Wire Size Between Batteries

democopy · July 2010

I have seached the forum for a definitive answer to the size of wire between batteries to no avail.

I have 4 AGM 100ah Batteries, have read anything from #6 to 2/0.

Parts stores seem to carry ONLY #6 or #4 but larger sizes are easily accessible.

What is recommended by the pros?

Also, Battery cable or Welding Cable? Which is best?

For 1000w Inverter 10' away from Batterys what size cable for that? Welding or Battery cable?

If this information is listed elsewhere, please link me to it.

Thanks

Cariboocoot · July 2010

Re: Wire Size Between Batteries

What are you running from the batteries? That's the issue: how much current draw you expect.
You could use 400 Amp/hrs of battery to run a small inverter for a long time, or a large inverter for a shorter time. The bigger inverter will draw more current to supply the end Watts. Battery cables have to be sized to accommodate the current draw, and they must be fused accordingly.

Slappy · July 2010

Re: Wire Size Between Batteries

also, what is the max currant draw for your inverter, or what size amp fuse do they recommend, better yet, what make and model is your inverter???

niel · July 2010

Re: Wire Size Between Batteries

there isn't a definitive answer, but i do have a few questions for you that may help us answer you better.
1> is this battery bank at 12v or is it at 48v as this makes a difference in voltage drop losses.
2> what kind of loads are you to normally carry as i'm sure you won't be at 1000w at all times?

electrically there is no difference if it's a welding type (lots of fine strands), regular stranded, or solid as identical gauge #s on wires will have the same current capacity. if making the connections yourself it may become difficult to put connectors on stranded or welding type cables.

BB. · July 2010

Re: Wire Size Between Batteries

Wire gauge for a battery bank really depends a lot on your expected loads (and charging current).

For example, a good maximum current to plan for from a battery is around C/2.5 or so (AGM's can go higher than flooded cell--but got to start somewhere). Another thing is voltage drop... With heavy loads and a partially discharged battery bank you could see 11.5 volts from your 12 volt bank. And most loads will consider 10.5 volts as a "dead battery". So, lets assume that you have 1 volt drop and only want to "waste" 0.1 volts at C/2.5 discharge rate for your 100 Amp*Hour battery. Also, lets assume 1' foot wire run on each terminal to the bus bar.

100 AH / 2.5 = 40 amps

Using a typical voltage drop calculator (this one uses "1 way" wire length--so in this case that is 1 foot). Playing around I get:

1 foot one way run of 10 AWG wire running 40 amps = 0.1 volt drop

Not bad--but that is only 40 amp * 12 volts = 480 watts of power... Say your load is a pump motor and you want to support a 10x surge current without your inverter cutting out... Now we are talking about 400 amp surge:

1 foot one way length run of 1/0 (one ought) 400 amp would be 0.09 volt drop

Next, Lead Acid batteries can output 1,000's of amps (even smaller batteries like these) into a dead short. So--you should fuse / breaker protect your wiring against shorts.

An "0" cable will sustain around 150 - 245 amps of current--so you should fuse for that range too. Here is a neat battery terminal mounted fuse+holder.

Question about Welding Cable vs Regular NEC type cables...

The down side to welding cables is that they have very fine wire (to be flexible without work hardening the copper)--Great for places where flexing is an issue. Not usually needed for a battery bank (typically easier to terminate stranded cable that does not have fine wire).

You also have to look at the temperature and acid/solvent rating of the insulation... Typically NEC rated cables are referred back to the National Electric Code. Welding cable may not be.

That being said, many people use welding cable and are very happy.

Regarding the cable run to your inverter... Typically, again I would suggest that you place the inverter as close as practicable to the battery bank/bus connection point.

