Ram Promaster Forum banner

1 - 20 of 81 Posts

·
Registered
2014-159 HR in CT
Joined
·
3,661 Posts
Discussion Starter #1
OK, here's the scenario:

-6 month old 100AH AGM battery fully charged, voltage reading about 12.6
-700W Microwave (uses about 1000W)
-HF 1500W (3000 surge) inverter connected with 2 feet of #6AWG (doesn't get warm at all)
-1 cup of water in mug
-No solar, just a 150A isolator that charges battery whenever I drive - works great for TV and most loads....

I turn on the microwave... it sound different than on household AC, kind buzzy
Voltage meter drops to about 11.8 volts.
About 3 minutes in, inverter drops out
Water hot but not quite boiling yet....

Your thoughts are welcome! I'd like to be able to do a 5-10 microwave cooking thing occasionally....

I'm wondering if I ran the van and let the battery isolater link the batteries, would that do any harm to the van electrical? I have the stock alternator, not the HD one. I tried it but I have a 25A fuse going to the isolater. It popped. I know, I need a bigger fuse and will try that, but....

I was hoping to not have to start the van to use the microwave. Insights are requested, please :D

Ed
 

·
Registered
Joined
·
167 Posts

·
Registered
Joined
·
625 Posts
I'd wager there's a few things going on here...

- That 700W microwave probably does use 1000W, or maybe closer to 11-1200W. I've read of some 700W micros tripping a 1000W inverter. You have a 1500W inverter, not a problem there, but just to note the actual power draw.

- Harbor Freight inverter? Its probably a modified sine wave, not a pure sine wave. Many electronics will do OK on a modified sine output, but microwaves prefer a pure sine. They will be noisier and take longer on modified sine wave.

- Its only 2' of #6 wire, but I would say that is undersized for a 1500W inverter. Looking at the wiring specs for a Magnum 1500W it specs a #2 wire for a short length, for a 5% voltage drop. The specs for my Magnum 1000W specs a #1 /0 wire to handle the maximum possible draw at low voltage. Even though its not feeling warm, your #6 is likely undersized, leading to voltage drops, which is never good.

- The DC current draw for a 1000W output is large. When a lead-acid battery has a large current draw, it drops voltage, and capacity as well. (advantage: lithium) Your 100AH battery is probably not large enough to run the 1000W output needed for the microwave. Upgrading to a 200AH battery would help.

A few of those combined leads to a low voltage at the inverter, after a bit of use the voltage drops further, reaching its low-voltage cut-out.


As for running the van to do this, you're right, it would likely need a MUCH larger fuse, which may not be good idea.


In sequence I would look at


1: updating to larger cabling for the inverter, at least #2 , if not #1 /0
2: upgrading to a 200AH battery
3: changing to a pure sine wave inverter
 

·
Super Moderator
Joined
·
10,544 Posts
I have pretty much the same micro setup (700 watts) only I have 2 - 100AH AGM's and a cheap 2k inverter from HF. It works fine. Sometimes I do turn the engine on to give it an extra boost, (like early in the AM when the batteries are at their lowest after running the fridge all night and before the sun comes up) but I never have a problem during the day or at suppertime.

I think you need a second battery.
 

·
Registered
Joined
·
654 Posts
Question: Would an induction range top have the same current drain (and corresponding voltage reduction?)?
It seems so, but that it may be more efficient than a microwave?
 

·
Registered
2014-159 HR in CT
Joined
·
3,661 Posts
Discussion Starter #6
Question: Would an induction range top have the same current drain (and corresponding voltage reduction?)?
It seems so, but that it may be more efficient than a microwave?
According to Nuwave, (http://www.nuwavepic.com/faq.asp question #12 ) 600 actual Watts gets you up to 270 degrees. That would be less than a microwave, if true.

I'm going to do more research on that!

Ed
 

·
Registered
2014-159 HR in CT
Joined
·
3,661 Posts
Discussion Starter #7
I have pretty much the same micro setup (700 watts) only I have 2 - 100AH AGM's and a cheap 2k inverter from HF. It works fine. Sometimes I do turn the engine on to give it an extra boost, (like early in the AM when the batteries are at their lowest after running the fridge all night and before the sun comes up) but I never have a problem during the day or at suppertime.

I think you need a second battery.
KOV,

How big is the fuse from your van battery thru isolater to aux battery(s)? stock or upgraded alternator?

Did you ever notice what the voltage is while microwaving?

