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Old 11-27-2019, 02:46 PM   #1
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Reference for Electrical help near PDX

We had an inverter installed last summer to be fed by our four 6V batteries and our two 120W panels. Its only intended use was to be an infrequent, short run microwave or hair dryer. As such, there was no need to power the interior outlets since we could use the ones on the inverter.
Without providing great detail, suffice to say that the installer informed us that he,'Owes you for an inverter', as he said he 'Blew it up'. We replaced the inverter and now have replaced the batteries (which were +6yrs old, but never discharged below 80%), but 15sec on inverter use throws a low voltage alarm... so we have other problems that need sleuthing.
A Glen Baker in Hood River was recommended. I've spoken to him. But he is unavailable due to a heavy backlog of work.
Since no good deed goes unpunished, my attempt to provide convenience for my wife in our very capable trailer when off grid, has gifted me this vexing set of problems. We need the services of an electrical savant. If you know of one within our reach, we'd appreciate hearing of him/her.
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Old 11-27-2019, 04:13 PM   #2
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Lew Faber is highly recommended. He is located in Hood River 541-490-6357. Not sure if he is still there he works summer there and winter in Florida.



He might be able to guide you. Dave
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Old 11-27-2019, 11:01 PM   #3
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Lew usually leaves in October and returns in late Spring depending on his workload in Naples. The only other shop I would recommend is AM Solar, but their in Springfield, OR (by Eugene). They may be as busy as Glen.
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Old 11-29-2019, 12:06 AM   #4
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I don’t do this professionally, but do live in PDX with a deep understanding of the electrical involved (enough as to never want an inverter). I could possibly do some troubleshooting with a multimeter and inspection, not sure what compensation to expect.

What voltage do you see your batteries at when the issue occurs?
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Old 11-29-2019, 03:12 PM   #5
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That a deeper electrical understanding would lead to a decision not to install an inverter is ominous, to say the least... but I'm intrigued! So...
Fully charged batteries, continuously float charged, then disconnected from charging, show 13.2V and slowly decrease toward 12.8V.
If I then, power the inverter and try to run the microwave, when I get the low voltage alarm (and turn off the inverter), my voltage gauge shows 12.57V. That suggests a huge draw of Amps (somewhere) to me. Again, the batteries are brand new with 440A of capacity. Why that won't run a 1000-1500W appliance with a 2000W inverter escapes my understanding at present. Thanks for the help offered. I'd be happy to bring my problem to Portland and let you look. And, I'd be equally happy to compensate you for unraveling this mystery if you're able to, SilverHouseDreams.
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Old 11-29-2019, 05:06 PM   #6
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You probably need to know the real draw of your microwave (this can be checked with a cheap device like a Kill-a-Watt, but you'd need to get to the microwave's plug which may not be easy depending on the installation.)

You should measure voltage at the batteries and/or the input terminals of the inverter when you're testing this. Too-small wiring between the batteries and the inverter could do this, as could a poor connection on that route.

The 12.57v you're seeing right after you run the test is not necessarily indicative... it'll probably come up quite a bit in 5-10 minutes of "rest" after that big fast draw-down. You're probably pulling 100A or so at 12v while the microwave is running, after all.
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Old 11-29-2019, 08:00 PM   #7
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Sounds like you are not getting full power from the batteries easy things to look for.

1. The inverter needs to be as close to the batteries as possible.
2. Correct wire size depends on distance from batteries 4ft 4 gauge, 10ft 2 gauge.
3. Inverter + and - connections across "all" 4 batteries.
4. All connections must be clean and very tight.
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Old 11-29-2019, 11:14 PM   #8
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Thanks, Garry. You've hit on a couple of avenues I need to pursue;
" 3. Inverter + and - connections across "all" 4 batteries. "
" 2. Correct wire size depends on distance from batteries 4ft 4 gauge
My batteries are pretty close, but cables may be 5-8'. Will need to mic the diameter if there are no gauge markings.

DKB - our microwave has an output lot of 1000W, so it shouldn't be drawing even 9A. Our voltage drawdown suggests (like Garry says) that not all four batteries are contributing their amps.

BUT... frying the first inverter leaves me with an uneasy feeling about how localized our problem may or may not be.