Lets say you have a 1,200 watt 12 volt inverter (note, 24 and 48 volt battery systems are easier to work with because the have less current and allow more voltage drop--12 volt is actually quite difficult to get a lot of power out of a bank because of the voltage drop issues). A 1.2 kW inverter usually supports a 2.4 kW surge. Lets say you allow 0.9 volt drop in your inverter wiring... Same as above:

2,400 watt * 1/0.85 inverter eff * 1/10.5 volt min operate = 269 amps
Wire gauge required for 10' one way run 0.9 volt drop = 1 awg cable (0./8 volt drop)

Anyway--I will stop here--I am probably confusing one of us with this long post. :roll:

Questions?

-Bill

democopy · July 2010

Re: Wire Size Between Batteries

Cariboocoot wrote: »

What are you running from the batteries? That's the issue: how much current draw you expect.
You could use 400 Amp/hrs of battery to run a small inverter for a long time, or a large inverter for a shorter time. The bigger inverter will draw more current to supply the end Watts. Battery cables have to be sized to accommodate the current draw, and they must be fused accordingly.

Some ham radio gear, some CFL lights, LED lights, etc. Not alot! Inverter will run laptop, perhaps printer occasionally.

democopy · July 2010

Re: Wire Size Between Batteries

Slappy wrote: »

also, what is the max currant draw for your inverter, or what size amp fuse do they recommend, better yet, what make and model is your inverter???

Am considering this:
http://www.duracellpower.com/power-inverters/recreation-inverters/inverter-1000.aspx

or perhaps this:
http://store.solar-electric.com/used-exxp12vol11w.html

Suggestions?

democopy · July 2010

Re: Wire Size Between Batteries

niel wrote: »

there isn't a definitive answer, but i do have a few questions for you that may help us answer you better.
1> is this battery bank at 12v or is it at 48v as this makes a difference in voltage drop losses.
2> what kind of loads are you to normally carry as i'm sure you won't be at 1000w at all times?

electrically there is no difference if it's a welding type (lots of fine strands), regular stranded, or solid as identical gauge #s on wires will have the same current capacity. if making the connections yourself it may become difficult to put connectors on stranded or welding type cables.

Battery Bank is 12v.

Loads on inverter laptop, drill once in a while, a small microwave if it works?

RCinFLA · July 2010

Re: Wire Size Between Batteries

For a 12v 1000 watt inverter with a distance of 10 feet, I would go with #2. It is about the largest gauge that will fit typical 1000 watt inverter terminal holes.

That will give you 0.16 vdc drop at full load on inverter (about 100 amps).

Welding cable is nice and flexible. Try to get Excelene which is top quality insulation.

If your load is less, then you can go with smaller gauge but why use a 1000 watt inverter then that has higher no load current drain.

for 10' distance between battery and inverter,

500 watts -> #4 gauge give 0.125 vdc loss.
200 watts -> #8 gauge gives 0.130 vdc loss.
100 watts -> #10 gauge gives 0.10 vdc loss.

democopy · July 2010

Re: Wire Size Between Batteries

BB. wrote: »

Wire gauge for a battery bank really depends a lot on your expected loads (and charging current).

For example, a good maximum current to plan for from a battery is around C/2.5 or so (AGM's can go higher than flooded cell--but got to start somewhere). Another thing is voltage drop... With heavy loads and a partially discharged battery bank you could see 11.5 volts from your 12 volt bank. And most loads will consider 10.5 volts as a "dead battery". So, lets assume that you have 1 volt drop and only want to "waste" 0.1 volts at C/2.5 discharge rate for your 100 Amp*Hour battery. Also, lets assume 1' foot wire run on each terminal to the bus bar.
100 AH / 2.5 = 40 amps

Using a typical voltage drop calculator (this one uses "1 way" wire length--so in this case that is 1 foot). Playing around I get:
1 foot one way run of 10 AWG wire running 40 amps = 0.1 volt drop

Not bad--but that is only 40 amp * 12 volts = 480 watts of power... Say your load is a pump motor and you want to support a 10x surge current without your inverter cutting out... Now we are talking about 400 amp surge:
1 foot one way length run of 1/0 (one ought) 400 amp would be 0.09 volt drop

Next, Lead Acid batteries can output 1,000's of amps (even smaller batteries like these) into a dead short. So--you should fuse / breaker protect your wiring against shorts.

