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Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 12:25am 10 Oct 2018
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For quite a while I have been thinking about how to fabricate some suitable metalwork to house my latest 5Kw inverter and battery + BMS. Not having access to suitable large sheet metal working equipment with such wonders as a wide guillotine or a pan brake, I came up with the idea of recycling bits and pieces from old filing cabinets.
These filing cabinets are cheap, maybe twenty or thirty dollars, and being mass produced on automated equipment, they are nice and square and accurate in construction. With a bit of imagination the various parts can be reassembled differently, or modified to make something quite different.
Anyhow here is my flip top inverter built into the outer shell of a two drawer filing cabinet.
Its built on a piece of 6mm steel plate with suitable heavy duty castors bolted underneath, and all the heavy magnetics bolted on top. Very easy to make, and very strong, and it supports the very light sheet metal of the filing cabinet which is inherently very flexy and weak, but the 6mm plate really stiffens it up.
The lid is bolted to a length of piano hinge, and uses a pair of gas struts to counterbalance the weight. At about the 45 degree point it is balanced, but beyond that it pops up by itself and locks in the up position.
It makes everything very easy to get too at a good working height. Plenty of light as well. Its now finished and has been working perfectly without a single problem for a couple of weeks.
The other half of the system is the battery box, BMS, and battery charger. Still putting all that together, only have the metalwork to show here so far. But all the electronics for it is complete and has been running for several months. The BMS has an XVGA video output which drives a 17 inch LCD monitor to indicate cell voltages on a histogram display.
At the moment I have thirty 50Ah Winston cells (100v 50Ah) which fit perfectly into a standard filing cabinet drawer with about 10mm clearance width wise, and 3mm clearance length wise. A completely removable lid will give pretty good access to that.
I can fit another thirty cells into the lower drawer, but don't yet know If I need that extra capacity. Will probably upgrade it one day. I have bolted a large bar bell weight at the back of the 6mm steel base plate to prevent the whole thing tipping forward when the lower drawer is pulled forward. Can fit a second barbell weight below the 6mm plate if necessary.
Pretty pleased with how these filing cabinets have turned out, and it only required very basic tools to do the whole job, and it can all be done without having any visible exposed screw heads.
Cheers, Tony.
Ralph2k6 Senior Member Joined: 24/09/2017 Location: AustraliaPosts: 129
Posted: 03:25am 10 Oct 2018
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Very nice work indeed. Will the lithium cells generate much heat while in use? Just wondering due to the confined space.Ralph
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 04:18am 10 Oct 2018
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Shouldn't think so, they will not be working very hard.
The inverter has been especially designed to work directly connected to the solar panels without needing a battery to stabilize the voltage.
The inverter sees no load dc input voltages up to 145v during the day. Only when the solar panel voltage falls lower than the 100v battery will the battery begin to discharge.
During the day the batteries see no more than a steady constant ten amp charge without any discharge at all except during really gloomy days.
At night the typical inverter load here is less than about 150 watts, or maybe two battery amps max. So the batteries are always very lightly loaded and should not see any significant heating.
Its not like a conventional heavily loaded 48v system where there could be up to 100 amps constantly shuffling in and out of the battery during the day. The whole system operates in a very different mode, to place the least possible stress on the batteries.Edited by Warpspeed 2018-10-11Cheers, Tony.
Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1026
Posted: 09:00am 10 Oct 2018
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That looks very neat and tidy, And I think they are the most powerful set of filing cabinets that I have seen yet. Cheers Aaron Off The Grid
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 09:06am 10 Oct 2018
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And good for you if you can do that. With my lithiums there are indeed very heavy currents shuffling and the cells need to be very strongly clamped together - I use a steel RHS at each end with allthread clamping - or they will bow out (get fatter) which is not reversible.
Your ingenious cabinet is very impressive Tony. Klaus
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 09:14am 10 Oct 2018
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Klaus, I do have 10mm extra gap down the sides and I can always add a couple f compression plates down the sides held together with all thread. I will see if the cells start to warm up in use, if so I will take your advice.
It should be fairly simple to build an Oz type of inverter into something like this.
The tunnel type of heatsink construction would be vertical with the lid closed.
With the lid open the main circuit board becomes horizontal, and you can walk right around it to work on either side with really good access and visibility at a nice working height standing up. A bar stool would also be about right.
