Battery interconnections

Re: Battery interconnections

I am not a big fan of bus bars, but see this for some info on battery hookups

http://www.sunxtender.com/pdfs/Sun_Xtender_Battery_Technical_Manual.pdf

Re: Battery interconnections

I vote for figure 5-9 with one modification, add a fuse at each positive to bus connection.

Re: Battery interconnections

careful john as you don't know the ohms per 1000ft of the copper pipe you are using. you can't even go by its weight as different pipes can have different impurities and/or alloys in them. you just don't know if it is actually sufficient for all bus applications, but it can be physically configured with copper pipe with some degree of success.

Re: Battery interconnections

as far as my own wiring goes, yes i do look up the resistance as a factor as this involves voltage drop. wires have known resistances with each gauge number or in the case of many outside of the u s, the mm. bus bars are no different as they need to be able to meet certain resistance criteria or current capability. do you think it's ok for me to use a thin wire in my battery connections just because the resistance shows it to be low being only 1 ft long? if anything it should be even lower in resistance to insure equality between batteries and that higher currents will not be impeded and it is a part of a bigger picture involving voltage drop. using pipe introduces and unknown factor into the system.
pipes not only, as i stated before, come with different alloys and impurities, but they come in different thicknesses too so it is important to get a handle on what it is you are using to at least have some idea on it.

Re: Battery interconnections

john p wrote: »

You are correct Niel I have no idea of the ohms per 1000 ft of copper tubing,And to be honest I think even knowing it would be useless information.
Let me ask this when you have ever used copper cable for any battery connection did you ever find out its resistance per 1000ft? Have you ever personally measured a cable or had someone use an extremely accurate meter to read resistance of a cable before you used it?? or do you just use the standard published figures for the average cable and hope the one you are going to use is going to have a resistance something like that of the published one.?
I think its going to be difficult to get an accurate reading of a pipes resistance when only using about less than 1ft.
But out of curiosity next week I will try to con the place where I work into buying a few random lengths of pipe 3/4 dia and about 10ft lengths.We have an very accurate device to measure resistance . I will post the results.
I really believe 2 lugs on a 9" length of #2 copper cable would have a greater resistance than ANY 9" length of 3/4 copper pipe

but it can be physically configured with copper pipe with some degree of successWell I must have been just always lucky as its always been 100% successful for me.

Here are some specs for "electrical" copper tubing. Multiply resistance about X4 for unknown home-depot tubing type L.

http://www.stormcopper.com/copper-bus-tubing-specs.htm
http://www.engineeringtoolbox.com/astm-copper-tubes-d_779.html

Re: Battery interconnections

john p wrote: »

BB thats is why I derated it by a very generous factor of 4 as was requested to do for unknown copper water pipe. But even after that it can carry more amps than any home user is ever going to use.
Some how everyone has missed the point of my first post about battery interconnects. It was not aimed at the person charged with designing a 10GW solar plant ,It was ment for the home user that is likely to be doing something like this.. connecting 4x6v high amp batts in series.connecting 3or 4 12v batts in parallel or a combination of the above and using a inverter of up to 2kw.For that person to use 3/4 copper pipe is perfect for the interconnects and for the negative wire returns, it makes a great simple buss bar,
A major problem for home handy person is making really good crimp joints on lugs at #4 wire size and above.I have seen some people try to hammer them flat .but because of springiness in the lug it makes for lousy joint .Although flat jawed vice grips can do a ok job on #4 cables.Where I work we use a 10 ton press with deep serated jaws then do the finger test ,, we connect the cable to a 100a load across a 12v batt for 5 mins and then touch the lug if its still cool its good.its then heated as little as possible and no lead solder is fed into the back of the lug until its full. then glue heat shrink is fitted.

A simple tool like this and a small sludge hammer makes nice wire crimps. One hit to set, two to make sure.

http://crimpsupply.com/tools/crimping-tools/hammer-indent-crimper.html

Re: Battery interconnections

Windsun that sems like an ok tool . never seen one here in Aus only the very expensive professional use lever type.
You will notice that I tried to make it 100% clear that FIRST you need to make a good mechanical crimp BEFORE soldering. but it seems everyone missreads my saying that in every post by their replies as if im advocating solder only. IM NOT THAT IS HOPELESS AND FAILURE WILL MOST LIKELY RESULT UNDER HEAVRY LOAD
I try one more time,
MAKE A VERY GOOD MECHANICAL CRIMP FIRST THEN TEST THEN SOLDER LAST.:cool:

Re: Battery interconnections

Here is the results of resistance testing and mechanical destruction testing of lugs on copper wires as used in battery interconnects and similar usage.