An "0" cable will sustain around 150 - 245 amps of current--so you should fuse for that range too. Here is a neat battery terminal mounted fuse+holder.

Question about Welding Cable vs Regular NEC type cables...

The down side to welding cables is that they have very fine wire (to be flexible without work hardening the copper)--Great for places where flexing is an issue. Not usually needed for a battery bank (typically easier to terminate stranded cable that does not have fine wire).

You also have to look at the temperature and acid/solvent rating of the insulation... Typically NEC rated cables are referred back to the National Electric Code. Welding cable may not be.

That being said, many people use welding cable and are very happy.

Regarding the cable run to your inverter... Typically, again I would suggest that you place the inverter as close as practicable to the battery bank/bus connection point.

Lets say you have a 1,200 watt 12 volt inverter (note, 24 and 48 volt battery systems are easier to work with because the have less current and allow more voltage drop--12 volt is actually quite difficult to get a lot of power out of a bank because of the voltage drop issues). A 1.2 kW inverter usually supports a 2.4 kW surge. Lets say you allow 0.9 volt drop in your inverter wiring... Same as above:
2,400 watt * 1/0.85 inverter eff * 1/10.5 volt min operate = 269 amps

Wire gauge required for 10' one way run 0.9 volt drop = 1 awg cable (0./8 volt drop)

Anyway--I will stop here--I am probably confusing one of us with this long post. :roll:

Questions?

-Bill

Am considering THREE 100w panels or perhaps FOUR. Probably 24v hookup, MPPT controller.

Three to four panels and four batteries a nice mix for light to medium duty use?

Running home office.

So 1/0 Cable between batteries for 10-12' run from batteries to 1000w inverter?

Size cable between batteries 1/0?

Battery cable wire is better than welding cable if not U/L approved?

democopy · July 2010

Re: Wire Size Between Batteries

RCinFLA wrote: »

For a 12v 1000 watt inverter with a distance of 10 feet, I would go with #2. It is about the largest gauge that will fit typical 1000 watt inverter terminal holes.

That will give you 0.16 vdc drop at full load on inverter (about 100 amps).

Welding cable is nice and flexible. Try to get Excelene which is top quality insulation.

Could not find larger sizes in welding cable locally so was looking at this:
https://weldingsupply.securesites.com/cgi-bin/einstein.pl?PNUM::1:UNDEF:OR:304-1170

When doing the ring connectors on welding or battery cable:

Solder & Crimp?

Crimp Only?

Solder Only?

RCinFLA · July 2010

Re: Wire Size Between Batteries

So what's the probability that a 1000 watt 12v inverter, probably China sourced, is UL approved?

Welding cable is not UL approved.

Soldering depends on your ability. It is a NEC no-no but I prefer it over crimped. Crimping tool for large lugs are expensive.

Excelene insulation is high temp resistant, much better for soldering. Polyvinyl turns to bubble gum with heat. I tear a piece of an old bath towel into 1 " wide x about 8" strips and soak with water. I use propane torch.

Wrap wet towel strip around insulation up to strip back point. Coat with non-acid flux, I prefer the white water soluble flux. Insert stripped back wire about half way into solder lug and tin wire and inside of lug with solder. When full of solder push down into solder lug with final heating. Takes a little practice to get the amount of solder right.

If you pull and compress insulation toward center of wire you can end up with a tight fit of insulation to solder lug after insulation is expanded back when cooled off.

