solar school bus questions!

slurry bowl
slurry bowl Registered Users Posts: 34 ✭✭
in Caravan, Recreational Vehicle, and Marine Power Systems #1
Howdy.

I was asked to finish the electrical on a school bus with two 135 watt thin film panels.

The overall quality of the materials Ive been asked to install is very good and Id like to get some answers to burning questions, but first here is what Ive got:

2 135 watt panels with a Voc of around 45 volts.
Outback FLEX MAX80 charge controller
6 6v batteries, wired in 3 strings for a 12 V battery bank.
A variety of heavy duty inline fuses


Questions:

-The charge controller has no load lugs and Ive got to put the load wires on the same terminals as the wires used to charge the battery bank. Should I affix these with anti-corosion gell?

-Grounding the system is complicated because there is another battery used to start the bus. We had initially hoped to use an isolator to connect both batteries, but for now the systems are separate. My plan is to wire the battery bank and PV wires directly into the terminals of the charge controller and have the ground for the system connect to the chasis of the bus at one place. Others have told me that my neutral should be the frame of the bus, but that seems wrong. How often and where should I connect the system to the bonded metal of the bus. We have a welder and talked about installing chains. The system is fairly close to a propane tank used for cooking.

-What is a safe and cheap way to combine my two panels with a 15 amp breaker before landing in my charge controller?

-What is a safe and cheap 12 V load center that can have breakers or inline breakers already purchased and add an inverter?
This is critical because we want something to pull 12 V off of for lighting, frig, etc..safely.

THANKS For any input. pics to come!:D
· Share on Twitter

Comments

  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    #2
    Re: solar school bus questions!
    slurry bowl wrote: »
    2 135 watt panels with a Voc of around 45 volts.
    Outback FLEX MAX80 charge controller
    While that combo will work, you will be using a very expensive 80 amp controller to pass about 15 amps of current. Might make more sense if they plan to expand later.
    6 6v batteries, wired in 3 strings for a 12 V battery bank.
    I assume that this is going to be around 600 amp-hours at 12 volts. If so that's not much solar for that large a battery bank; it will be rare to get a full charge, and that will affect battery life. If you run the generator frequently to do a full charge it might work OK.
    -The charge controller has no load lugs and Ive got to put the load wires on the same terminals as the wires used to charge the battery bank. Should I affix these with anti-corosion gell?
    For protected-area copper on copper or copper on steel it's not critical, but it definitely can't hurt.
    Grounding the system is complicated because there is another battery used to start the bus. We had initially hoped to use an isolator to connect both batteries, but for now the systems are separate. My plan is to wire the battery bank and PV wires directly into the terminals of the charge controller and have the ground for the system connect to the chasis of the bus at one place. Others have told me that my neutral should be the frame of the bus, but that seems wrong.
    Normally you connect neutral and ground at one location in an RV system. However (important point) that link must be broken before you plug into shore power, since the shore power supply provides that. Most people use a relay to achieve this.
    What is a safe and cheap 12 V load center that can have breakers or inline breakers already purchased and add an inverter?
    I believe the Square-D QO line of breakers are DC-rated up to 48 volts, so a load center incorporating those breakers would probably be a good choice. For the inverter you probably want a direct connection to the battery, either fused or with a large separate breaker.
    · Share on Twitter
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: solar school bus questions!

    1st i think you could use more in pv for that size of a battery bank. be sure the lead lengths are equal and use thick enough wire for the loads.

    as to putting the load wires on the controller, don't do it. you will need to run wires from the batteries for the loads with the appropriate fuses/breakers for the wires. the controller is not the center of the system as the batteries actually are. the cc is for sending a regulated charge to the batteries and that's it. it is not to be used as a distribution box.

    you could use some sort of anti-corrosion stuff in connections as it certainly wouldn't hurt, but isn't required unless near large bodies of water or in a wet environment.

