Battery interconnections

mike95490

Re: Battery interconnections

I had to create my own lug adapters for my giant battery terminals, I used underground rated, 3/4" copper pipe,
tinned inside and out, and again after being flattened and formed for the bolt on lugs, using SS bolts.

http://tinyurl.com/LMR-BigLug


Mike

NorthGuy

Re: Battery interconnections

mike95490 wrote: »

I had to create my own lug adapters for my giant battery terminals, I used underground rated, 3/4" copper pipe,
tinned inside and out, and again after being flattened and formed for the bolt on lugs, using SS bolts.

I used a piece of copper pipe to connect my shunts, but then I didn't like it and replaced it with cable:

john p

Re: Battery interconnections

NORTH GUY I see the two photos they both seem ok to look at so why you feel the need to change from the copper pipe to cable?? Please dont tell me its because its easier for the shunts to move around. The actual exposed(outside the lug)cable looks to be about 5mm or about 3/16th inch. ????!!!!

Its 2 connections less for using the pipe.

NorthGuy

Re: Battery interconnections

john p wrote: »

NORTH GUY I see the two photos they both seem ok to look at so why you feel the need to change from the copper pipe to cable?? Please dont tell me its because its easier for the shunts to move around.

The flaps were about 3-5 degrees out of alignment and the pipe was very rigid. I felt that I may not be getting a good enough contact.

john p wrote: »

The actual exposed(outside the lug)cable looks to be about 5mm or about 3/16th inch. ????!!!!

It's #3 copper wire between the lugs.

Cariboocoot

Re: Battery interconnections

Well I would have used flat stock for the shunt connections because it's all fixed location and nothing is going to move and there's no possible interference from anything. Measure, drill, done.

As John says, the solid connectors eliminate the joint between wire and lug (he and I seem to be the only two who prefer crimp and solder on these) and is a consistent low-resistance connection.

The main reason I pick cables on batteries is because of their flexibility; most people would have trouble making their own solid bar connectors and getting them right. Heck I've seen cables not tightened down properly because "they didn't want to damage anything". How's that for irony?

Panamretiree

Re: Battery interconnections

NorthGuy wrote: »

I used a piece of copper pipe to connect my shunts, but then I didn't like it and replaced it with cable:

NG - I thought shunts were engineered to do a specific task so I googled it and found:

"A shunt is necessary in order to measure amps and amp-hours with battery monitors. A shunt is a very low resistance accurate resistor which is placed "in line" with the wire carrying the current to be measured. Because there are frequently several taps driving power in and out of the positive battery post it is best to place the shunt on the common negative lead so that all charging and discharging current must pass through the shunt. The shunt must be placed near the battery array because these wires carry very high currents the wires from the batteries must be kept short to minimize electrical losses."

and

"As current flows through the shunt, a small voltage is developed across the shunt which is proportional to the current flow. The battery monitor measures this very low voltage and converts it to the Ampere reading on the meter. A shunt is rated by the maximum current that can safely flow through it. The higher the current that flows through it the greater the temperature rise of the shunt. Using too small a shunt will cause permanent damage by changing the resistance properties of the shunt or even fire if the current is excessive."

Having found these, what is the rationale for using copper pipe to connect shunts, or cable for that matter. Would one not have to know what the resistance of the connection was to make sure that everything worked properly. I looked at the Trimetric 2025 installation instructions and it specified/recommended a 500A/50mv size shunt. If you were to not use a recommended sized shunt, would not your readings be skewed, and not accurate?

Never thought of making one.

Cheers

Ernest

Cariboocoot

Re: Battery interconnections

Shunts are often connected together - on one side. Then one is used for measuring current going in to the battery and the other to measure current going out of the battery. Or any other combination of checking power flow on two different lines.

He probably does not have them connected in parallel (both sides) as it would be rare indeed where that would afford any advantage.

BB.

Re: Battery interconnections

Two definitions of SHUNT:

1) a short piece of metal or cable to make a connection (or shunt/bypass around a piece of electrical equipment).
2) typically a high power precision resistor placed (typically) from the negative battery connection to the shunt to the negative battery bus. So that all battery current flows through the precision resistor. There are two connections on the side of the resistor where a voltage meter is attached (to measure voltage drop across the shunt--Also known as Kelvin contacts)


The top posts are for the heavy current wiring. The two screws on the side are where you attach the "volt meter" (or battery monitor) wiring to measure the voltage drop.

