Portable energy storage system

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  • benjaminbenjamin Solar Expert Posts: 34
    Re: Portable energy storage system

    I have only been able to find Tempered Low Iron glass in 1/4" thick sheets. Great idea for the backing though. I was going to use ABS plastic, but I may now use a very thin piece of rubber/plastic material and aluminium, which will keep the cells cooler.

    :)

    EDIT: Maybe just coat the aluminium with some sort of insulative material to prevent shorts and/or current flow. I'll need to research that.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Portable energy storage system

    Personally I think the OP has done a good job covering all the bases for homemade solar panels. Clearly research and thought have gone into it. Whether or not it's economically viable is another issue, but only he can decide that because only he can put a $ value on his time, the learning experience, and how much he enjoys building them.

    The reason you will read a lot of cautions about Amperage is because even though a given component is rated for "X" Amps the closer it is run to that limit the shorter its lifespan will be*. You may have noticed wire has two different ratings: in conduit and in open air. It's all about heat, and the higher the Amps the more heat. If you ever looked at the test specs for rating things ... oh my! Talk about caveats! "X" Amps @ "Y" degrees for "Z" minutes on a mild day in December when there's no moon and the wind is blowing from the East at precisely 2.789 knots (test site elevation not to exceed 1,000 feet, relative humidity 46.3%). Okay that's just silly, but it demonstrates the fact that ratings are under specific conditions. Thus we have the rule of thumb "keep the Amperage as low as possible" in order to extend component life and reduce chances of nasty surprises. The fuse/breaker must always be the weakest link in the chain.

    *This is true of mechanical and structural components as well; run them closer to their limits and their lifespan is shortened.
  • icarusicarus Solar Expert Posts: 5,394 ✭✭✭✭
    Re: Portable energy storage system

    Taking Bill's suggestion to heart, I will not admonish further.

    My experience with home made panels is limited to what I see and read hear. For example, there was a thread here just a few weeks ago from someone who built a whole new array, only to have it not work as he expected. It was found to have numerous bad solder joints, corrosion on the wiring lugs etc.

    As for panel backing,, PVC or rubber/plastic is flammable.
    My problem with exposed buss bars is a function of having so much energized conductor out where a random drop of a screw driver or wrench can easily arc. Having blown up a battery once it is not something I would think anyone would want go through,, especially with the huge potential you have. (Mine was just a pick up battery) Being careful is important, but accidents happen!

    My issue with 12vdc has to do with the number of parallel connections with huge amperages in the total system. I am not suggesting that it cannot be made safe, I have merely suggested that a 24 or 48 vdc system might have suited you better, but we have had that discussion.

    Good luck (and that is a genuine wish!) and let us know how it goes.

    I will shut up now,

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 29,823 admin
    Re: Portable energy storage system

    I am not suggesting what your backing should be... I really don't know. However, I am not sure I would put aluminum in there... Possible electrical short issue and you may have thermal expansion issues too (differential expansion is a killer for life cycling).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 29,823 admin
    Re: Portable energy storage system

    By the way, I believe Tedar is the normal backing material for a solar panel. And I believe that EVA is typically used between the glass and the cell face (I don't know about the vendor--just a place to start).

    Again, just the little bit I know--I would not be able to tell you how to apply.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • benjaminbenjamin Solar Expert Posts: 34
    Re: Portable energy storage system

    I'll open up another thread for the Solar Panels. My main concern is matching the thermal expansion rates and protecting the cells. I have looked into the Tedar stuff and I'd really like to have a thicker backing.

    I went ahead and bought the crimping tool from Harbor Freight. I had to use a die grinder to make the dies big enough to crimp the wire. It's a heck of a workout to crimp 60 lugs.

