and by how much.

A second battery would cut the current draw rate per battery in half, and because lower current draws are much more efficient from lead-acid batteries the available output time would grow from 20min to 60min (or 720 W/Hrs instead of 216 W/Hrs you have now). Getting a second battery would dramatically increase your available power - by over 3x what you have now. You could brew four full pots of coffee in this configuration and open up your own coffee shop in your class B and supply the rest of the campground.

[booster]

Originally Posted by jakegw2

The coffee maker will be the biggest draw - probably 1200W or so, and for a full pot would need this power for up to 15 minutes. Microwave, at a max of 5 minutes and 1000W would be less.

That works out to a peak usage of 300 W/hrs of power (or 0.3KWhrs). Your draw rate will be 1200W / 12v = 100A.

With the van running you can depend on the alternator providing between 40A and 60A of power. For this example, we will use 40A.

That leaves a peak draw of 60A from the battery and 180 W/hr of capacity required (the remaining 40A peak / 120W/hr is provided by the alternator when running).

a single 100A 12V battery will be much less efficient if you draw at a rate of > 5A. A quick check of the chart (https://electronics.stackexchange.co...battery/177036) here tells us we can expect to draw 60A for about 20 minutes before we reach the 12v (which is equal to about 50% state of charge, the lowest we want to go).

60A * 0.3hrs (20min) * 12v= 216 W/hrs available from the battery at this draw level.

Since we needed only 180W/hrs from our calculation above we can see that if you start out with a fully charged battery you can safely run a coffee maker for 15 minutes without damaging your battery as long as your engine is running.

If your battery is not fully charged however it may be a problem. The big variable here is if your alternator produces more that 40A available power (it probably does) and by how much.

A second battery would cut the current draw rate per battery in half, and because lower current draws are much more efficient from lead-acid batteries the available output time would grow from 20min to 60min (or 720 W/Hrs instead of 216 W/Hrs you have now). Getting a second battery would dramatically increase your available power - by over 3x what you have now. You could brew four full pots of coffee in this configuration and open up your own coffee shop in your class B and supply the rest of the campground.

We have found this not to happen this way in our 07 Roadtrek with the various systems we have had in place. Even with the stock 145 amp Chevy alternator it would carry a full 100 amp load for a while before it started to get hot, so no drain on the batteries at all while running the microwave on a 1500 watt Samlex PSW inverter. As long as the alternator and wiring size allow the voltage to the inverter/batteries to hold above 12.7 volts or so, there was never any drain. In a small, one or two, battery system, not using battery for such things is an important item if you want to be off shore power for very long, as you have fairly long recharge times to get past 80% state of charge to replace that use. Preventing the use works much better in the long run.


Personally, if it were my system, I think I would upgrade the alternator if it is small to something in 200+ amp range, add another 4ga cable parallel to the existing one and fuse them at about 140 amps, put bigger cable on the bigger alternator to the separator, add a 1500watt inverter in the rear by the existing charger, add another AGM like the one in the van. We ran almost this exact system for several years and it worked very well for us, although we also had some solar on it. It was only removed when we decided to ditch the generator and also did not want to run the van for anything while offgrid. That change required a lot more work and expense.



A lot of it depends on how the OP is going to use the van and systems, if it is DIY, and how much the budget is.

[mkguitar]

the "larger" the alternator, the more power consumed from the motor which is not going to the wheels


drag cars don;t have 'em


maybe marginal in big picture, but...
energy is never free and we should be as efficient as we can.
I use a percolator on the gas burner for coffee





Mike

[hyc]

Thank You all again for all the good information. Lots to think about. I would love to add a second battery, but for 170, it would be difficult to find space for another battery. I thought of getting an all-in-one portable power station with all the bells and whistles but that got expensive very quickly. One with large enough PWS inverter and lithium battery(lighter weight) can get to $1K very quickly; too rich for "morning conveniences" and thought just getting a decent 1500W PWS inverter (about $300) and some elbow grease will be the most cost-effective way of doing this. I installed a 100W solar with Victron MPPT charge controller a couple of years ago and plan to add another 50W to the system (limited by the roof real estate) this helped a lot on keeping the coach battery charged. Going to do more looking underneath the RT. : )

