Author Topic: Dead AGM Batteries  (Read 950 times)

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Offline OTG

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Dead AGM Batteries
« on: January 27, 2019, 12:07:27 am »
So I took the "solar truck" out this morning to cut up a downed tree with the electric chainsaw (MK Triton single-cab with 3 x 36V 190W panels mounted in parallel atop the tray canopy, feeding a Mastervolt 20A PWM Charge Controller, 2 x 120AH 12V AGM Deep Cycle batteries in series for 24V, and a PowerJack 5kW Inverter - all about 3years old now).

The inverter powered up as usual, I went to run the chainsaw, and... nothing!  ??? I checked the Controller and it's LCD screen is indicating that the battery has "high resistance" and I now realise:
1. the only thing powering the inverter was the solar array (hence it conked out when the load came on), and more importantly...
2. somethin's goin' on very wrong with my batteries!  :P

So after a day out with the trusty old Stihl, I've just done a quick Voltage test and both batteries are reading OL (Overload).

I've never had a dead battery do this (usually it's just EOL/under-voltage) and I couldn't find anything on the Google machine about such a reading, so I figured I'd ask the electrickery whizzes here:

1. Whats likely wrong with these batteries?
2. What likely caused the fault/failure?
3. Any chance of resurrecting them?

Like I said they're about 3 years old and have had a reasonably easy life thus far (they only get used occasionally (always on sunny days) for DC Welding, Chainsawing, running a small cement mixer, etc...). They are cheaper no-name batteries, but still, I expected to get more out of them then I have.

Any thoughts/help/advice appreciated.

Offline WooferHound

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Re: Dead AGM Batteries
« Reply #1 on: January 27, 2019, 10:58:11 am »
You have 125 amphours in batteries
If the chainsaw uses 10 amps at 120 volts, then the inverter will pull 110 amps from the battery
This is not very healthy for the batteries
For long life you should keep the voltage above 11.8 volts
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Offline Pete

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Re: Dead AGM Batteries
« Reply #2 on: January 27, 2019, 02:34:52 pm »
My suggestion is that you have a high resistance joint on the battery connections or a loose connection somewhere. You said that the batteries are reading Overload. Not sure if you meant to say Overvoltage or not.
Anyway with a high resistance joint on the battery terminals , you would be reading overvoltage because you would be reading solar panel voltage not battery voltage. Also you would not be able to draw much current from the batteries because of the crook terminals.
So clean the battery terminals well.
Use some battery terminal spray to prevent corrosion
And get back to us with what you find
cheerio and good luck
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Offline MadScientist267

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Re: Dead AGM Batteries
« Reply #3 on: January 27, 2019, 06:46:54 pm »
I'm not even sure where to begin here.

1. Yes, for deep cycle, around the 1C rate (120A; I'll get back to this in a sec)... they put up with it for short periods... But this is just bad juju. My guess is that they're at the very least hybrid "marine/RV" deep cycle/cranking batteries...

2. Chainsaw is going to be a series wound motor, and working it's way up to if not at or even beyond whole horsepower... Which by definition (ignoring efficiency of the motor itself just for the moment, which just compounds the issue) is ~750W per HP. With starting surges being many many times this. At 1HP your running load amperage (again ignoring additional inefficiency of the inverter) at 24V is 31.25A. That's ~C/4 for the battery in question, still rather bad juju for anything with "deep cycle" in it's title. Then add the conversion losses that the inverter and motor bring in.

3. Woof, where's the "110A" come from? This is one of those "1 dimensional equations" you got going on there... O.o

4. "OL" is something meters with probes generally display and indicate one of 2 things... "Overload" or "Open Loop" (the latter applying to continuity). Either way, if you're seeing this on a standard multimeter with 24V worth of battery, "you're going it wrong" is the first thing that comes to mind. Either its not set to measure the right range of voltage, or not set to measure voltage at all.

5. Again ignoring some efficiency considerations, you're feeding the bank with a "label" of 570W. This means that you're theoretically capable of putting nearly *2C* charge rate into the battery at high noon on a clear day. This is insane. Just be glad you aren't using an MPPT controller... With plain PWM, because of how it's able to use the PV, you're probably a little under this at worst case, and then on this side of the coin, inefficiency is "working in your favor" by reducing that even more. [EDIT - Future readers: I really hosed this call up somehow lol - Addressed the correction in the reply below]

6. The other thing you mention is welding with these. "Please say it isn't so"... Yes it is *possible* to weld using batteries, but even ignoring everything else that needs to be taken into consideration with this (series inductance etc)... This isn't something I'd even remotely be considering with this size battery. You're begging for an "event".