    i think the use of the chassis for ground is appropriate if the bus still goes mobile. btw, dc power does not have a neutral wire as that is for ac wiring. be careful if adding an inverter as many do not allow for the grounding.

    with that cc you can put the pvs in series or parallel, but if you wish to use a 15a breaker to switch it on and off with series would be the choice. btw, 2 pvs are not required to be fused or circuit breakered going to the cc. 3 or more parallel pvs or strings of pvs do need the fuse/cb.

    small dc load centers you can find in northern az wind and suns store as would be the case for other stores too, but the inverter will need a direct connection, with a fuse/cb nearest to the batteries for greater safety, to the battery due to it drawing heavy current. you do need to review your loads and for how long you intend to use them to determine at what point you are draining the batteries too far. 50% should be max as you don't want to drain the batteries further or risk shortening the battery life or ruining the batteries. you will find the pvs need to be expanded upon for handling the loads too, but get a better handle on what your loads will be over the course of a day and this will be either in amp hours or watt hours.
    · Share on Twitter
  • slurry bowl
    slurry bowl Registered Users Posts: 34 ✭✭
    #4
    Re: solar school bus questions!

    Ok thanks everyone. A few thoughts:

    -The Charge Controller is sized for more panels to be added down the road.

    -As far as DC wiring. My understanding is that the BLACK(or not HOT) or (NEUTRAL) needs to be wired as per diagrams( into terminals). I was told to not run this wire from the battery bank(only run the RED or HOT) and attach the BLACK to metal on the bus and then attach another wire to the metal on the bus near the battery, which I know has to be wrong. What I have learned from this forum is to wire it up as per diagrams and attach the BLACK wire to one place on the metal frame of the bus. Probably running off the grounding bar of my small breaker panel. And that this needs to be disconnected when another source of power is applied, does that mean when a generator is attached to the batteries.

    -The FLEXMAX80 seems overkill for the current system and Im thinking about recommending returning it and getting a Morningstar MPPT charge controller as I think they also have LOAD lugs at the charge controller and if I used hefty wire I could avoid having ANOTHER set of wires running to the batteries.

    -Having the charging wires, load wires, and inverter wires all on the same battery terminals seems tough because they are small terminals.

    -Why cant I run the inverter off the 12V load center with a heavy duty breaker and not run additional wires.

    I know Im asking alot, kinda brainstorming, thanks KINDLY for any input.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: solar school bus questions!
    slurry bowl wrote: »
    -The Charge Controller is sized for more panels to be added down the road.

    Look at how much power/panels they want to add... A high power/current 12 volt system can be problematic. A 1,200 Watt AC inverter on 12 volts looks like:

    1,200 Watts * 1/0.85 inverter eff * 1/10.5 battery cutoff * 1.25 NEC wiring/breaker derate = 168 amp minimum branch circuit rating
    -As far as DC wiring. My understanding is that the BLACK(or not HOT) or (NEUTRAL) needs to be wired as per diagrams( into terminals). I was told to not run this wire from the battery bank(only run the RED or HOT) and attach the BLACK to metal on the bus and then attach another wire to the metal on the bus near the battery, which I know has to be wrong. What I have learned from this forum is to wire it up as per diagrams and attach the BLACK wire to one place on the metal frame of the bus. Probably running off the grounding bar of my small breaker panel. And that this needs to be disconnected when another source of power is applied, does that mean when a generator is attached to the batteries.

    Be very careful with terms... "Neutral" is typically refering to the neutral/white wire of a 120/240 VAC split phase power system in North America.

    Technically, you can call a grounded 12 volt battery lead the "neutral" too... But it will probably confuse most people.

    The problem with the AC Neutral is that we only want the neutral to earth connection in one location (the main panel of the AC power panel in our home/business). And if you have a (typically) TSW AC inverter (true or pure sine wave), you can ground one of the AC outputs to the bus chassis and make it a "neutral". Good idea, but when you mix off grid power, generator power, and shore power--Who has the grounded neutral bond becomes a complex question.

