Input requested on electrical issues

[nyyankees588]

[font=Tahoma, sans-serif]Hi there - I have now been living full-time out of my van for the past month. When I installed my electrical system, all appeared to be well and good, however a few significant issues have appeared over the past couple of weeks that I am trying to diagnose. My guess is that they are all related, but the possible problems are many and my electrical knowledge is relatively limited. Any input would be greatly appreciated - I've provided as much detail as possible below and will provide additional info that may be needed.[/font]
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[font=Tahoma, sans-serif]Problems[/font][font=Tahoma, sans-serif] (specs of components are all listed in section below):[/font]
[font=Tahoma, sans-serif]- Fridge triggers inverter fault: I made a DIY residential freezer to fridge conversion and unless the batteries are at full charge and either currently receiving current from the solar panel or van (via an isolator), the fridge triggers the inverter to fault when it turns on. The fault error code is for under voltage from the batteries OR poor battery condition. I fridge pulls 135 watts when it first turns on and a steady 60 watts once it is on and the compressor is running. When I originally got the fridge and tested it plugged in to a house, the overall energy usage was very small – between 20-30 amp/hours per day. My best guess is that despite this low overall usage, it pulls too much power for my battery system to handle for the very brief amount of time that it is turned on. [/font]
[font=Tahoma, sans-serif]- Batteries hold charge erratically: At this point I keep the fridge turned off and only turn it on to cool when the van is on (so that the batteries are receiving full power from via the isolator and can handle the fridge). When I originally had the fridge hooked into the system, the batteries would experience wild swings in charge level when the fridge turned on/off (I monitored the % and voltage via my charge controller). With the fridge turned off however, I have noticed that the batteries continue to experience wild swings in charge. For example, last night they went from 100% charge to 5% charge (according to my charge controller) after having my interior lights on for ~1hr (they draw very minimal energy). When charging 2 laptops through the inverter (drawing 60 watts total), the batteries have also dropped charge almost immediately (when I unhook the laptops they shoot back up to ~80% charge).I have owned the batteries for under 2 months, but I am wondering if they are shot (possibly as a result of being used with the fridge that overdrew them?).[/font]
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[font=Tahoma, sans-serif]Electrical setup/components:[/font]
Solar: 275 Watt Residential Panel
Batteries: 2x 6v Trojan T-105 (setup in 12v system, 225amp/hr total power capacity)
Isolator: Keyline 140amp Smart Isolator
Inverter: Xantrex ProWatt 1000W Pure Sinewave
Charge Controller: Renogy 20amp Rover
Fridge: 2.1 cu ft chest freezer converted to chest fridge via STC-1000 temperature controller (when fridge hits set temperature, controller triggers fridge to turn on until it reaches set temp, at which point it cuts power to fridge).
Lights: Acegood RV/Boat recessed lights x8

 

[frater secessus]

(wild speculation follows)

If the bank is chassis grounded I I suspect a bad ground.  

If the ground is good then the possibly batteries, but flooded batts really are resilient. Have you checked water levels lately?  {Edited to add:  if it is the batteries, remember that murdering a battery bank is something of a rite of passage.}

If the inverter is wired to a bus bar or other distribution point I suspect wiring between the bank and bus, and/or between the ground and the bus..

Keep us posted on what you try and what the results ae.  I'd really like to know what it is.

{also edited to ask:  Do non-inverter loads cause the same behavior?}

 

[tx2sturgis]

Recently a friend had problems somewhat similar to this.

Everything worked fine at first, then a few weird things began happening.

It turned out to be two loose connections at the controller and one loose battery connection. Sometimes things worked, sometimes they didn't.

Batteries move around, connections can oxidize, sometimes wires and cables get jostled a bit during travel, and sometimes the screws, bolts or clamps just weren't tightened enough, or lock washers weren't used, or the copper or lead terminals 'mash' a bit...stuff happens.

Go to the trouble to physically make sure that EVERY connection is secure, even if you have to dig in deep to get to them.

 

[John61CT]

Just checking, 60W consumption while cycling is ~5A @12V, not that much greater than DC compressor models, depending on temperatures.

When you tested at home, were you measuring DC12V amps consumption, or just AC without the inverter?

If the former, was the same battery bank in use then?

 

[Weight]

1000W is borderline or a bit small for a household appliance. 225 amp hour battery is a bit small. What awg and length are your cables from the battery to inverter? How many times have your batteries been discharged to a point of not working?

 

[John61CT]

That size bank in itself is not a problem, as long as in good health and properly cared for.