Keep the cables taped together for the 10-12' length. This decreases inductance which cuts down on surge voltage spikes from wire inductance.

http://store.weldingdepot.com/cgi/weldingdepot/scan/fi=products/st=db/sp=results/co=1/sf=category/se=Welding%20%26%20Power%20Cable/op=eq/nu=0/bs=1/ml=25/tf=description/to=x/se=1/sf=inactive/op=ne/sf=tax_category/se=1/op=eq/va=banner_text=/va=banner_image=.htm

BB. · July 2010

Re: Wire Size Between Batteries

I was giving an example of pulling 400 amps (or whatever) from one battery... If you have 4 batteries, you could derate by 1/2 (in theory, even 1/4--but current sharing between batteries is not always equal).

Plus, depending on how you wire your batteries (see Smartgauge website for proper wiring suggestions) -- you may have longer runs that I suggested.

Also, you may have less than the 2,400 watt surge current too... Pick the current value/voltage drop you want to support, look at practical wire lengths, the re-run the calculations (using the voltage drop calculator is just a cut and try process. And using that 3 AWG change is about a 2x increase in wire area/current capability to estimate how far you need to jump for the next wire size to try).

UL for insulation is nice--but you are not going to have a building inspector looking at your installation (I guess). Many times in solar, you are using much heavier wire to reduce voltage drop-so there is little chance of the wire overheating in normal operation. Fuses/Breakers protect wiring from dead short.

Ideally, a good crimp (right sized fitting, correct crimp tool, proper crimp) is the best way to do it.

Note, welding cable can be difficult to find crimp connectors to fit (00 high flex welding cable copper is "thicker" than 00 stranded wire). There are some "inexpensive" Chinese hydraulic crimp tools out there that people have used and like.

You can also use the manual crimp tool (sledge, tool, anvil) to crimp heavier cables.

Solder--Is considered a bad thing. Solder is first to melt and the wire can pull from the fitting. Then drop into something else and short circuit... On the other hand, I have soldered more than my fair share of battery cables.

A proper mechanical crimp will be "gas tight" and not let solder wick into the joint anyway. Solder cause a "fulcrum point" in stranded wiring and will focus bending at there the solder ends--causing earlier life failure from flexing vs a proper crimp only connection (obviously if there is little flexing, the cable is not going to break with three bending events).

Here is one thread discussing battery cables and connections.

-Bill

niel · July 2010

Re: Wire Size Between Batteries

i always advocated using larger wires to interconnect batteries with each other so maybe 2/0 if you can and minimally the same as the largest wire gauge you are using. for battery interconnections it is vital to keep everything equal and low resistance there.
you do have a capability of some large loads with your said list as some run linears and some don't. radios themselves vary greatly too so be sure you aren't going to overly tax you battery bank. most ham stuff is primary on 12vdc so odds are you won't need 1000w for an inverter. also note the exeltech is a quality sine wave inverter and the other is a lesser quality modsine inverter. we recommend the sine wave type if you need to run anything that has an electric motor in it or has more critical requirements warranting better inverter equipment. some wall adapters have also been known to smoke on modsine as well as some wireless tools. most will likely operate though, but you don't know which might actually pop with modsine. at the very least modsine inverters have a high amount of harmonics and could cause more power to be consumed by an appliance than sine wave types would.
be sure that if any inverter you buy is going to be returnable if the inverter gives off emi or rfi to your ham stuff.

Slappy · July 2010

Re: Wire Size Between Batteries

To touch on niels comment about the mod sine wave (msw) inverter, all motors that i have tried with a msw gives of a funny humm, some motors are louder than others, tried it on fans (ceiling/table top/floor/ type fans), but after awhile that sound gets irritating. and i have read some where that a microwave takes a little longer to heat food/liquids.

If all possible go for a pure sine wave type inverter.

sawmill · July 2010

Re: Wire Size Between Batteries

You might want to consider using buss bars for your interconnects. With a buss bar you eliminate one connection at each battery post. Using crimpted (and or) soldered ends for battery lugs is one connection that you can NEVER inspect or clean after installation.

Another advantage with this type of interconnects, it is a simple matter to connect your charging sources and inverter cables to your postive and negative termination points just by drilling the necessary bolt holes.