The heavy flat steel base plate and castors are perfect for supporting the very heavy toroid and choke, and the whole thing can be wheeled neatly under a workbench.
Its so very simple to make, just a few holes in a flat plate, some nuts and bolts, a couple of gas struts, a long hinge, and if you are lucky no painting either except perhaps for the base plate.Edited by Warpspeed 2018-10-11Cheers, Tony.
renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678
Posted: 09:18am 10 Oct 2018
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That's a ripper setup Warp, my small space needs something slim(ish) mounted to a wall though.
Good to hear your new machine is going so well. So you should be totally off grid when the batt draw is finished yeah? You already have a couple of backup inverters.Cheers Caveman Mark Off grid eastern Melb
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 09:22am 10 Oct 2018
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Yup, its running right now. Direct off the solar panels during the day, and works off a grid powered three phase rectifier at night, or during extreme cloud.
Once the battery box, charger, and BMS are completely wired up I will be off grid.
All the video and BMS has been working for about a year, just could not decide what to do with the batteries.
These filing cabinets are so cheap and available, that its worth getting a couple to pull to bits and play around with. They are not all the same, the construction has some subtle and not so subtle differences. Once you get into it, you will then know exactly what to look out for when choosing the next victim filing cabinet.
The filing cabinet for the battery box is actually upside down. What was the original 100mm wide kick plate is now at the top to house the circuit breaker and panel meters.Edited by Warpspeed 2018-10-11Cheers, Tony.
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 10:15am 10 Oct 2018
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Tony, can you do me a favor please? I have been trying to send you a PM a couple of times but it disappeared. I have just figured out now it was rejected since your mailbox is full . I wish the forum would save a draft in such cases as its a pain to have to type the message out again and there is no pre warning the message will be lost when attempting to post it since one does not know about the full PM box.
Can you fix that Gizmo? Challenge for the day perhaps .Klaus
Ralph2k6 Senior Member Joined: 24/09/2017 Location: AustraliaPosts: 129
Posted: 11:17am 10 Oct 2018
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Tinker. I know it won't help now, but for me when I'm on the PC I often copy and paste just in case. Some sites can also have timer limits that kick in and scrap what you've written AFTER you press 'post'
Sorry Warp, off topic.Edited by Ralph2k6 2018-10-11Ralph
johnmc Senior Member Joined: 21/01/2011 Location: AustraliaPosts: 282
Posted: 11:25am 10 Oct 2018
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Warp, that is a smart looking bit of gear.
cheers johnjohnmc
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 08:29pm 10 Oct 2018
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Klaus, my in box is now completely empty.
This is what I had before, two 6mm steel plates clamped either side. The problem with that is that the cells fit so snugly into a filing cabinet drawer that the only place to put the all thread is underneath and across the top of the cells.
With a sliding drawer it all becomes very cramped for height as the cells need to be raised by about 10mm for the all thread to pass underneath. I did insulate the upper all thread with neoprene hose to prevent accidental short circuits.
I could still do it into the upper battery compartment as there is plenty of height available up there. But fitting the lower all thread and nuts would be a horrible job. I never had any battery overheating problems before, so will try the batteries loose and keep an eye on the battery temperature.
There is a shunt trip on the 63 amp battery isolation circuit breaker for last resort protection of undervoltage and overvoltage. I could also trip the breaker from a battery over temperature sensor. Will see how it all goes first before adding more complexity and inconvenience. Edited by Warpspeed 2018-10-12Cheers, Tony.
yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166
Posted: 03:22am 11 Oct 2018
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Hi Tony, one of my favorite builds is to house the battery bank inside a work bench with a removable or tilting top very similar to your concept.
I quite often use a banding tool and band the cells with 2-3 hoops in a 3,4,6 or 8 cell group with stainless bands. It would be better with end plates under the bands but I haven't fitted too many with them.
from memory its a tridon 16mm band.
I gave up on solid cell links and went to braid, getting everything on the post perfectly clean and flat and tight and torqued can be tricky. I have had a couple where I cant tell if I am flexing the link or stripping the thread in the post I'm confused, no wait... maybe I'm not...