    If you have a MSW inverter--You almost never want to ground reference the AC output--It will cause a short circuit with the MSW inverter if both the AC output and DC battery bank are ground referenced.

    A complex question that needs lots of clarification.
    -The FLEXMAX80 seems overkill for the current system and Im thinking about recommending returning it and getting a Morningstar MPPT charge controller as I think they also have LOAD lugs at the charge controller and if I used hefty wire I could avoid having ANOTHER set of wires running to the batteries.

    The "LOAD" terminals on a solar charge controller do not, in general, pass enough current for running any sort of medium or larger AC inverter--And are not needed/useful to have an LVD (low voltage disconnect) anyway (AC Inverter has one already). Do not use the LOAD terminals for anything, or at the most, small DC loads like LED lighting and small electronics.
    -Having the charging wires, load wires, and inverter wires all on the same battery terminals seems tough because they are small terminals.

    Then run everything to a set of common "Bus Bars" and make all your connections (and fuses/breakers in the + wiring as it leaves the bus bar) to all your loads and charging sources.
    -Why cant I run the inverter off the 12V load center with a heavy duty breaker and not run additional wires.

    You may--It depends on the rating/wiring of the DC load center... 12 VDC, you want only about 1/2 volt maximum voltage drop. Requires heavy gauge and short copper wire connections. Not all load centers are really designed for supplying 100's of amps of DC current as used in modern AC inverters on larger systems. Smaller inverters of a few hundred watts, a different animal.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: solar school bus questions!
    slurry bowl wrote: »
    Ok thanks everyone. A few thoughts:

    -The Charge Controller is sized for more panels to be added down the road.

    -As far as DC wiring. My understanding is that the BLACK(or not HOT) or (NEUTRAL) needs to be wired as per diagrams( into terminals). I was told to not run this wire from the battery bank(only run the RED or HOT) and attach the BLACK to metal on the bus and then attach another wire to the metal on the bus near the battery, which I know has to be wrong. What I have learned from this forum is to wire it up as per diagrams and attach the BLACK wire to one place on the metal frame of the bus. Probably running off the grounding bar of my small breaker panel. And that this needs to be disconnected when another source of power is applied, does that mean when a generator is attached to the batteries.

    Run separate negative and positive (black and red in wiring conventions) lines from battery to loads. Do not rely on the bus chassis for efficient negative connections. Automotive electrical applications do this because it is cheaper to use the chassis than to run wire. It is not better.
    -The FLEXMAX80 seems overkill for the current system and Im thinking about recommending returning it and getting a Morningstar MPPT charge controller as I think they also have LOAD lugs at the charge controller and if I used hefty wire I could avoid having ANOTHER set of wires running to the batteries.

    The FM80 can handle about 1250 Watts on a 12 Volt system. Is there room for that much? Figure out some realistic maximum panel space and see if a 30 Amp MidNite Kid wouldn't be a better choice here. Also re-evaluate that battery bank regarding actual power needs and ability to recharge it. Three parallel strings of (probably) GC2's: 660 Amp hours. That would ideally be recharged by 66 Amps of current coming from 1028 Watts of PV on the FM80.
    -Having the charging wires, load wires, and inverter wires all on the same battery terminals seems tough because they are small terminals.

    You will be using bus bars. Trust me: you have three parallel battery strings which need to go to some common connection point. From that point the controller and all loads can take power. And there will be fuses and/or breakers. Per battery string, per charge controller, and per load.
    -Why cant I run the inverter off the 12V load center with a heavy duty breaker and not run additional wires.

    See above notes on wiring. If this is mainly to power an inverter, go to a 24 Volt system. If you need 12 VDC for something, evaluate how much power is needed at that Voltage and consider supplying it with a DC to DC converter.
    I know Im asking alot, kinda brainstorming, thanks KINDLY for any input.