A total of 10 lengths of copper water pipe was purchased from hardware and plumbing supply stores. The 2 sizes purchased had inside diameters or 1/2 "(12.5mm) and 3/4" (19mm) thickness ranged from 1.25mm to 2mm. All pipe lengths were 10ft (3050mm)

Each size and thickness of pipe was purchased from a different supplier
All measurements were carried out on a calibrated desk multimeter.With a accuracy of+ or - .02%

1.1/2 pipe 1.25mm =.0012 ohms

2.1/2 pipe 1.25mm =.0013 ohms

3.1/2 pipe 2mm soft = .0008

4.1/2 pipe 2mm hard = .0009

5.3/4 pipe 1.5mm = .00065

6.3/4 pipe 1.5mm = .00061

7.3/4 pipe 2mm soft= .00042

8.3/4 pipe 2mm soft = .00041

9.3/4 pipe 2.2 hard = .00040

10.3/4 pipe 2.1 hard = .00039

As noted the resistance was given for 10ft lengths of pipe . If we are going to use any of those pipes as barttery interconnects etc obviously the length used would be about 8" to 10 ", so to get the resistance you would have to divide the above resistance figures by about 12.

To give worst case example the 1/2 pipe 1.25mm at .0013 ohms per 10ft divide by 12 =.0001ohms per foot
THe loss across that pipe used as a battery interconnect would be using 24v connected to a 100 amp load = 40ma
Now lets see how that compares to using a #2 cable and 2 lugs cable resistance = .00052 plus 2 crimped lugs at .00046 total resistance = 99ma loss

Any talk about wondering about losses for 1000 ft of ANY 1/2" copper pipe can clearly be shown to be a pointless exercise. and it way surpasses using #2 cable and the fact is most people would only be using #4 cable as interconnects.With far far greater losses.And as I said in a much earlier post use 3/4 " copper pipe.No matterif it has many impurities its still far far ahead of #0 cable for battery interconnects

Tests involved to measure lug on wire resistance and mechanical strength.
the tests involve #4 cable and closed ring closed tube copper lugs 2mm thick

1.Lug compressed with 500lb pressure on 3 serrated teeth jaws. resistance .00023 ohm.Lug then tested for breakaway

.seperated from cable at 223lbs pull

2,Lug compressed with 500lb pressure on 3 serrated teeth jaws then lug heated and filled with resin cored solder.

resistance .00015 seperated from cable ..failed as cable broke before cable seperated . test pull 325lbs

3. lug and cable resin cored soldered only. resistance .0008 seperated from cable at 127 lbs

As you can see solder only is not good. As a further test the joint melted when a 140a load was connected to the cable and a 12v battery to the lug. Obviously not good.

As you can see I didnt get much work done for employer the day I did all these tests, believe it or not it took 3 of us to do the tests .my work partner to verify the results ..As to do any destructive testing a workplace safety officer has to be present.
Hope some of this helps people understand a little more about cables lugs copper pipes..:cool:

Re: Battery interconnections

Now lets see how that compares to using a #2 cable and 2 lugs cable resistance = .00052 plus 2 crimped lugs at .00046 total resistance = 99ma loss

If you used #2 interconnects around here you would get beat at the least. 2/0 interconnects on my bank!

Re: Battery interconnections

Niel .Audridgers reply is not correct. as if he used 8.3/4 pipe 2mm soft = .00041 (not the best one but average)it has a resistance on a 1ft length of .000034. that is still going to be a lot lower than if he used 2 parallel runs of #0 cable as the cable lug connections have a higher resistance than that even if he used a cable with almost zero resistance. And thats difficult to find even if you run the cable in liquid nitrogen.

I think what the whole testing did was show the lug/cable connection is the weak link when you get to cables above #4. and it did prove adding solder into the lug does help both the mechanical and electrical connection.

Re: Battery interconnections

My point was and still is even 2 parallel runs of #0 cable or 4 runs of parallel #2 cable is going to have more resistance than 3/4x 2mm copper pipe.

As for using cable to better absorb "earthquake" shakes I dont think you would find much in flex with 6" of #0 cable. You will notice all electric vehicles use solid connections between battery cells. why? only half the number of connections. Also military radiotrucks have all the FLA batteries with solid copper plate connections and they are designed to travel over very rough ground and keep working. So by comparison any vibrations in a house is not going to be a problem with solid battery connections, I would be thinking if the "house shaking" is that severe you more likely to be worried about the house collapsing rather than the batteries vibrating and loosening their connections.

Re: Battery interconnections

Point taken. Think I'll keep the cables that I have though.

Re: Battery interconnections

Audredger I notice you using a 4000w inverter and 24 x6v batts. most likely connected as 6 strings of 4 batts per string??
If surge rating of say 5000 watts is taken as max . and about 90% efficient that would be a max current draw of about 230a. Therefore if 6 string of batteries a bit under 40 a per string. A #2 cable has a 20deg c rating of 160 a. IF you were using #2 cable as interconnects you would only be still using avbout 1/4 of their capacity.
Dont know what you are using between batteries and inverter but #0 cable only has a rating of 200a a little shy of what your max current draw could be. But if only about 2ft long its most likely ok.

John, yes 4 L16H 6 v tied together with 2/0 to make a 24 v bank; 100 amp fuse at each bank and #2 cable from fuse to 600 amp bus bar; 4/0 cable from bus bar to inverter breaker and then to inverter.

BTW all my wire is oversize. I try to keep the line loss to <1%. Tough enough to generate it to loose it as line loss!

Re: Battery interconnections

John, not #4 but 4/0 (0000); 11.68 mm not 5.18 mm ... 2/0 (00) is 9.2 mm. BIG welding cable