Thanks to all for the headwork.
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Old 11-29-2019, 11:31 PM   #9
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Read that whole label. Remember that nothing is 100% efficient... 1000w is the rated output of microwave energy, the label says its energy consumption is 13A at 120v, which with a 100% efficient inverter would require 130A at 12v. Your batteries are starting at a bit more than 12v, but your inverter is just a bit more than 90% efficient if it's a good one. TANSTAAFL.
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Old 11-30-2019, 12:59 AM   #10
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It sounds to me like you had the same problem I had on my last trailer, wires too small from the batteries to the inverter and between the batteries. The voltage drop can be surprising when you are drawing close to 150 amps. When I rewired my current AS I ran 02 wire (not 2 ga) everywhere between the batteries and to the inverter but would have gone to 04 if I had a long run.

It may seem excessive but it solved my problem.

You could test that theory by removing the inverter and temporarily connecting it with a short heavy wire (2 ga or bigger) directly to the four batteries. Then plug in a hair drier and see if it gives you a low voltage alarm.

With four 6v batteries you must have two pairs of series connected batteries so there are quite a few short wires connecting them. Those losses could add up if they are undersized or not making perfect contact.
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Old 11-30-2019, 03:05 PM   #11
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Good additional info and points to consider... thanks! While wire sizing has been adequate for the 10yrs of off grid camping we've done since I upgraded our electrical supply/storage, it was all 12V DC use. The inclusion of an inverter allowed me to assume that it would be compatible with my existing arrangement. My (also assumed) protection, was having a pro do the inverter installation. The unhappy result is reminding me to get my head further into the problem. The easiest and first action will be upsizing cables (which I believe I can do simply, by doubling each existing member if all posts allow space to secure them). A subsequent test would then offer a before/after comparison. More to do as we begin to navigate the holiday season . Will report as we proceed.
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Old 11-30-2019, 11:15 PM   #12
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Originally Posted by nwclassic
The easiest and first action will be upsizing cables (which I believe I can do simply, by doubling each existing member if all posts allow space to secure them). A subsequent test would then offer a before/after comparison. More to do as we begin to navigate the holiday season . Will report as we proceed.

Doubling is not recommended, unless you somehow fuse them independently. Otherwise if you are under the full load that is OK with 2 leads, but one fails...then you are doubling the load on the remainder, which could fail less gracefully.

As for not wanting an inverter, I don’t have the luxury of a massive battery bank in my 22FB...nor the wall of solar to recover one. Inverters are not very efficient, they really make boondocking a challenge if you can’t find paths to exist on 12VDC and propane. I have yet to find anything I need 120VAC for that I can’t survive without, or do natively at 12V. So many applications are just converting 120VAC back to DC anyway, those efficiency curves don’t matter when you are on utility power...but become painful on battery banks.
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Old 12-01-2019, 12:50 AM   #13
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Originally Posted by nwclassic View Post
Good additional info and points to consider... thanks! While wire sizing has been adequate for the 10yrs of off grid camping we've done since I upgraded our electrical supply/storage, it was all 12V DC use. The inclusion of an inverter allowed me to assume that it would be compatible with my existing arrangement. My (also assumed) protection, was having a pro do the inverter installation. The unhappy result is reminding me to get my head further into the problem. The easiest and first action will be upsizing cables (which I believe I can do simply, by doubling each existing member if all posts allow space to secure them). A subsequent test would then offer a before/after comparison. More to do as we begin to navigate the holiday season . Will report as we proceed.
Depending on what wire size is there doubling it may or may not be enough. I suggest as a target you are looking for the same resistance per meter as 02 gage wire. This chart will tell you what you’d need to add to get there.

The 150 amp draw from an inverter is a completely different kettle of fish from what Airstream had in mind for a 12v only setup. If you’re currently using the original 4ga-6ga wires to drive the inverter then that’s definitely the problem.

My take on inverters is that I wouldn’t go without one. I used the Victron Multiplus 3000 to electrify all the outlets in the trailer off battery. We use hair driers, induction cooktops, microwaves, TV, just like home. I needed to use Lithum batteries for space reasons, though.
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Old 12-11-2019, 11:34 AM   #14
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Originally Posted by nwclassic View Post
We had an inverter installed last summer to be fed by our four 6V batteries and our two 120W panels. Its only intended use was to be an infrequent, short run microwave or hair dryer. As such, there was no need to power the interior outlets since we could use the ones on the inverter.
Without providing great detail, suffice to say that the installer informed us that he,'Owes you for an inverter', as he said he 'Blew it up'. We replaced the inverter and now have replaced the batteries (which were +6yrs old, but never discharged below 80%), but 15sec on inverter use throws a low voltage alarm... so we have other problems that need sleuthing.
A Glen Baker in Hood River was recommended. I've spoken to him. But he is unavailable due to a heavy backlog of work.
Since no good deed goes unpunished, my attempt to provide convenience for my wife in our very capable trailer when off grid, has gifted me this vexing set of problems. We need the services of an electrical savant. If you know of one within our reach, we'd appreciate hearing of him/her.
Give AM Solar, Springfield, OR a call. They do excellent work and sell first class components.
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Old 12-11-2019, 12:02 PM   #15
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4 batteries should cope with short bursts of a microwave.