Anytime you can decrease the number of DC connection points is a good thing.

democopy · July 2010

Re: Wire Size Between Batteries

RCinFLA wrote: »

So what's the probability that a 1000 watt 12v inverter, probably China sourced, is UL approved?

Welding cable is not UL approved.

Soldering depends on your ability. It is a NEC no-no but I prefer it over crimped. Crimping tool for large lugs are expensive.

Excelene insulation is high temp resistant, much better for soldering. Polyvinyl turns to bubble gum with heat. I tear a piece of an old bath towel into 1 " wide x about 8" strips and soak with water. I use propane torch.

Wrap wet towel strip around insulation up to strip back point. Coat with non-acid flux, I prefer the white water soluble flux. Insert stripped back wire about half way into solder lug and tin wire and inside of lug with solder. When full of solder push down into solder lug with final heating. Takes a little practice to get the amount of solder right.

If you pull and compress insulation toward center of wire you can end up with a tight fit of insulation to solder lug after insulation is expanded back when cooled off.

Video on Soldering Battering Terminals

Poor mans way rather than solder plugs is fill the ring connector halfway full of solder, then add the wire.

Do you need shrink tube whether soldered or crimped. I see most factory made cables do not have it?

BB. · July 2010

Re: Wire Size Between Batteries

Shrink tubing is not required... But if it can help keep acid off the parts--not a bad idea.

For smaller cables, high end crimp connectors have two parts--one crimps on the copper, the other crimps on the insulation jacket for stronger / less bending stresses at crimp joint.

I like to use various coatings designed to protect battery posts/connectors from corrosion.

Silicon dielectric grease is an option--but for me, more of a last choice rather than a first one. Silicon tends to migrate and if you have any switch contacts in the area--the fumes can actually form "glass" in the contacts as they arc during switching.

Dielectric Grease Discussion
Some more talk about making good electrical connections (read through thread)
More talk about crimp/solder/no-ox greases

-Bill

democopy · July 2010

Re: Wire Size Between Batteries

niel wrote: »

also note the exeltech is a quality sine wave inverter and the other is a lesser quality modsine inverter. we recommend the sine wave type if you need to run anything that has an electric motor in it or has more critical requirements warranting better inverter equipment. some wall adapters have also been known to smoke on modsine as well as some wireless tools. most will likely operate though, but you don't know which might actually pop with modsine. at the very least modsine inverters have a high amount of harmonics and could cause more power to be consumed by an appliance than sine wave types would.
be sure that if any inverter you buy is going to be returnable if the inverter gives off emi or rfi to your ham stuff.

Any better value than the exeltech?

Recommendatations of inverter that will NOT cause emi or rfi problems?

Slappy wrote: »

If all possible go for a pure sine wave type inverter.

BB. wrote: »

Here is one thread discussing battery cables and connections.

-Bill

Excellent information!

How about enlightening me on series wiring of Three 100w panels?

Panel One to Panel Two + to -
Panel Two to Panel Three + to -
Same reverse other side
Then Panel One or Three + or - to controller
Opposite One of Three + or - to the controller?

If my calculations are correct?

300w/12 = 25amps
300w/36 = 8.33 amps

So the Morningstar SunSaver 15 Amp MPPT Solar Charge Controller should work fine on 36v to the 12v AGM Batteries?

Could a FOURTH panel be added in any way in the future to work with this controller and not exceed its limits? A fourth panel for my location is very unlikely.

BB. · July 2010

Re: Wire Size Between Batteries

For inverters, look to see if they are FCC class A or class B... Not a lot of vendors out there actually bother to get FCC (or UL/NRTL) for their products believing it is "not required".

Xantrex and MorningStar both seem to have may product that is FCC and UL/NRTL rated.

Your calculations are OK for the output of an MPPT Type solar charge controller output... Realistically, 95%+ of the time, you could derate the solar panels and charge controller to ~0.77 of the panel STC rating and be very happy. Unless you are in snow (cold weather and reflections from snow pack), you will seldom see >~86% of rated output from your solar RE panels + charger.