Lead acid is forgiving, but it has its limits. I apologize if I'm assuming too much here but what I've read in both the OP and parts of replies so far, stood my hair up. What's described isn't a "large system" by any stretch, but you're still messing with just enough power to get yourself into a lot of trouble if something goes wrong.

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Offline OTG

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Re: Dead AGM Batteries
« Reply #4 on: January 28, 2019, 12:14:11 am »
Thanks guys!

Ok... after more testing today, turns out the Voltmeter on my Digitech Clampmeter is on the fritz, hence the strange "OL" Voltage reading. I found if I waited about 10secs after taking the probes off the terminals you can see the V reading come back down into range, with readings starting from about 5000V as it scales down, per the pic)! So yeah, this POS meter was hardly helping my efforts figuring this out! >:(

Using a working Multimeter today, I found the battery voltages are reading fine (with the Panels/Controller isolated), each battery returning 13.06V/13.04V respectively. In series all looks good too, returning 26.10V.

However, the moment you try to feed/drain the batteries the Charge Controller/Inverter protest in their respective ways -
a. Charge Controller manual describes the displayed Error as follows - "Battery wires or battery fuse damaged, battery has high resistance - Check battery wires, fuses and battery". Even with this error, the Controller does actually continue to trickle in charge (about 1.6A) however.
b. The Inverter's display does function (per the pic), but whatever current is trickling through, it's not enough to produce any power.

So I've checked the wiring, breakers, cleaned up the terminals, checked all terminations, but the issue persists. The only thing I haven't done is try to pull a DC load directly from the batteries (like DC welding... don't freak out just yet MadScientist267!  :D ).

The problem as crudely as I can explain it is - the batteries have good voltage, but can't supply current - for whatever reason!? Any further thoughts much appreciated!

Now, MadScientist...

Thanks for the detailed reply - I'm interested in better understanding your "hair standing on end concerns"  :o oh ooohh  ;). A lot of your assessment was spot on!!! The Chainsaw is about 750W (31A DC @ 24V) and the welder (a DC Mig Readywelder) pulls about 200A DC. These batteries, if I recall correctly, have a max discharge rating of about 1000A (5s). So I'm within that spec, but to your point C ratings are another matter, and so I keep the welding to small "bush welding" jobs (seconds of welding) and chainsawing/jackhammering/etc... jobs to minutes (10/15/20max) - basically, if the Controller gives me the 75% DOD beep, I stop. So (from my perspective at least) the usage hasn't been too rough - or am I being overly optimistic?

And per point 5. can you elaborate on whats so insane about this theoretical charge rate? I'm not following and would like to better understand. Shouldn't the CC (be it PWM or MPPT) prevent any charging "insanity"? ::) (obviously depending on the units features (e.g. reverse polarity detection) and the array being within spec of the unit (i.e. nominal PV voltage, etc...)

And per point 6., the "event" you're referring to I assume could be summarised as batteries going "boom"? :P Per above, DC or "bush" welding is a pretty common thing, I'm within the max discharge rating of the batteries, try to go easy on them with each job, and I've done a bunch of it to date with nary an issue. So again if you could elaborate on what kind of event/s and what circumstances might lead to one, that would be greatly appreciated.

Thanks again guys, all your thoughts/insights/experiences are greatly appreciated.


Offline MadScientist267

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Re: Dead AGM Batteries
« Reply #5 on: January 28, 2019, 02:34:39 pm »
Sounds like the meter definitely took a dump and that certainly explains that end of it.

Battery voltage "normal" under no load but unable to supply current is symptomatic of a damaged cell in the battery somewhere if all of the connections and wiring check out. More than likely what you'll find is that under load, one will still be trying to hold it's end up, while the other one goes silly, possibly even completely "mirroring" the good one with an inverse voltage across it's terminals.

I wouldn't use the electronics present to try and test for these conditions because the unpredictability could cause damage to the electronics themselves.