I remembered that someone had a similar setup, but couldn't remember it was you.

Thanks,

Ed
 

·
Registered
Joined
·
17 Posts
I second the second battery and upgrade the wire size as well. Then try it and see if you can get away with the modified sinewave inverter..if not, spend some money on a new inverter...sorry....Jim Lofgren
 

·
Super Moderator
Joined
·
10,544 Posts
KOV,

How big is the fuse from your van battery thru isolater to aux battery(s)? stock or upgraded alternator?

Did you ever notice what the voltage is while microwaving?

I remembered that someone had a similar setup, but couldn't remember it was you.

Thanks,

Ed
I'd have to look but I think its 150 A or maybe even 175A. Stock alternator. The voltage varies while microwaving but it usually is about 12.4 - 12.6. Never had a problem with it working and I only start the engine up as a precaution in the AM (I very rarely use it in the AM).
 

·
Registered
Joined
·
428 Posts
I have a similar setup except that my battery is size 8D about 230 amp hours. My inverter is pure sine wave from Xantrex. Inverter is only 1000 watts but capable of much more for a very few minutes. It indicates that battery current is about 120 amps; that is, the 700 watt microwave is using 1000 watts or more. If I run the microwave for more than 3 minutes I let the battery rest and inverter cool down for a couple of minutes before continuing. I have an 80 amp fuse from the engine battery to the combining relay. I never run the engine with the microwave or my 750 watt hot water heater as I think it might blow the fuse as I assume that all the current would come from the alternator as it would see well below 12 volts. You need both a bigger battery and a pure sine wave inverter.
 

·
Super Moderator
Joined
·
10,544 Posts
I'd try another battery first. As I said before I have a cheap Harbor Freight 2k inverter and it has never let me down.
 

·
Registered
Joined
·
654 Posts
Somewhat OT, but Webasto has a diesel cooktop, but it takes 15 minutes to boil 1 liter of water. It has 1.8kw of heat input. That sounds like a long time to boil water.
 

·
Registered
Joined
·
49 Posts
My 100ah battery runs a welder on a 4000 watt pure sine inverter with a 12kw surge. I would lean toward battery cable size rather than battery.
 

·
Premium Member
2014, 138WB, High Roof, Gas, SW MT
Joined
·
2,086 Posts
OK, here's the scenario:

-6 month old 100AH AGM battery fully charged, voltage reading about 12.6
-700W Microwave (uses about 1000W)
-HF 1500W (3000 surge) inverter connected with 2 feet of [URL=http://www.promasterforum.com/forum/usertag.php?do=list&action=hash&hash=6]#6 AWG[/URL] (doesn't get warm at all)
-1 cup of water in mug
-No solar, just a 150A isolator that charges battery whenever I drive - works great for TV and most loads....

I turn on the microwave... it sound different than on household AC, kind buzzy
Voltage meter drops to about 11.8 volts.
About 3 minutes in, inverter drops out
Water hot but not quite boiling yet....

Your thoughts are welcome! I'd like to be able to do a 5-10 microwave cooking thing occasionally....

I'm wondering if I ran the van and let the battery isolater link the batteries, would that do any harm to the van electrical? I have the stock alternator, not the HD one. I tried it but I have a 25A fuse going to the isolater. It popped. I know, I need a bigger fuse and will try that, but....

I was hoping to not have to start the van to use the microwave. Insights are requested, please :D

Ed
Hi,
On the #6 wire.
If the input to the microwave is 1000 watts, and the inverter is 90
% efficient, then the current from battery to inverter is about (1000/0.9)watts / 12volts = 93 amps.

This voltage drop table: http://www.solarseller.com/dc_wire_loss_chart___.htm
says that a #6 wire can be up to 2.9 ft long for 2% voltage drop at 100 amps current flow. 2% voltage drop is only 0.2 volts, so while it seems like something heavier than #6 would be a good idea, its probably not the basic cause of the problem.

I agree with the others that you probably need more battery.

Gary
 

·
Registered
Joined
·
167 Posts
OK, I do run #6 gauges wires too:D
but I do run it in parrallllleL:eek:
So, my total summary of a cable 6 / 3 = 2gauges.
It was much cheaper to by jump-cabels #6 gauges cut it and run 3 connected in PARALEL :D
 

·
Registered
2014-159 HR in CT
Joined
·
3,661 Posts
Discussion Starter #16 (Edited)
Lots of good info and experiences here. Thanks!