    Brainstorming is good. Especially BEFORE buying equipment.
    · Share on Twitter
  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    #7
    Re: solar school bus questions!
    slurry bowl wrote: »
    -Having the charging wires, load wires, and inverter wires all on the same battery terminals seems tough because they are small terminals.
    Definitely, and you do _not_ want to do that since those are all unprotected wires. I'd recommend you run only two lines to the battery:
    1) Inverter line (with appropriate fuse or breaker)
    2) Load panel line, with everything else connected to that.
    -Why cant I run the inverter off the 12V load center with a heavy duty breaker and not run additional wires.
    Depends on the inverter. Let's take the Prosine 1000, an inverter I have used in an RV application before. It will give you 1000 watts, which I used for regular AC loads and very occasional A/C and microwave usage. It surges to 1500 watts. At 11 volts that means 140 amps. That's going to be nearly impossible to do through a cheap load center.

    Now let's take the Morningstar Suresine 300, another (very popular) RV inverter. It will surge to 600 watts, which means it will handle lights, fans and small appliance loads (a small blender but not a toaster or microwave.) That's 55 amps. You might be able to do that with a 60 amp breaker - provided your runs are very short and your wire gauge is sufficient.
    · Share on Twitter
  • slurry bowl
    slurry bowl Registered Users Posts: 34 ✭✭
    #8
    Re: solar school bus questions!

    THANKS the info and advice so far.

    My current plan is to purchase two of these bus bars and run my battery positive and negative to them.
    http://www.bluesea.com/products/2314/Common_100A_Mini_BusBar_-_5_Gang_with_Cover

    Prior to the HOT landing on its bus bar, it will have a 100 amp circuit breaker.
    Then off of the bus bars I will have my LED lighting/Stereo/Small Fridge/and inverter, each with its own circuit breaker.

    I will ground the NEGATIVE to the bus chassis at one location, a pigtail off a terminal of the battery bank.

    I now understand that the inverter's rating of 1000/2000 watts is its standard wattage and temporary "burst" wattage. Im planning on running that off of my main bus bar because I dont really think it will be used that often and for much. It probably wont see many loads, maybe a laptop charger and phone charger.

    Im confused a bit about about BB's branch circuit rating of 168 amps for the inverter. That seems really high, I know with a 12V system, that can happen, but again what does that mean to me? 168 amps.

    We were told that dragging chains underneath the bus to maintain ground was a good idea. Is that really necessary?

    How would we connect a trickle charger or generator to this system?

    Lots of questions, thanks for all the input. The FlexMax80 has already been purchased so thats our charge controller.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: solar school bus questions!

    At 100 Amps that is a pretty small bus bar. 100 Amps @ 12 VDC nominal = 1200 Watts. At that point the bar will be cooking. I would deem this undersized for the application, especially if you are still planning on three parallel battery strings with their capacity of some 600+ Amp hours.

    Keep in mind that if battery Voltage is low and Wattage demand high the current will increase. 2000 Watt surge of the inverter at 11 Volts (or wherever shutdown occurs) would be 182 Amps and that is not including any other loads on at the same time.

    You do not need to establish an Earth ground in an RV application. Millions of vehicles roll down the road without dragging any chains behind them and have no problems at all. Some people toss out a grounding plate when they park, but it is probably quite ineffectual in most cases as the quality of ground contact is dubious. Best case scenario is to run your AC output isolated, with double pole breaker that will disconnect both lines in the event of a problem so nothing is hot in respect to ground. This is known as "floating neutral" and is often found on portable generators (where grounding is not practical).

    You can connect any AC powered battery charger to the positive and negative leads where convenient. Provide fuse/breaker on the output of course. It will not interfere with the solar.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #10
    Re: solar school bus questions!
    slurry bowl wrote: »
    I now understand that the inverter's rating of 1000/2000 watts is its standard wattage and temporary "burst" wattage. Im planning on running that off of my main bus bar because I dont really think it will be used that often and for much. It probably wont see many loads, maybe a laptop charger and phone charger.