Rather, disconnect everything from both batteries and give them a simple moderate load such as a headlight across each one independently and see if it can hold it up, and what the terminal voltage is while it's doing so. The one with the issue should reveal itself by not providing enough power (or any at all from the sound of it) to light the headlight up, and the meter will confirm the degree of the sag.

On to the cause from how I perceive it...

I think they serve a rough life as 75% down is pretty significant for lead acid, and while there are many factors that contribute to cell damage in batteries, they're not all "equal". You're in a portable environment there for one. Discharged cells are more fragile and while AGM is physically more rigid in construction, they are still susceptible to vibration and shock... The lower the SoC, the more pronounced this is. There's a good chance there's a crack in the internal electrical structure somewhere in a cell, which because they're all in series, the limitations of the weakest cell affects the entire battery.

I screwed up somehow with the math on the theoretical "2C charging rate"... Crossed the streams... Lol I was tired when I was writing that... But you're still looking at C/5... and this is still another strong potential factor because it exacerbates even minor differences in cells (unavoidable), which leads to runaway imbalance. Weaker cells will reach both charged and discharged states sooner than the stronger ones, which ages them quicker yet because they spend more time at both ends. Sealed cells are particularly vulnerable to overcharge as excess gassing causes pressure to build, and even tho some have catalytic recombination devices in them (to turn hydrogen and oxygen back into water), these can easily be overwhelmed by excessive rate... And unlike in a flooded cell, once it's lost, the water is gone forever.

Extreme rates also can cause warping and buckling of plates due to expansion from hot spots that form... Not only leading to cracking but even internal shorts... I probably don't need to explain where that can lead...

However since you asked, yes an "event" would refer to, worst case, catastrophic failure of a cell... Explosion, etc... Best case, internal damage resulting in a shorted cell that essentially is just "bypassing" itself... And anything in between. In any case, the early demise of the cell in question, and by extension, the battery it's part of.

Charge rates need to be limited to allow the chemical reactions in the cells to be able to keep up with the current flow causing them to happen. This is what the "absorb" stage is about in charge controllers. The current is allowed to taper off while the voltage is held steady because as the cells reach full, the number of places these reactions can occur become less and less, and the places where they've taken place in full, the energy gets expended splitting water, making heat, and causing other unwanted reactions that slowly but permanently degrade [namely positive] plate material.

Typically, lead acid is designed for C/10 charging rates, and while some excursion above this can be tolerated, and in some cases even designed in for a specific battery's purpose, higher than this is generally not a good thing.

So while you're not looking at 2C (which would be *20 times* this "standard rate"!), C/5 is still very high to be using regularly. If the controller has means to limit (it may not, being only PWM), you may want to consider dialing it back some to limit those peaks. Unfortunately, this is of course a double sided coin... The controller doesn't know the difference between the battery and an ongoing external load... So its a balance. With the whole "2C" thing behind us, which I again apologize for... Sigh... You may be able to just "ignore" that for your use case. Just keep it in mind for general purposes.

Discharge rates are a little different because the source of the energy is the battery itself and there's a degree of self limiting that occurs, but it still can be problematic. Depending on the physical construction of the plates and cells, the rate is limited by some intentional combination of the plates and the electrolyte, with the battery's intended purpose in mind. Also, during discharge, gassing is *much* less a factor and so more of the plate area stays in contact with the electrolyte, helping reduce localized hot spots by way of improved cooling. The reaction during discharge is also endothermic (you'll never notice the cooling effect however because ohmic heating overtakes it).

In a battery that's meant to crank an engine, capacity limitation is imposed by the plates, with an "excess of acid" (relative to plate mass), as they're designed to deliver a lot of current for a short period and then be immediately recharged.

Deep cycle has much more plate than acid relative to a cranking battery but with a lower instantaneous surface area in contact with the electrolyte, since peak current delivery isn't as important as the ability to deliver power over long periods of time. This reduction in active area increases the internal resistance of the cells however, so when an attempt to draw large amounts of current from a deep cycle cell takes place (relative to the cell capacity), it generates more heat, which just as in charging, can result in plate warping and other identical threats that too high a rate can cause there.