So, you can connect "shunts" together with "shunts". (precision resistors together with short cables/copper bus bars).

-Bill

NorthGuy

Re: Battery interconnections

Panamretiree wrote: »

Having found these, what is the rationale for using copper pipe to connect shunts, or cable for that matter.

Here's the final assembly.

On the bottom right is the cable coming from battery negative. On the bottom left is the cable going to inverter. So, the bottom shunt measures inverter current.

On the top left are two cables coming to MPPT controllers. So, the top shunt measures solar charging current.

Panamretiree

Re: Battery interconnections

NorthGuy wrote: »

Here's the final assembly.

On the bottom right is the cable coming from battery negative. On the bottom left is the cable going to inverter. So, the bottom shunt measures inverter current.

On the top left are two cables coming to MPPT controllers. So, the top shunt measures solar charging current.

Got it. Nice setup.

Cheers

Ernest

NorthGuy

Re: Battery interconnections

Cariboocoot wrote: »

Well I would have used flat stock for the shunt connections because it's all fixed location and nothing is going to move and there's no possible interference from anything. Measure, drill, done.

I wanted to do that too, but I didn't have a flat stock, only had a pipe. Could've cut it along and flatten it as Mike did, but this idea didn't come to me at a time I did have two lugs, so I used them to make a micro-cable. It does look good

Panamretiree

Re: Battery interconnections

NorthGuy wrote: »

It does look good

You have an artistic flair for design, very pretty:-)

Cheers

Ernest

john p

Re: Battery interconnections

Shunts are your best friend in a solar system and for that matter any battery system. A shunt gives you so much useful information about how well your system is running.
When you system is all ok you just either write down or remember what readings you get then in future you just look for any differences between the readings,providing of course the system is still the same and powering the same items..
Its the ability of a shunt to show different readings over time that makes it so easy to find a developing fault,like a bad battery terminal connection or a powered item wearing out and drawing more power.

I think it should me mandatory to use them between battery and panels and between battery and inverter. They are the ONLY item that will accurately tell you how much power is drawn by any device connected to an inverter. it takes into account different efficiency and wave forms of the inverter.

The following are my personal views on shunts and why they are so superior to fuses or circuit breakers. If you dont agree thats ok by me.
A shunt is better than a fuse/circuit breaker. ? Why?
But before I say Many experts will tell you this"A shunt is a precision resistor and not ok to use as a fuse" This to me is writing before thinking .!!!
Its the very fact as they tell you that it is a precision resistor that makes it better than a fuse.
Why?
Because they are laser trimmed they have a very predictable fail point.
A shunt will have results something like this
100% of its rating will function almost indefinitely
120% of rating fail in 40mins
130 % of rating fail in 15 mins
150% of rating fail in 5 mins
180% of rating fail inside 5 seconds
Now a circuit breaker is designed with very wide tolerance and go open circuit at between 70% and 200% of its rated load .And are greatly affected by ambient temperature. very unpredictable.
Their other problem is sometimes the an ark can be maintained between the contacts so power is still getting past the circuit breaker. Shunts by comparison usually have all the metal completely melt so there is good distance now between the terminals.No possibility of "arc over"

A shunt will do something a fuse or circuit breaker cant ever do is show you when an overload is starting to happen. It may be the powered device is wearing out.or it may be overloaded in some way. This gives early warning of impending failure and gives you a chance to rectify the problem.
It can show if there is now a bad connection somewhere that may not be easily seen.

By watching the shunt readings you soon get to know what they should be and if something out of the norm is happening

Simply put shunts are your best friend in a battery system and cheap and with extreme predictable results of the power drawn or supplied through them.. The 50a and 100a ones are the most useful. Dont buy a 500a shunt unless you really are going to go over 1200w in that part of the system..ie(12v x 100a) as the readings for say 20a are very hard to do accurately. You only need a cheap multimeter or a millivolt meter to read the voltage across the shunt..
NAWS or other similar solar suppliers can supply the items .
Happy shunting

Cariboocoot

Re: Battery interconnections

The thing about not using shunts as fuses is: it won't pass inspection because a shunt is not listed a circuit protection device.