    Size your battery bank and AC inverter to your loads... You don't need a 1,200 Watt AC inverter to run a 60 Watt laptop power brick.

    The 1,200 Watt inverter will work, and it some cases may cost less than a 300 Watt inverter (quality has its costs). And you can even wire up the 1,200 Watt inverter as if it is a 300 watt inverter (with smaller DC fuse/wiring based on 300 Watt maximum load).

    Gets back to Marc (Cariboocoot's) post this morning about "will this work or not" question. Yes it will work, it may waste a bit more power (a 1,200 watt inverter usually takes more power to "turn on"--Maybe 10-20+ watts, vs a small 300 Watt inverter's 6 watt Tare load).
    Im confused a bit about about BB's branch circuit rating of 168 amps for the inverter. That seems really high, I know with a 12V system, that can happen, but again what does that mean to me? 168 amps.

    I am guilty as charged. :p

    I am an engineer--You asked to run a 1,200 Watt inverter--I will assume you want to run it for 4+ hours at 1,200 Watt AC load (your space heater) until the battery is 20% state of charge. In reality, most of the time you are probably running an average of 400 Watts... And the battery bank will be >50% state of charge. And you will probably never pop the 100 amp fuse.

    However--If you do pop the 100 Amp fuse in the middle of nowhere--Will you have a spare or two? Circuit breakers are nice--No spare fuses needed, and CB's make a handy on/off switch for heavy loads.

    Where being conservative really helps--During charging. Solar arrays and AC Battery chargers can operate at 100% of their design loads for 2-4+ hours. And very few people have day to day experience of running their home loads like this (vacuum cleaner for 10 minutes at a time, maybe an electric space heater, etc.). Electric Water Heaters, Well Pumps, A/C systems are probably the only ones that come close to the steady state loads that Battery Charging can put on your AC grid/backup power/DC power system.

    For charging, it is almost always best to consider the worst case situation and design for it (battery near dead, maximum current, very bright sunny day, AC charger on your backup genset, properly sized/rated wiring and fuses/breakers, etc.).

    You will quickly find out that that generator+battery charger combination you tried out last summer (90% charged battery) all of a sudden starts lugging/AC outlet gets hot, etc. when you are trying to recharge your near dead battery bank and run some important loads after that large storm went through the neighborhood and took out the utility power. Running the genset at 80% of rated power maximum for 1/2 a day--And knowing it will actually support those loads--A wonderful feeling.
    We were told that dragging chains underneath the bus to maintain ground was a good idea. Is that really necessary?

    I would not use chains (noisy, wear quickly). There are rubber anti-static straps that you can use instead.

    But--Remember this is just for static electricity discharge--For example dry weather and you have been driving awhile and built up a static charge on vehicle body... Somebody comes up to open the door and gets a shock (or sometimes you go to put the gas pump nozzle into the tank and a spark lights off the fumes--Uncommon, but does happen).

    The grounding change/strap is not going to do anything for your Solar/Battery power system. Your system will operate exactly the same if that chain/strap is there or not.
    How would we connect a trickle charger or generator to this system?

    Can you tell us a bit more what you want to do? Trickle charging for long term storage--One thing (and should not be needed if you have solar power and no loads when parked/unused). Generator+AC charger to quickly bring a battery bank up after a day of no-sun/heavy loads, something else.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • slurry bowl
    slurry bowl Registered Users Posts: 34 ✭✭
    #11
    Re: solar school bus questions!

    Ok got it.

    I need a higher rated bus set-up, Im thinking a 150 amp in-line fuse to this:

    http://www.bluesea.com/products/2723/DualBus_Plus_150A_BusBar_-_5_16in-18_Stud_5_Gang

    Now for wire sizing the conductors coming from the battery....any advice?
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
    Re: solar school bus questions!
    slurry bowl wrote: »
    Ok got it.