MPPT Controllers are self regulating for current--within practial limits, you can connect any large amount of solar panels and the controller will limit its output current to its rated maximum. In fact, a few people have connected a MorningStar MPPT controller to a 24/48 volt battery bank to efficiently down convert and charge a 12 volt battery (with appropriate fusing).

PWM controllers cannot take series panels (36 volts into a 12 volt battery bank) efficiently--and many will over voltage/damage.

You need to make two calculations for your panels Vmp-array Hot and Voc-array cold. The Vmp Hot to make sure you panels still charge the battery bank on a hot day. Voc cold to make sure that the solar charge controller's Vin-never-exceed is not exceeded.

From another post--the Math calculations (many solar charge controller/GT inverter vendors have on-line tools to do the calculations for you):

BB. wrote: »

Actually, the Voltage Change is the actual cell temperature and Ambient Temperature is only part of the equation... The other part (besides solar radiation) is wind and radiative cooling (mounting panels against roof vs mounted out in free air on a pole/rack). Ideally, the recommendation is to not mount flat and to have at least 5" behind the panels to allow for better cooling.

For the panel you asked about, it should be around -157 mV/C and worst case assume 35C (63F) cell temperature rise over ambient (STC = 77F). (they do not list the temperature coefficient--just guessing on my part).

So, the Vmp at 100F and 63F rise; and Voc cold at 14F:
-0.157 V/C * 1/1.8 C per F = -0.0872 V/F

34.9 Vmp + (-0.0.0872 V/F * (100F+63F-77F)) = 27.4 volts Vmp Hot

26.8 Volts * 2 panels in series = 54.8 Vmp Hot for 2 series panels

43.2 Voc + (-0.0.0872 V/F * (14F -77F)) = 48.7 volts Voc Cold

Even without any voltage/controller drop--that is barely float voltage for a 48 volt lead acid battery bank on a hot day.

Three panels in series will work for Vmp-array Hot:
3*27.4 Vmp hot = 82.2 volts Vmp Hot

3*48.7 Voc cold = 146 volts Voc Cold

Notice that Voc Cold with three panels is very near the maximum rated voltage for most high end MPPT charge controllers (typically 150 Volts never exceed).

This is the problem with panels with Voc in the ~40-70 volt range on 48 volt battery banks... They cannot be used in many climates on 48 volt battery banks with MPPT (or PWM) solar charge controllers. They would work fine with 12 volt or 24 volt battery banks.

I used 100F and 14F for the Hot and Cold panels plus 63F rise (assuming poor air flow). You can change the equations to your particular needs (put in a spread sheet--much easier ).

-Bill

mike95490 · July 2010

Re: Wire Size Between Batteries

sawmill wrote: »

You might want to consider using buss bars for your interconnects. ...<snip>...

A buss bar is NOT an interconnect. Your interconnect cable goes from the battery terminal to the buss bar. It's real hard to bend a heavy copper bar to fit to a battery post.

democopy · July 2010

Re: Wire Size Between Batteries

To Summerize:
Battery Interconnect Wire:
#4 & #2 No
#1 Will Work
1/0 Wire OK
2/0 Wire Better

Solder Ring Connectors: No

Crimp Ring Connectors: Yes

Wire Interconnect or Buss Bar works either way? One better than the other?
Home Made Buss Bar
Home Made Buss Bar In Use

Shrink Wrapping Cable Ends is not necessary if crimped correctly, using a good connector and crimp.

Wire Size from batteries to controller:
For 10' distance between battery and inverter,
1000 watts -> #2 gauge give 0.125 vdc loss.
500 watts -> #4 gauge give 0.125 vdc loss.
200 watts -> #8 gauge gives 0.130 vdc loss.
100 watts -> #10 gauge gives 0.10 vdc loss.

Questions:

Is the 3/100w 12v Panels and 4/100ah 12v AGM Batteries a good balance for my use? Three panels is max where I want to install them. So could go less on batteries or more for my application?