A few thoughts...

autogateman,

The math doesn't work. To get 4000 watts from a 12V battery (with no wire losses), you need a 333Amp battery. I'm guessing that the welder you use pulls less than 1000 watts, and that's why it works. I've looked at uNik's posts and he uses 3 batteries to weld.

KOV, Gary,

It appears that a second battery is in my future! What I don't understand is how KOV's battery stays at 12.x volts when mine drops into the 11v range almost immediately. I think we have the same microwave, based on the description (HD, 700W Magic Chef). At a 5 amp discharge rate, my battery pretty much offers about 24 hours of use, which confirms 100Ah rating.

KOV, where's you get that battery? Brand, model number? Do you run the microwave at full power or lower power for a longer time?

My thinking is to beef up the connection between the van battery, isolater, and house battery. On my Battery Doctor Wizard, there is a button that puts the van and house batteries in parallel. Seems to me that would be the same as a second house battery. I'm going to try an 80A fuse from van battery to isolater and see what happens with the "parallel button" on.

I'm hoping the van+house batteries will work for occasional use. Not sure if running the van is a good idea because it's hard to determine how much of the alternator's amps are available to contribute to the required 80+ amps. Don't want to create any alternator circuitry repair issues! OTOH, it might make it all work, and I have no problem running the van to use the microwave.

Thanks guys,
Ed
 

·
Registered
Joined
·
49 Posts
Lots of good info and experiences here. Thanks!

A few thoughts...

autogateman,

The math doesn't work. To get 4000 watts from a 12V battery (with no wire losses), you need a 333Amp battery. I'm guessing that the welder you use pulls less than 1000 watts, and that's why it works. I've looked at uNik's posts and he uses 3 batteries to weld.

KOV, Gary,


Thanks guys,
Ed

The short term amperage capacity of the battery is much higher than 100amps. My welding machine draws 20 amps AC at full current. That's almost 3000 watts.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
314 Posts
I bought an inverter type microwave for my build, they are lighter and the power level is adjustable rather than the typical microwave which cycles on and off at full power. Amazon around $100.
 

·
Super Moderator
Joined
·
10,544 Posts
Lots of good info and experiences here. Thanks!

A few thoughts...

autogateman,

The math doesn't work. To get 4000 watts from a 12V battery (with no wire losses), you need a 333Amp battery. I'm guessing that the welder you use pulls less than 1000 watts, and that's why it works. I've looked at uNik's posts and he uses 3 batteries to weld.

KOV, Gary,

It appears that a second battery is in my future! What I don't understand is how KOV's battery stays at 12.x volts when mine drops into the 11v range almost immediately. I think we have the same microwave, based on the description (HD, 700W Magic Chef). At a 5 amp discharge rate, my battery pretty much offers about 24 hours of use, which confirms 100Ah rating.

KOV, where's you get that battery? Brand, model number? Do you run the microwave at full power or lower power for a longer time?

My thinking is to beef up the connection between the van battery, isolater, and house battery. On my Battery Doctor Wizard, there is a button that puts the van and house batteries in parallel. Seems to me that would be the same as a second house battery. I'm going to try an 80A fuse from van battery to isolater and see what happens with the "parallel button" on.

I'm hoping the van+house batteries will work for occasional use. Not sure if running the van is a good idea because it's hard to determine how much of the alternator's amps are available to contribute to the required 80+ amps. Don't want to create any alternator circuitry repair issues! OTOH, it might make it all work, and I have no problem running the van to use the microwave.

Thanks guys,
Ed
Ed, I also have #6 cable from the batteries to the inverter. The batteries are from Sam's, 2/12v AGMS ($180 each as I recall). If I use the micro it's only for 2-4 mins usually on high power. If I remember I'll do a voltage check for you with it running on just the house batteries and then combined with the alternator. Memories aren't always what the used to be:laugh:
 

·
Registered
Joined
·
2,098 Posts
Ed, I also have #6 cable from the batteries to the inverter. The batteries are from Sam's, 2/12v AGMS ($180 each as I recall). If I use the micro it's only for 2-4 mins usually on high power. If I remember I'll do a voltage check for you with it running on just the house batteries and then combined with the alternator. Memories aren't always what the used to be:laugh:
That data would be great to know. I'm considering a similar upgrade and would also benefit from knowing what actually happens with batteries when running a small microwave (or coffee maker) for a few minutes.

By the way, can you report on your batteries brand and size. Knowing Amp-hours would help replicate results.
 
1 - 20 of 81 Posts
Top