If so, you're right voltage drop over wiring is likely, inverter should be close to the bank with thick enough gauge cable.

Measure tge DC voltage at the inverter, before turning the fridge on, then during the cycling.

 

[nyyankees588]

Thanks everybody for the input... did a bit more trouble shooting today and will see how things go over the next 24hrs. Additional info below and responses to everbody.
Additional thoughts:
Both the charge controller and inverter have built in fault mechanisms that cut power if the detected battery voltage drops below a certain amount (10.5V for the inverter, I don't remember the default setting for the controller). Part of the issue is that when the fridge compressor kicks on, the battery voltage detected by the inverter & controller drops drastically and can force either/both to cut power momentarily. When this happens, the voltage detected by both jumps back up to the normal level. I don't quite understand that translation between the battery voltage, amperage and charge percentage. Would this suggest that the fridge pulls too much power when it's on (even though, averaged out over the time that it's on/off, that total power pull is small?

Responses:
Frater: Both the inverter and batteries are grounded to the chassis. I checked the ground today and it seemed solid, I did re-tighten it to be certain. They are grounded via the same chassis connection due to be located next to each other. From my understanding, this shouldn't be a problem. The battery water levels are good to go and I checked ALL the connections today to be sure that they were tight. My batteries are wired in a series and the inverter isn't connected to any bus bars (it has two regular AC plugs coming out of it that power strips are plugged in to).

Stugis: thanks for that - I did check/tighten all of my connections today. The only ones that seemed to be slightly loose were a few of the nuts connecting things to the battery terminals. What's the best way to keep these from wiggling lose? Right now they're just tightened via a straight nut without any lock washers, etc. Would a lock washer be appropriate item to add between the nut and the wires that connect to the batteries?

John: When I tested the fridge at home it was hooked up to AC power without the inverter (I didn't have a way to charge the batteries to test it with 12v power). The inverter has a built-in voltage meter and it and my charge controller seem to give the same voltage readings, so my assumption is that the inverter is receiving the full power from the batteries. Would swapping out the 4 gauge wires for 2 gauge or larger wires between the inverter/batteries be worth it?

Weight: The small size of the inverter/battery bank was my fear also, but there are many examples of people doing similar residential freezer-to-fridge conversions and using even smaller setups (600W inverter, smaller batteries). My thought is that the freezer is started with is bigger than what most people use (2.1 cu ft vs. typical 1.6 cu ft dorm freezer) and therefore the compressor may draw more power than what other people use. The inverter to battery cables are 4 gauge (ground is 2 gauge). The positive wire runs through a 100amp in-line fuse to the battery. The distance between the batteries and inverter is <12 inches, so they're super close.

 

[John61CT]

When I tested the fridge at home it was hooked up to AC power without the inverter (I didn't have a way to charge the batteries to test it with 12v power). The inverter has a built-in voltage meter and it and my charge controller seem to give the same voltage readings, so my assumption is that the inverter is receiving the full power from the batteries. Would swapping out the 4 gauge wires for 2 gauge or larger wires between the inverter/batteries be worth it?

Assume nothing. Put a DMM on the inverter terminals first as I wrote. If your voltage isn't dropping due to wiring, changing that does nothing.

Try the same when the batts are known 100% Full, plus while a high-amp charge source is running at the same time.

 

[tx2sturgis]

The only ones that seemed to be slightly loose were a few of the nuts connecting things to the battery terminals. What's the best way to keep these from wiggling lose? Right now they're just tightened via a straight nut without any lock washers, etc. Would a lock washer be appropriate item to add between the nut and the wires that connect to the batteries?

Slightly loose is not good...this can sure cause some problems...amps going in to the battery and amps coming out of the battery don't like 'loose' connections and can misbehave!

You can add a stainless lockwasher and stainless flat washer, on each battery terminal, between the ring terminal and the nut, bolt, or wingnut, whatever you have. 

A light coating of your choice of protective dielectric grease or anti-ox will help preserve the connection.

 

[tripper]

I believe you can add a hard start capacitor to the refrigerator compressor and that should significantly lower the initial voltage draw on your inverter. I do believe your problem is a bad ground/bad connector/bad wiring issue.

 

[Weight]

Your 4awg is ok for 1 foot and 150 amps. I use larger fuse sizes to reduce voltage drop. Fuses protect the wire, not the device. If you have positive feed and negative return from the inverter. Two cables. The case ground can go to the chassis if the battery negative also connects to chassis. Loose connections cause voltage drop. Connection at the battery; battery stud/cable lug/flat-washer/lock-washer/nut. Everything shinny metal. Not a wing nut. Use a hex nut. Torque to 110 inch pounds. Some use a nylon insert type lock-nut. I recommend stainless nut and lock-washer. Are you sure your batteries are fully charged?