    Also, I've built one of the bus bars and learned a few things. This isn't something one would normally want to do even if you have the tools. If you can buy one go ahead and do it because after the price of bolts, washers, locknuts etc you are only going to save $10-$30 per bus bar and they aren't fun to build. In my case I probably had no other option though because of the amperage it has to carry. (e.g I may have been able to find one for $2k or something, So I probably did save quite a bit on that). They will end up costing me about $45- $50 each. Use Grade 5 bolts if you ever build a bus bar yourself. I originally had grade 2 but one sheared off while I was screwing it into the bus bar. Forgive my non-technical terms here but this was do to twisting forces rather than stretching forces. Anyhow I don't know if the Grade 2 bolts would ever just happen to break once installed so I will be using Grade 5 from now on. The hardware store here also has Grade 8 but they run about 90 cents a piece and are probably much stronger than needed.
  • mike95490mike95490 Solar Expert Posts: 8,500 ✭✭✭✭✭
    Re: Portable energy storage system

    Bussbars are supposed to use COPPER bolts/hardware for the conductors. At work, we tap the bar with 10-24 threads (all the way through) and use no-ox goop on the connections and in the threads. Can't mix steel and copper, and with a steel bolt, you loose half your contact area.

    So maybe you are drilling thru holes, and using a nut on the backside ? best use 2, in a jam nut configuration in that case.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • benjaminbenjamin Solar Expert Posts: 34
    Re: Portable energy storage system

    I'm drilling the hole slightly smaller than the bolts and then spinning the bolt through the copper bar to create threads. They are nice and tight. They are configured as follows:

    1. Bolt
    2. Washer
    3. Bus Bar
    4. Lug
    5. Lock washer
    6. Nut

    Yes they are steel. Why can't you mix copper/steel?
  • loreleclorelec Solar Expert Posts: 200 ✭✭✭✭✭
    Re: Portable energy storage system

    I don't know of any problems mixing copper with steel bolts, but you should tap the holes before you try putting a bolt through them. Otherwise it's likely they'll seize and break, as you've found.

    Second thought, in an acidic environment (as you might have around your batteries), you shouldn't mix the two metals, as one will corrode the other.

    Marc
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Portable energy storage system

    the reason is galvanic reactions that may eat away at the 2 differing metals. if the bolts and washers you use normally could be stainless steel then this will work good for you. the steel bolt just use to cut threads somewhat.
  • BB.BB. Super Moderators, Administrators Posts: 29,823 admin
    Re: Portable energy storage system

    The other issue is steel (and usually stainless steels are worse) are relatively poor conductors relative to copper... So, with a steel bolt, most of the current only goes through the copper connections (reducing low resistance paths by 1/2).

    I guess you could look at copper bolts, but I have also seen and used brass bolts instead. Copper on copper bolts are probably going to gall and be "use once" connections. Brass on brass should be reusable and easier to find.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • benjaminbenjamin Solar Expert Posts: 34
    Re: Portable energy storage system

    I see.

    I've attached an image of the wires running from the batteries to the bus bars. This isn't wired up to the batteries yet, of course.
  • loreleclorelec Solar Expert Posts: 200 ✭✭✭✭✭
    Re: Portable energy storage system

    I'm pretty sure you need an electrolyte for a galvanic reaction to take place, which is why copper/steel water pipe unions are such a problem. If you can keep the bus bars dry (fumes from charging batteries won't help), then there probably isn't an issue. I also wouldn't worry about the resistivity differences between differing metals. The conductive path in one of those bolts is short, so my guess is that it would be a difference of micro-ohms.

    Marc
  • benjaminbenjamin Solar Expert Posts: 34
    Re: Portable energy storage system
    ajbelcher wrote: »
    Let me know if you need some of those big dc breakers - Usually have 1100 amp dc breakers - used as battery disconnects on telcomm systems / either available or coming available soon -

    Yes, I'll definitely need one, that would be great!

    I wired everything up temporarily for the purposes of testing. The AIMS inverter clearly isn't designed for 100% duty but it will meet my needs. I ran two 1,500W space heaters for two hours (On the AIMS). Everything performed flawlessly. All connections, wires and bus bars remained cold. The AIMS inverter did get nice and warm but appeared to be stable.

    I don't have any concerns about the Xantrex inverter or running them both simultaneously since they are wired separately.

    So I consider this a success. I should be good to go after adding fuses and breakers. Just for kicks, I'll test a 4500W load on the AIMS for 5-10 minutes or so.