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 03:49am 11 Oct 2018
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Klaus
renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678
Posted: 04:02am 11 Oct 2018
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Hahahahaha trust you to pull one apart Klaus, I'm surprised you didn't try and fix it and put it all back together.Edited by renewableMark 2018-10-12Cheers Caveman Mark Off grid eastern Melb
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 04:50am 11 Oct 2018
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Yes Mark, I have been known to take brand new things apart just to see what makes them tick , must be something in my genes...
Those lithium cells are rather difficult to open up - a shallow circular saw cut did the trick - and the plates/separators are extremely tightly packed. You would not even think of putting it back seeing that.Klaus
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 06:44am 11 Oct 2018
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[quote]You are game placing any rods across the top of those batteries - I have them at the side of the stack.[/quote]
Its actually not too bad, the rods are insulated and well out of the way. I cannot fit them anywhere else.
The cells are raised up on 10mm treated pine fence palings to clear the lower rods. Thinking about it, I can insert these lower rods from the top and fit the nuts on the ends from underneath. As I already have all the parts I may give it a go. The original problem of insufficient clearance at the top within a sliding drawer does not apply to my upper battery compartment.Cheers, Tony.
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 09:27am 11 Oct 2018
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I see now, the rods are not on top but in between the cells, looks good. Interesting to see your battery cell arrangement, I have mine alternating + and - so the links are straight across. Are those home made spacers you fit that PCB onto?
Did you have to beef up the drawer slides to take the battery load? That filing cabinet idea looks better the more I think about it, certainly worth while to look into for the cabinet challenged and I dare say it has heaps more room than the Aerosharp enclosure squeeze fit.Klaus
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 07:08pm 11 Oct 2018
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All the cells have the same orientation, as do the circuit boards which makes them easier to interconnect both to each other and the multiplexing drive which selects which cell is being monitored by the BMS.
The smaller 50Ah Winston cells are unique in having M6 threads, and a threaded stud was screwed into each battery terminal never to be removed. That preserves the thread into the fragile aluminium battery terminal, and I can fit and remove the M6 nuts dozens of times without any worries about stripping threads through over tightening, or cross threading. Also the studs go right down to the bottom of the thread and will be more robust than a short bolt that only uses part of the female thread length.
The circuit boards require spacers to clear the hump in the middle of the cell which sticks up a fair way. The crimp lugs for the interconnecting cables plus five steel washers are needed to gain sufficient height.
This thirty cell arrangement produces 100 nominal volts, but the same cells could be paired to produce 50 nominal volts. The 50Ah Winstons are the only size that fits as well as they do into a standard filing cabinet. Trev was mystified why I only ordered thirty cells instead of the usual thirty two. The secret is now revealed.
Ancient filing cabinets use skinny plastic wheels with pin bearings in the slides which are usually worn out or damaged and are best avoided. More recent filing cabinets use greased steel balls which make beautiful really heavy duty slides, and are easily up to the job of supporting a 75Kg battery. A filing cabinet stuffed full of paper would probably weigh almost that much anyway.
These more modern filing cabinets use a single piece of steel for the outer shell bent into a U shape with back and two sides. Dimensions are fairly standard but do vary slightly. The sides might be 610 x 680 and the front 465 x 680. Look for this single piece construction, as some filing cabinets, even the modern ones have three piece outer shells which are physically much weaker and don't look quite so nice.
Edited by Warpspeed 2018-10-13Cheers, Tony.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 08:37pm 11 Oct 2018
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I have had several goes at this filing cabinet game, and have discovered quite a few (now) very obvious things the hard way.
My first attempt was just to fill a lower filing cabinet drawer with batteries and maybe fit the inverter somehow to the upper drawer. I soon discovered that sliding out the lower drawer just caused the whole mess to tilt dangerously forwards, with no obvious way to fix the problem.
Attempt number two was to mount the filing cabinet drawer onto a 6mm steel plate with castors, and cut away the lower section of the filing cabinet, so I could "park" my new battery trolley into its "garage". That worked, but it was an ugly solution I was never happy with.
Attempt three is what I now have. The batteries stay in the cabinet with top access to fix the tilting forward problem. As long as those top batteries stay where they are, with the assistance of some additional ballast weight placed right at the back, a lower sliding drawer full of batteries then becomes possible.Edited by Warpspeed 2018-10-13Cheers, Tony.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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