Inverter wire to appliance(s) 12ga good for up to 50'?

Fuses from battery to Inverter 125amp in-line Positive side only?

Can a 900-1000w Microwave be used less than 5 minutes without problems?

Can these type of ANL fuses be used in-line on the batteries, or is there something better. I know there are many that are alot more money.

mike95490 · July 2010

Re: Wire Size Between Batteries

I like this fuse block/terminal from Blue Sea
http://bluesea.com/category/5/21/productline/overview/378

You can use that many (400ah) AGM batteries with the 3 (300W) panels since you don't have to have EQ current, but you are on the low side, and must allow enough sun to recharge them. It will be easy to pull them down low and not get them recharged with your small array, fewer batteries won't help. A small genset would help if you get behind.

BB. · July 2010

Re: Wire Size Between Batteries

democopy wrote: »

To Summerize:
Battery Interconnect Wire:
#4 & #2 No
#1 Will Work
1/0 Wire OK
2/0 Wire Better

Really depends on current, wire length, and how much voltage drop you can accept.

Wire Interconnect or Buss Bar works either way? One better than the other?
Home Made Buss Bar
Home Made Buss Bar In Use

Probably personal choice if everything done nicely.

Wire Size from batteries to controller:
For 10' distance between battery and inverter,
1000 watts -> #2 gauge give 0.125 vdc loss.
500 watts -> #4 gauge give 0.125 vdc loss.
200 watts -> #8 gauge gives 0.130 vdc loss.
100 watts -> #10 gauge gives 0.10 vdc loss.

Assuming 12 volt DC input?

Questions:

Is the 3/100w 12v Panels and 4/100ah 12v AGM Batteries a good balance for my use? Three panels is max where I want to install them. So could go less on batteries or more for my application?

Rough range of recommended charging power from solar panels:

4 * 100 AH * 14.4 volts charging * 5% minimum charge * 1/0.77 derating = 374 watts
4 * 100 AH * 14.4 volts charging * 5% minimum charge * 1/0.77 derating = 972 watts

Inverter wire to appliance(s) 12ga good for up to 50'?

Should be fine--Use typical AC home wiring rules (typically 3% drop maximum).

Fuses from battery to Inverter 125amp in-line Positive side only?

To calculate minimum wire size for an inverter:

Load Watts * 1/low bat voltage * 1/inverter eff * 1.25 NEC wire/breaker derating = minimum wire/fuse rating
1,000 watts * 1/10.5 volts * 1/0.85 eff * 1.25 = 140 Amps Minimum

Round up to next standard wire/fuse size.

Can a 900-1000w Microwave be used less than 5 minutes without problems?

Depends on the inverter (5-10 minutes is near continuous rating for an inverter). Remember that Microwave Ovens also have efficiency issues too (more so with MSW type inverters). Use a Kill-a-Watt meter if you can.

Can these type of ANL fuses be used in-line on the batteries, or is there something better. I know there are many that are alot more money.

ANL Fuse ratings:

ANL Fuse Blocks

750 Amperes max, for systems up to 32 Volts, Large heat dissipating tin-plated copper mounting blocks, insulating cover

Maximum DC voltage and Maximum DC current (interrupt capability) are the two things to look when choosing fuses.

-Bill

sawmill · July 2010

Re: Wire Size Between Batteries

mike90045 wrote: »

A buss bar is NOT an interconnect. Your interconnect cable goes from the battery terminal to the buss bar. It's real hard to bend a heavy copper bar to fit to a battery post.

You are correct about the terminolgy, my mistake.

But the fact remains that a solid copper bar (sized for ampacity) is superior to a crimped soldered connection. If there is evidence to the contrary, please post the information. Once that connection is crimped and soldered it can never be inspected or cleaned. You have no way of knowing the integrity of the connection except by a destrutive autopsy or sophisticated test equipment.