The so called "Marine/RV" batteries are a hybrid between these two extremes, and for anything outside of small light loads (again relative to the capacity) for comparatively short periods, and starting smaller engines (outboards, generators etc), they're generally considered "not great at either one". They can't deliver quite the punch that a "true" cranking battery can for rolling an engine over in the cold, and they don't stand up to the deeper cycling as well as a true deep cycle can either. This doesn't mean they don't have their uses, they do, but it's a bit more limited than it would appear, and so they endure a little more abuse overall by being selected for jobs they're not particularly suited for. The price tag is usually the alluring factor...

Hope this helps some... I know it was a little drawn out, but figured I'd go ahead and cover all the bases on this one. These "little black boxes" we all rely on are a lot more complicated than they'd appear on the surface, unfortunately.

One other thing comes to mind with the advent of the pics... That's a pretty simple and clean layout... But other than the jumper, the wire sizes there look a little anemic for the loads you're saying are in use... May want to look into beefing them up a little... To reduce losses even if they're holding up safety wise.

Steve
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Offline lighthunter

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Re: Dead AGM Batteries
« Reply #6 on: February 02, 2019, 03:19:51 pm »
Defenitely an interesting problem you have. If the solution wasnt found in a bad connection, it is possible for an AGM to have a severed connection inside the battery case. It actually happens quite a bit with the jump starter packs. They demand so much current from a tiny battery that something gives. Ive never taken one apart but its possible they design them with a one-time fusible link of sorts or something just goes wrong with the connection, im not sure. One way to make trblshoot easy, use 4 alligator clip type jumper wires and attach a tiny (automotive bulb) across each agm. This will give you a voltage indication of each battery under load. Let us know how it goes, sounds fun!  :)

BTW, i like your setup, good idea! I may have to do that for the lighter work, take some hours off the stihl and easier on my body than limb work with an ms391.
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Offline OTG

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Re: Dead AGM Batteries
« Reply #7 on: February 05, 2019, 02:37:54 am »
Thanks MS267,

With my head screwed back on (I had "$#!+-to-do" that weekend and the compounding failures honestly threw me a bit off-kilter - I also lost my Stihl air filter, so I had to improvise with a rag, a real PITA morning...) I did some more comprehensive testing last weekend and the picture is much clearer now...

The meter is basically cactus - V readings are wonk... sometimes right (especially at lower V like AA batteries, or when flicking between Auto/Manual ranges) but mostly wrong (and all over the place); Cap & Temp readings are bung (all 0.00); but A and Resistance are OK (hooray). Pity... it's only 4 years old and has been a relative "Garage Queen" of a meter. Spose I'll just use it for cl-Amp meter duties now...

I tested each battery with a small 12V 1.5A Flood Light, and as you guessed again (do you play a lot of Charades or something!? ;) ) one battery was fine under load, the other's V went from a steady 13V, to erratic/constantly changing readings (as low as a few V, high as about 80V and everything in-between) with the light constantly dimming in and out. So I have a buggered battery - what do you think these symptoms indicate - damaged cell or two?

I hooked up some car batteries to test the CC and Panels (individually & together) and the V/A of these components all look ok - so I don't think they're part of the problem.

And yep, fair cop on the DoD point - the (silly) reason for it is the CC gives an audible alarm at 75%/50%/25% (fixed/not user-programmable), so it was just an easy marker to tool-down on the bigger jobs/with longer use. Low SoC/vibrations & shock could well be a factor too, as the pattern of use is basically drive somewhere, do the work, drive back - often via a bumpy track (not to mention, the old 4M40 Diesel comes to a pretty rough stop when you cut the ignition :P ). A definite lesson learned and I'll be changing my max-DoD behaviours. The terrain I can't do much about, I'll just keep taking it easy on the rough stuff.

Thanks for clearing up the charge rates (no biggie!!!  :D ) and the detailed explainer was definitely of help. Indeed, as "Marine/RV" hybrids I'll be more mindful of their limitations in future.

RE the wiring - it's standard 4mm Solar Power Cable (60A Max) and 0 Gauge Power Cable (proper tinned stuff - 300A Max) - so definitely safe/within-spec but to your point I'll throw in a second run of power cable in-between the batteries to further support the heavier loads.

Indeed, these "little black boxes" do just-work (the good kind :-) ) "like magic", and so we usually take them for granted - particularly the less electrickerally minded folks like myself.