[booster]

Originally Posted by mkguitar

the "larger" the alternator, the more power consumed from the motor which is not going to the wheels

drag cars don;t have 'em

maybe marginal in big picture, but...
energy is never free and we should be as efficient as we can.
I use a percolator on the gas burner for coffee

Mike

Kind of true, but the actual energy from the engine used by the alternator is directly related to the power being generated. A 100 amp and 250 amp alternator will generally consume about the same power if they are putting out the same amps, as long as they are on the same pulley size so same rotational speed.

[jakegw2]

To be sure. In my van I see the alternator provide around 120A for the first few minutes or so before settling down to around 70A continuous. With these numbers the draw on the battery would be very minimal.

My calculations were based on some very conservative assumptions about the minimum contribution the poster can expect from their alternator.

[markopolo]

Originally Posted by hyc

Thank You all again for all the good information. Lots to think about. I would love to add a second battery, but for 170, it would be difficult to find space for another battery. I thought of getting an all-in-one portable power station with all the bells and whistles but that got expensive very quickly. One with large enough PWS inverter and lithium battery(lighter weight) can get to $1K very quickly; too rich for "morning conveniences" and thought just getting a decent 1500W PWS inverter (about $300) and some elbow grease will be the most cost-effective way of doing this. I installed a 100W solar with Victron MPPT charge controller a couple of years ago and plan to add another 50W to the system (limited by the roof real estate) this helped a lot on keeping the coach battery charged. Going to do more looking underneath the RT. : )

I like the idea of integrating portable LiFePO4 (lithium) power for high current items like a coffee maker or microwave oven. You could also use it in your home during a power outage.

One of my 58Ah packs with a 1500W+ load: https://www.classbforum.com/forums/f23/diy-portable-useful-lifepo4-10057-8.html#post106709

A 50Ah or so portable pack with a 120A or 150A BMS + inverter would easily run your microwave oven if you don't mind discharging at a 2C or so rate.

Keep the portable stuff if you ever sell the RT.

[NAZCamperVan]

HYC, we did a similar computation when adding diy 200w solar panel, battery monitor and new wiring. And decided to omit an inverter altogether. We choose to be non-electric dependent for "morning cooking convenience."

[SteveJ]

Originally Posted by NAZCamperVan

HYC, we did a similar computation when adding diy 200w solar panel, battery monitor and new wiring. And decided to omit an inverter altogether. We choose to be non-electric dependent for "morning cooking convenience."

Non electric for coffee here. We use the pour over system with water heated in a pan on the propane stove.

Other methods using propane incude french press(BTDT, too messy), Aeropress, percolator, and others.

On TDY near Tollgate OR, enjoying a freshly ground pour over cup of coffee on a 52 degree evening.

[rtbill]

An issue with we encountered with running our microwave off an inverter is whether the inverter can ramp up its output quickly enough to satisfy the microwave. If the microwave does not receive adequate voltage and current with a couple of seconds it stops trying to start. I found that switching our absorption fridge to AC would put our inverter in a better state to start the microwave.

A feature of running a microwave off a MSW inverter is that it will not run at full power. Ours runs at about 50% of its output vs being on shore power.

[Rogerp]

We added a 2nd #4 wire from the separator parallel with the existing #4 wire and 80 amp breakers each end. Hooked house pair of 6 volt 220ah batteries to a 1500watt Psw inverter. The inverter has on-counter on/off switch for convenience and only powers the micro oven. We idle the 2000Dodge190P if using the inverter. At idle with mostly charged batteries the voltage is 13.8 and drops to 12.5 for 1/2 a second and settles at +or - 13.6 for the micro run. We only do this for 5 or 10 minutes and no problems in 3 years.