There must be a reason the large standby banks use solid copper interconnects to series their batteries. The NEC has information that relates to solder for electrical use. I believe that NASA has also addressed these type of connections?

I didn't understand your comment about "bending to fit a post". On my bank it is a straight line positive to negative to series the interconnects. In the event different battery lugs could require 90 degree bends, copper is a mallable soft metal that is easily bent by the use of vise.

mike95490 · July 2010

Re: Wire Size Between Batteries

sawmill wrote: »

I didn't understand your comment about "bending to fit a post". On my bank it is a straight line positive to negative to series the interconnects. In the event different battery lugs could require 90 degree bends, copper is a mallable soft metal that is easily bent by the use of vise.

The buss bars I use are 1/4" thick and 1.5" wide. I can do chin-ups on it. They will not bend to bolt to a battery, and thermal expansion will eventually tear the terminal post off the battery.

I'd had no way to know that you used the wrong word.

Mike "it is all about the words you use" B.

sawmill · July 2010

Re: Wire Size Between Batteries

mike90045 wrote: »

The buss bars I use are 1/4" thick and 1.5" wide. I can do chin-ups on it. They will not bend to bolt to a battery, and thermal expansion will eventually tear the terminal post off the battery.

I'd had no way to know that you used the wrong word.

Mike "it is all about the words you use" B.

Kinda makes you wonder how the large telecom battery banks deal with this problem of battery post tear off?

BB. · July 2010

Re: Wire Size Between Batteries

Typically, Telecom buildings have thick concrete walls (at least around here) lots of A/C and Heating to keep the insides at a stable temperatures and the batteries are not usually cycled with high currents (they don't thermal cycle much either).

So--Bus Bars / thermal flexing is probably not normally a big issue for them... And if the batteries ever get heavily cycled (power failure, genset failure), they may end up replacing the bank anyway.

In a smaller battery bank that experiences significant thermal cycling (near freezing to hot summer)--not having flexible bus bars may be a bit more of an issue... But given that many batteries that experience very heavy usage (i.e., forklift/traction batteries) use some version of internal bus bars for cell to cell connections--I am not sure it is a huge problem.

-Bill

democopy · July 2010

Re: Wire Size Between Batteries

Thanks so much for all the help and information, trying to digest it all and formulate a plan of attack.

Have read that a shunt should be installed, close to the batteries and off the negative post, a reference was made to this: Deltec 500 amp 50 mv Current Shunt. Do I need one of these on a small system and what does it do and is this the right place to install it?

Fusing from the batteries to the load and before a disconnect switch, can one of these be used and what amp? Littelfuse 298900 Automotive Single Terminal Fuse Holder

Same fuse and what size to the inverter?

icarus · July 2010

Re: Wire Size Between Batteries

You only need a shunt if you are going to wire a current meter in your system. The purpose of a shunt is to essentially serve as a "pick up" point for a ammeter, so that the entire current doesn't have to run through the meter.

Be advised, that many meters come with a shunt, (Tri-metric for example).

As for the fuse, the one you link will work fine, but I might suggest the battery terminal one offered by Blue Sea. http://bluesea.com/category/5/21/productline/overview/378

No muss, no fuss,

Tony

democopy · July 2010

Re: Wire Size Between Batteries

icarus wrote: »

As for the fuse, the one you link will work fine, but I might suggest the battery terminal one offered by Blue Sea. http://bluesea.com/category/5/21/productline/overview/378

No muss, no fuss,

Tony

Hi Tony,

Thanks for your quick response.

If I use the MPPT Morningstar Controller and add a remote display box, then do I need the shunt?

Is the shunt wired right after the batteries on the negative side?

The Blue Sea Fuse you linked below, would go on EACH battery? So FOUR of them if I have FOUR batteries?

The fuse I linked to would handle all the batteries after the lead comes off the battery, correct?

What size fuses on the batteries?

What size fuses going to the inverter?

What size fuse going from the panels to the controller?

Thanks

Wire Size Between Batteries

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