Can you check if there is a selectable setting on the inverter for Low Voltage Cutout and Low Voltage Alarm

Both should be set at around 11 volts or even lower, certainly not 12.4v you are talking about
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Old 12-11-2019, 01:07 PM   #16
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4 batteries should cope with short bursts of a microwave.

Can you check if there is a selectable setting on the inverter for Low Voltage Cutout and Low Voltage Alarm

Both should be set at around 11 volts or even lower, certainly not 12.4v you are talking about
Good suggestions. It was what I was going to ask.

I have two dual 6v batteries (Trojan T-105) wired into an older Xantrex 1000 watt inverter. The run from the batteries to the inverter is about 6' using 2 gauge solid wire. I run a small Mr Coffee pot off of the inverter and have never had any low voltage issues. I think it's rated at 600 watts and I don't recall the amps. I have never tried running the microwave off of the inverter, mainly because I think the inverter isn't rated for it. I muddled my way through the install myself after extensive reading of the Xantrex manual as well as online research.
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Old 12-11-2019, 01:47 PM   #17
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All great replies from others. As just another possible piece of your puzzle, I've run large 1200 & 2000+ watt inverters since the early 1980's when Heart Interface was a popular brand (now Xantrex). I've run all kinds of brands since, even replacing all the MOSFET's in one just to "tune it up" and a few JFET's in another, and both modified and pure sine-wave models on many different size microwaves. The other commenters covered most of the common issues - especially the wire sizing - although those voltages you listed remind me of a few I've seen when the batteries are recharged with a single stage charger before 4 stage higher voltage chargers became common place - but I would assume your solar panels have a staged charger already, so probably not the same cause in this case.


But the symptoms you described remind me of something that I didn't notice mentioned in any of the other comments, and it's real common, because even many RV manufacturers still wire battery banks without considering balance. When I first put a 2000 watt inverter in our Airstream motorhome, I installed larger wires to the inverter to match the expected load, but it would only run the microwave for a few minutes before kicking out due to low voltage. The battery voltage would then bounce back up above 12 volts in short order, but still the same effect when tried again. Previously, the factory inverter was only a small 130 watt unit powering a TV and never exhibited that problem because it never drew such a huge amount of amps like the larger one did.


What I figured out was that the factory simply hooked both cables up to the first battery and then paralleled the second battery with short cables - making the inverter pull most of the load off the first battery and leaving the second battery to "refill" the first one as best it could, which is why the voltage "recovered" after a few moments. When I installed the larger cables for the inverter, I simply hooked the cables to the same terminals. The answer was simple - hook one cable to the first battery (example: the + terminal) and hook the other cable (example: the - terminal) to the second battery and then use the remaining short cables to complete the parallel coupling. Even though my battery bank is admittedly undersized, that simple change allowed me to run the microwave around 15 minutes with no other changes because it was now drawing power from both batteries instead of only one at a time.


There are diagrams on the web of common battery hookups, especially 2, 4, & 6 battery type banks - search on "battery balanced hookups". I've worked on many units over the years, especially motorhomes, where they were wired unbalanced right from the factory - but nobody noticed the difference until something that draws huge loads like a large inverter was added.


Good luck and I hope that helps in some way!
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Old 12-11-2019, 05:14 PM   #18
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Thanks to all for very useful and insightful info. My current (excuse the pun) plan is to replace all cables with 2/0. It will take some doing, as I have cable runs from the battery compartments to a box between the forward couch and front wall, then to our three stage charger. The inverter is mounted in the couch drawer, which yields the shortest possible cable lengths. There'll be some refitting of the battery box to maintain the venting path through the other battery compartments.
There is every possibility that my bank is not balanced for supplying all amps to the inverter. I'll pay close attention to where those two cables go (from the inverter). If all else fails, I'll give AM Solar a call. With a holidays looming, it may be awhile before I can post a 'Here's what happened' update... but I will. Best to all. Much appreciated.
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