 

[Trebor English]

Part of the issue is that when the fridge compressor kicks on, the battery voltage detected by the inverter & controller drops drastically and can force either/both to cut power momentarily. When this happens, the voltage detected by both jumps back up to the normal level. I don't quite understand that translation between the battery voltage, amperage and charge percentage. Would this suggest that the fridge pulls too much power when it's on (even though, averaged out over the time that it's on/off, that total power pull is small?

  
The charge controller indication of state of charge percentage is bogus.  Get a hydrometer and measure the acid in the battery to actually find out whether your batteries are charged or not.  The charge controller percent full is based on battery voltage.  That's why it can change quickly.  The actual state of charge changes slowly.  

When the fridge compressor starting surge load pulls the battery down that is consistent with a bad wire or an undercharged or sulfated battery.  Those conditions can be diagnosed with a hydrometer.  Get one, they are cheap.  

Charge your battery.  If you stop all loads except some small minimal led lights and one phone and verify that your battery is getting charged you can get the battery charged.  It might take several hours to get to 14.8 volts.  If that happens quickly you either have a fully charged battery or a sulfated battery.  Look for 14.8 volts at the battery for several hours.  Look (through safety glasses or plastic wrap) for bubbling of the electrolyte.  Since you don't have an amp meter you can't verify that the charge current is reducing to less than two amps with 14.8 volts applied.  That would mean full if the hydrometer agrees.  If that sort of charging doesn't get the specific gravity back up then sulfation is the problem.  

You may have a bad wire or bad connection.  While current is flowing measure voltages.  For example, there is a cable connecting the two batteries in series.  Measure the voltage between the two batteries.  Where the grey lead metal comes through the maroon plastic case on one battery to the other battery lead will show any bad connection.  There are several components.  There's battery, terminal, wire, other terminal, other battery.  Use the lowest voltage scale on your meter.  Check all the connections with a substantial current.  I use an old headlight bulb to create a 5 amp current.  Make a list of voltage drops and look for something inconsistent.  Battery minus to chassis, battery to battery, battery plus to inverter, battery plus to charge controller, battery minus to inverter minus, etc.  

Your system should be possible.  I have a 1.7 cubic foot Haier fridge, a 400 watt $25 Harbor Freight inverter, a 75 amp hour battery, one 100 watt solar panel an a cheap PWM solar charge controller.  Due to the small battery I only run the compressor when it is sunny.  The biggest wire I have is AWG # 6.  I have and use a hydrometer.  

Advance auto parts web page has battery hydrometers of the style I don't like for $10 to $12.  The O'Reilly web page has the glass tube with float style I like for $7.  Amazon has them too.

 

[John61CT]

And a decent ammeter cost maybe $30, essential to managing any mobile electric system IMO.

One powering a fridge from an inverter is **much** more sophisticated and technically demanding than most, if you want reliability gotta up your game.

 

[nyyankees588]

Thanks everybody for the responses. Honestly, they have been super super helpful. I'll be picking up a ammeter and hydrometer when I get to the next town/city. The suggested voltage tests/monitoring makes sense to me.

Since checking and re-tightening the connections, the issues seem to have subsided, but it has only been 24hrs, so I'll definitely continue with the troubleshooting to ensure that my system is in good shape.

If anybody is in southern Utah or Colorado, let me know and I'll happily treat you to a drink/meal.

 

[John61CT]

If you want a clamp-type ammeter, decent for the price is "Uni-T UT203".

I doubt anything in B&M stores will be nearly as good value as online.

Best brand is Fluke, but pricey. I've been looking for the model I want used on eBay, but so far they don't go for under $250

 

[tx2sturgis]

 

[nyyankees588]

So it's been a few days now and after tightening all of the connections, everything is running perfectly. I can hardly believe it was that easy/feel slightly like a dumby, but am super happy that it worked out. Thanks for all of the pointers and help. I also bought a ammeter and battery hydrometer and everything checks out fine. Lesson learned to always ensure connections are rock solid. Onwards and upwards.

 

[tx2sturgis]

Where do I send the bill?

 

[HumbleBeginnings]

I guess I'll be checking my connections tonight... just in case.

 

[frater secessus]

Thanks for reporting back. It really is helpful for us and other folks who come by after us.