Thanks again MS267!

Offline OTG

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Re: Dead AGM Batteries
« Reply #8 on: February 05, 2019, 02:57:31 am »
And thanks guys, I've been pretty happy with the "Solar Truck" so far (minus this battery hiccup).

I've got a bit of tough ground to cover (basalt country) and lots to do (fencing, remote infrastructure, clearing weeds (big cactus/lantana), more fencing, etc). I didn't want to lug around a genny and I hate having them constantly running for intermittent work (e.g. welding/jackhammering), and so the Solar Truck was born.

It's basically an old Meter Box, with 40mm Angle Bar welded on each side for mounting over the rear-view window (it was broken so I replaced with a flat sheet of colorbond), with an MDF offcut bolted inside holding the CC, Array/Battery CB's, and DC Loads fuses/bus bars for the Cigarrette Lighter outlet on the side (I use this for worklights now and then, charging phones, etc...). I used 50A Anderson plugs to terminate the battery/solar leads for easy removal/swapping of bits if need be (this has actually come in REAL handy at times - using additional leads, I can charge car batteries off the array and I also used the array for a while to run my Solar Bore Pump while I was still getting it's permanent panel in place (we needed the water, damn drought!)). The Dual Battery box is just some 75x75 4mm (I think) SHS cut up, glued together, and bolted to the tray. The array is mounted on 25mm SHS/40mm Angle bar, cut/glued flush together to easily slide the panels on from the back. Cables enter the tray via the ABS Cable Entry Glands. The inverter I keep in the shed and it sit's on the breadcrate when in use, held in place by the bit of broken tie-down strap (I was going to make a mount but haven't got around to it yet). I had cut the head of a SS bolt, and used two seperate nuts for the Solar/Inverter Cables, so I could easily take off the inverter without touching the solar terminations. That's a longwinded brain dump, but that's about it...

Other then some Sikaflex, the Cable Gland, and the Electrickery components, the rest was cobbled together from offcuts and freebies - so it worked out pretty cheap in the end.

My main concern was panel damage (e.g. cell cracks, interconnect breakages, etc...) but so far so good. Also the truck lives outside, so I'm mindful to park at an angle for water run-off on the panels and when using it, I also park for maximum solar gain (especially considering the panels lay flat).

If I could turn back time and magic up an old trailer frame I might have rigged it all up on that, which would free the truck up for less 'considerate' driving. But I can't do either and so Solar Truck it is... which really has been invaluable so far and allowed me to get lots done, genny/dinosaur juice free (not counting the truck itself)! Also, as good as the MS250 is, I very much loathe the 2 Stroke fumes, not to mention fueling it up and all for mostly small jobs. I've very much enjoyed using the corded electric one and not smelling like an old lawn-mower at the end of it. Plus it's much easier to swing around. And your 391's probably twice the chainsaw mine is lighthunter - I can imagine ti would be a real lump for limb work!  :D

Also I'm not sure about the battery one-time fusible links... if anybody else out there knows It'd be interesting to hear.

Otherwise, I'll be grabbing new batteries shortly and will have the truck back to work in no time!


Offline MadScientist267

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Re: Dead AGM Batteries
« Reply #9 on: February 05, 2019, 09:16:55 am »
It's a nice looking setup OTG... And would seem to do the job for the most part exactly as you need it to, which is what matters the most.

As for the charades... Haha Naa. Just had and otherwise seen my fair share of battery failures over time, not the least of which was my rig recently. There's a bunch of things that pull in polar opposite directions when the mobile thing gets involved... And it becomes a "best balance" situation to try and keep everything happy.

Batteries being what they are, heart of any system and finicky about what they need... Tend to take a lot of hits and sometimes there's just a "to be expected" factor. Rough and tumble environment is certainly one contributor.

The panels on the other hand, they're surprisingly robust in that service ain't they? Lol I remember thinking I needed to protect mine in all kinds of ways and feared for quite a while that they'd suffer damage from this and that... But while I wouldn't go out of my way to abuse them, they do stand up to quite a bit.