    I need a higher rated bus set-up, Im thinking a 150 amp in-line fuse to this:

    http://www.bluesea.com/products/2723/DualBus_Plus_150A_BusBar_-_5_16in-18_Stud_5_Gang

    Now for wire sizing the conductors coming from the battery....any advice?

    Yes; nail down your expected current/loads. That is vital to sizing everything. On the DC side we're not talking about just power to the inverter but power to everything that will draw from the batteries. This will also help you pick the right size battery bank.

    Once you have the current worked out you also need to know the distances involved to keep Voltage drop under full load to a minimum.

    Basically you are looking at something like this:

    BATTERY--->FUSE/BREAKER--->BUS BAR
    BUS BAR--->FUSE/BREAKER--->LOAD1
    BUS BAR--->FUSE/BREAKER--->LOAD2
    BUS BAR--->FUSE/BREAKER--->LOAD3
    (Et cetera)
    BUS BAR<---FUSE/BREAKER<---CHARGE CONTROLLER
    BUS BAR<---FUSE/BREAKER<---AC CHARGER

    Each of those dotted lines and arrows represent a circuit that will be operating at a particular current. The wires in those circuits need to be sized to handle that current plus keep Voltage drop to a minimum. The fuse or breaker sized to handle the current; it will be a smaller value than the maximum the wire can handle because it is designed to go first in the event of a short.

    The battery to bus bar circuit will be the heaviest wire as it has to accommodate all loads on the bus bar simultaneously. For multiple battery strings it is a good idea to have a fuse or breaker per string. Many people use the Blue Sea battery terminal post fuses for this with good results. It keeps the protection close to the power source which prevents any energized wire being available if something goes wrong.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #13
    Re: solar school bus questions!

    To do things safely--Really need the details.

    What size/configuration of battery bank (series/parallel, AH rating, etc.).

    What is are your maximum continuous and surge loads (DC, AC through inverter, etc.).

    How long are the wire runs? 12 volt power takes a lot of copper to send a large amount of power any distances... 120 VAC is much easier.

    Conservation will be your friend here... There is a big difference between running a circular saw or microwave oven for 5-20 minutes a day vs running 200 Watts 12 hours per day (in sizing battery bank, wiring, charging circuits, etc.). Sizing your battery bank based on loads:
    • 1,500 Watt microwave * 15 minutes * 1/60 minutes per hour = 375 Watt*Hours = 0.4 kWH per day
    • 200 Watt desktop computer+network+printer+TV * 12 hours per day = 2,400 Watt*Hours = 2.6 kWH per day
    • 40 Watt laptop computer+Cell Phone * 12 hours per day = 480 WH = 0.5 kWH per day

    Sizing your Wiring based on wattage/current draw (note: NEC derating--Breakers/fuses will not pop at 80% of rated load, and will pop at 100% of rated load--That is why the 1/0.8 or x 1.25 NEC wiring derating):
    • 1,500 Watt * 1/0.85 inverter eff * 1/10.5 battery cutoff * 1.25 NEC derating = 210 Amp Branch Circuit Wiring
    • 200 Watts * 1/0.85 inverter eff * 1/10.5 battery cutoff * 1.25 NEC derating = 28 amp Branch Circuit Wiring
    • 200 Watts DC * 1/12 volt battery * 1.25 NEC derating = 20.8 amp Branch Circuit Wiring
    • 40 Watt laptop+Cell on inverter * 1/0.85 inverter eff * 1/10.5 battery cutoff * 1.25 NEC derating = 5.6 amp Branch Circuit Wiring

    The details matter.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • slurry bowl
    slurry bowl Registered Users Posts: 34 ✭✭
    #14
    Re: solar school bus questions!

    Thanks everyone.

    I think our loads are fairly simple and not too extravagant.