    I used the Xantrex to recharge the bank. It had been in the 70s the last few days but last night it was 48F, so the Xantrex was feeding the batteries 14.8V and they all immediately started gassing. It sounded like an upside down waterfall or something. I set the battery temp to HOT which dropped the voltage down to 13.9-14.0V in order to fix this. I can tell that I will need a fan big enough to cycle all the air in the box every 10 seconds or so because if they start gassing heavily it won't be pretty should something spark. It will also need to be vented outside. I felt like it could easily exceed safe levels even in the garage. Regardless, I'll set the charging voltages low in order to avoid as much gassing as possible, so hopefully that was a one-time event.

    Also, the high amperage running through the (inverter) cables felt like water running through a garden hose. Pretty neat. What is the science behind being able to feel electricity running through a cable?
  • BB.BB. Super Moderators, Administrators Posts: 29,823 admin
    Re: Portable energy storage system

    My guess is that the high current flowing though the cables and 120 Hz from the inverter "modulating" the current... Each cable is generating a magnetic field with the cable next to it... So the cable have a 120 Hz push/pull going on between them (would feel a bit like a florescent light fixture "buzzing").

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • benjaminbenjamin Solar Expert Posts: 34
    Re: Portable energy storage system

    The total cost for this build, including hardware, fuses, breakers, batteries, inverters and everything will be under $5k.

    Just so you don't have to read through all the posts, here are the specs again.

    2100AH (25,200 Watt Hours) Capacity
    2500W Pure Sine (Xantrex 2.5 w/100A Charger)
    5000W Modified Sine (AIMS)
    -On Wheels

    My goal was to get the most AH capacity and W output per dollar spent. I think I did exceptionally well.
  • icarusicarus Solar Expert Posts: 5,394 ✭✭✭✭
    Re: Portable energy storage system

    If memory serves, gassing voltage starts ~2.3 volts per cell, or ~13.8 vdc, so they will gas even at your lower set voltage. Be very careful with the large number of cells in any enclosed space, and nearly any charging voltage(s)

    T
  • benjaminbenjamin Solar Expert Posts: 34
    Re: Portable energy storage system

    There's a chart about 1/3rd down that shows the gassing voltages based on temperature. No clue how accurate this one is, I'd like to find another one, or make my own...

    http://www.powerstream.com/SLA.htm
  • mike95490mike95490 Solar Expert Posts: 8,500 ✭✭✭✭✭
    Re: Portable energy storage system
    ....Yes they are steel. Why can't you mix copper/steel?


    Steel has a higher resistance than copper, so your bolt will be unable to share much of the current, thus forcing most of the current thru the "not so flat" interface between the lug and bussbar. enough current, and a couple years of time, the excess heat (at least copper bussbars spread the heat around well) causes more corrosion at the joint, causing more heat. Copper bolts, even though they dont' torque as tight, share the current better.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • monolocomonoloco Solar Expert Posts: 103 ✭✭
    Re: Portable energy storage system

    I can't see in your photos that the buss bars are insulated from the wood. If they are not you might want to consider that wood absorbs moisture and could conduct between the buss bars.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Portable energy storage system
    monoloco wrote: »
    I can't see in your photos that the buss bars are insulated from the wood. If they are not you might want to consider that wood absorbs moisture and could conduct between the buss bars.

    that's nothing that a good polyurethane coating couldn't cure.
  • mike95490mike95490 Solar Expert Posts: 8,500 ✭✭✭✭✭
    Re: Portable energy storage system

    From the photos, I can't see how thick the buss bars are, but they are pretty well "swiss cheesed" and are not likely to provide a true 0 ohms from one end to the other. The 2 cables at the bottom edge, are those the inverter feeds ? Not very symmetrical, battery at far end will see higher resistance. Center would have been better.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • benjaminbenjamin Solar Expert Posts: 34
    Re: Portable energy storage system

    The bus bars are 1/4" thick. The two wires at the bottom are coming from batteries. The wires to the inverters were not installed in that picture. They are as centered as I could get them and spread out in order to draw current as evenly as I think possible.

    This system will generally not see over 1000W or so, so hopefully the resistance won't be a factor. When we build our house we will be using this to power tools and the like so being able to handle large loads, if only briefly, was important.
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