Out of curiosity, what mounting scheme did you use for them? I only ask because I chose a "floating" system and just kinda wanted to compare notes. Simple as it turned out, it was one of the most thought provoking aspects of my entire design and I was always curious what others come up with for the unique aspects that mobile brings to the table.
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Offline OTG

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Re: Dead AGM Batteries
« Reply #10 on: February 17, 2019, 12:38:34 am »
Yeah exactly - it meets 99.9% of my needs, and that's what matters. I've ordered a couple of 12V 170Ah Batt's, which should give me that bit of extra headroom so I'm not draining them so much anymore.

And yeah, mobile throws all sorts of other spanners in the works... particularly wrt the array. Though as you noted (and similarly to my initial fears and subsequent surprise) the panels have held up very well indeed. When putting this whole thing together  the array was the bit I'd think about laying in bed at night (how best to do it - without breaking the bank... or panels :) ).

For me, the first consideration was ventilation... how to get adequate air under them, without causing too much drag/uplift whilst driving. Hence I used the 25mm SHS to lift the array off the aluminium roof, whilst also supporting the long side of the panels too (and with the 40mm angle iron on the short side, all four sides of the panel frames are supported). The one exception here is the front panel, who's front side hangs slightly over the cab (per the middle pic above). It's hung forward of the tray to avoid rear kocks to the back panel/array frame, and to have this unsupported side in the middle of the truck so it's less affected by bumps and what not.

I think I had a similar idea to you with having some "spring" in the array frame. (Fortunately in a sense) the tray cab at some stage in it's life prior to me copped a whack from the back, which put a slight concave into it lengthwise (that silver square is me patching a related hole in the roof). This mean't my array actually "floats" in the middle by maybe 5mm or so - the two middle lenghts of 25mm SHS aren't actually in contact with the roof (only the ends are bolted down), and the frame flexes slightly at these two points, so with a slight gap either side of the middle panel (to prevent the panel frames rubbing) the whole thing can flex a bit on the bumps (a bit like a leaf spring). And to absorb some shock, each contact point with the roof (both the bolted and floating points) has a bit of EPDM Rubber strip under it.

It all seems to have worked alright thus far  :P - fingers crossed it stays that way.  ;D

Likewise, I'd be curious to hear how you went about it with your rig.

Offline MadScientist267

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Re: Dead AGM Batteries
« Reply #11 on: February 17, 2019, 09:55:30 pm »
Not bad, sounds like it works.

With mine I used 4 angle aluminum brackets per panel, which slide up under retaining clips... They're staggered in such a way that they interleave in the center, the whole array riding on 3 rails made of channel aluminum spanning the entire roof from front to back.

The panels are not firmly restrained in any way, and are only suspended by "PVC rubber" underlayment material, allowing them to shift as the box flexes from bumps going down the road. This acts mostly as a "lubricant" to prevent metal on metal wear.

They're locked in place by keying clips that prevent them from sliding out from under the retainers, but can be removed if necessary for some reason. The lock clip details were intentionally left out of the original pics for security reasons, but in this pic, you can see how the suspension retainer scheme is set up...

8062-0

Fully assembled, any panel can be removed individually without disturbing the others.

The main story on how all this comes together is in this thread.

It was definitely fun to come up with and implement the design, but it did indeed serve very well in the end and I never had any installation related issues come up after launch.
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Offline Pete

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Re: Dead AGM Batteries
« Reply #12 on: February 18, 2019, 03:13:50 pm »
Hi OTG you asked about fusible links. Not sure where you are but Jaycar have fuses that go up to 250 amps. They are pretty cheap and just bolt into a holder with two allen head screws. I use them on my stand alone system. In the event of an accidental short the batteries and cables won't go up in smoke. I have blown a couple of fuses using a heat gun run off my inverter. I found that I had a bad connection on one of my brass links. Fixed that no problems now.
As far as the meter goes, you could always take it apart and see if the switch is operating properly.
Some multimeters have pretty cheesy tracks on the circuit board that the switch operates on. Cleaning up the circuit board can sometimes bring them back to life.
I have killed a few cheap multimeters by measuring high voltage DC ( which they were supposed to handle) on Valve amplifiers. Basically the tracks are too close together and the sparks jump across them and blow the meter up.
It is odd that your meter reads so erraticaly  on your load tests. A 1.5 amp load should not be a problem. Maybe you should also test the leads on your meter, they can easily break where they go into the plug or probe and give odd readings because of the high resistance.
Have fun,
Pete