    170 watt refrigerator
    Laptop/Phone charger
    LED strip lighting
    small stereo

    I dont have the exact wattage but I plan to oversize the wire as per 310.15.b.16

    The client wants to save $ and has some thick car audio cable designed for brief high amp currents, he wants to run that from the battery bank to this load bus bar I purchased:

    http://www.bluesea.com/products/2723/DualBus_Plus_150A_BusBar_-_5_16in-18_Stud_5_Gang

    Then run the FLEXMAX80, Inverter, and other loads off the bus bar, therefore only having one connection to the battery bank. We will have everything with circuit breakers.

    I think the audio cable is a bad idea and think size 1 wire or 1/0 should be right. Any advice on that?

    ALSO....The 2 solar panels they want to use are long slender thin film 135 watt panels and the 6 batteries wired for 12V nominal will need to be fully charged by a generator on occasion. How would I connect a generator to this system? Perhaps into the charge controller? It needs to be relatively safe.

    THANKS
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #15
    Re: solar school bus questions!

    Audio cables many not be rated (UL LISTED) for any application. So you do not know how the insulation will react to oils, acid, heat, aging, ozone, hydrogen, etc.... It could harden and crack with age/exposure, a hot wire could melt through the insulation and then short, hot insulation could catch fire (easier than rated insulation), etc.

    If you want to do your own checking--Besides trying to get information on the insulation from the cable vendor--We would do "flame tests" on plastics used in telephone central office equipment to see if there was any "issues" with the wide array of plastics you find in computers systems/hard drives/circuit boards/power supplies/cabling/etc.

    One was called something like the "needle flame test"--basically a small propane or similar gas flame. Hold the material for XX seconds in the flame, then remove the flame. If plastics did not burst into scary flames/black smoke, it was OK (OK, it was more "technical" than that--But something like that).

    The other was to take a few ounces of alcohol (don't remember what type). Put it in a few cups, then put the lighted cups in a few different location in the computer rack. Let burn for X minutes, then try to put out the fires (if any) with a single extinguisher. Both look for how much burns, how easy to put out fire(s), and thickness of smoke.

    So--My suggestion--Get a couple of wire samples and try (in a safe environment) lighting off the insulation with a small propane torch flame and see how the different types of insulation respond.

    In the end, I would not not use "cheap/unmarked" audio cable--It is not usually designed for the job.

    You can get UL/NRTL Listed audio cable--But it is probably going to be as expensive as regular cable. There are different classes of insulation used in buildings--Up to "plenum" grade--Cable that has the least flammable/combustion products (you can run cables in air handling plenum--for example).

    http://site.ul.com/global/documents/offerings/perspectives/regulators/electrical/newsletters/W&CMG_April2007_Final.pdf

    It looks like Welding Cable is usually used for battery connections... From our host's website:

    http://www.solar-electric.com/lib/wind-sun/TryStarWeldingCable.pdf

    http://www.solar-electric.com/installation-parts-and-equipment/wiring-cables-and-connectors/hardware-wire.html
    The tray cable two-conductor wire (TC-8, TC-10, and TC-12) is best for most solar panel wiring where MC cables are not used, and for general outdoor wiring. It is sunlight resistant, approved for direct burial, and good for high temperatures. All of the 2 and 3 conductor tray cables listed may be used for AC or DC up to 600 volts, indoors or outdoors.


    Below is listed our complete selection of wire and cable for use in solar electric and backup power systems. All wire listed here is UL approved.


    Besides raw welding cable, we also have ready-made sets of battery interconnects and inverter cables.


    All welding cable is made in the USA by Trystar, and has an operating temperature of -50 to +150 degrees F. All welding cable is Type M (30 gauge strands). Welding cable has excellent abrasion, oil, acid, and solvent resistance. It is available by the foot.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #16
    Re: solar school bus questions!
    finish the electrical on a school bus with two 135 watt thin film panels

    Make sure the panels are easily replaceable in 5 years, thin film does not have a good lifetime . And you mentioned adding more panels down the line, you will have to make sure they are compatiable with the existing, or add them to a new controller. 2 controllers can feed the same battery bank.
    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 ,

    · Share on Twitter

Categories