Argue with Mr. Wiles if you like. We all do from time to time.

BB.

Re: Battery interconnections

And for new readers-- John P does a lot of testing of power related equipment (that is his job--blowing stuff up).

So, his experience on shunts (for example) is based on a number of laboratory tests and he has come to his conclusions based on those test results. The shunts as fuses do sound more accurate than breakers and normal fuses (they have very wide trip ranges and can be very temperature sensitive--depending on the type of breaker/fuse).

As long as the shunt is not mounted on wood or over a wooden floor (i.e., sheet metal or metal screening to capture burning bits) -- It may be a good alternative to buying big fuses.

One question for John--Did you get a chance to try "maximum interrupt" current testing (i.e., 1,000/10,000/+ amp sources) to see how the shunts behaved?

DC current is great for "arc welding" and is very difficult for fuses/breakers to interrupt at higher voltages and current levels. So, dead shorts on a DC battery bus can be exciting.

-Bill

Panamretiree

Re: Battery interconnections

BB. wrote: »

The shunts as fuses do sound more accurate than breakers and normal fuses (they have very wide trip ranges and can be very temperature sensitive--depending on the type of breaker/fuse).

As long as the shunt is not mounted on wood or over a wooden floor (i.e., sheet metal or metal screening to capture burning bits) -- It may be a good alternative to buying big fuses. -Bill

Bill - good concept, but how would a manufacturer take to its equipment being protected only by a shunt that in NA is used mainly for getting readings from a system, especially if there is a warranty issue?

Since I live in the Republic of Panama, and have seen no code books of any kind (you don't want to know or see how they do some electrics down here) maybe a good option for some of my install.

Shunts may be easier to source than breakers.

Cheers

Ernest

Cariboocoot

Re: Battery interconnections

I doubt manufacturers would consider a shunt as an over-current protection device either.

The irony here is that the shunt works well for this because it is precision-made; it would not work as a shunt if it weren't. Whereas fuses and breakers have manufacturing tolerances much greater than a shunt, so their resistance/current handling/reaction time has a larger variance.

Now if they'd like to make some precision fuses ... oh wait, they do (or used to). Cost a lot more than the ones that are "good enough".

Cariboocoot

Re: Battery interconnections

Just to clarify, you can't legally use a shunt in place of a fuse.

But there's no reason at all that you can't use one in series with a fuse to satisfy the legal aspect. In fact I think this is what John is recommending. To say nothing of his point on them being the way of getting accurate current measurements!

NorthGuy

Re: Battery interconnections

Cariboocoot wrote: »

But there's no reason at all that you can't use one in series with a fuse to satisfy the legal aspect. In fact I think this is what John is recommending. To say nothing of his point on them being the way of getting accurate current measurements!

I've never thought about using shunts that way, but the melting down values that John posted are very reasonable, so it most likely will work. If current is very high, it might arc in the process of melting. So it better be in some kind of fire-resistent box.

For the accurate current measurement I would go with a shunt with higher A rating, because it will dissipate more heat and will not heat up under working current. If you go with lower rating, it'll be routinely warming up and cooling down as the current changes. The resistense of the shunt depends on the temperature. Therefore, by letting the temperature vary, you introduce temperature-related errors and decrease overall occuracy.

Panamretiree

Re: Battery interconnections

Found a primer on "Understanding Overcurrent Circuit Protecters" at:

http://www.ieee.li/pdf/viewgraphs/overcurrent_protectors.pdf

More information for us who do not want to "reinvent the wheel", but "go with the flow".

Looking up this information reminded me of my strength of material teacher at the Marine Institute in St John's, NFLD, who walked into class one day and asked if, when we were out driving and saw the streetlights, ever wondered how they stayed up and did not fall down. It was a unanimous "NO", and on that note, he proceed to lecture us on the how and why.

Cheers

Ernest

Cariboocoot

Re: Battery interconnections

*Quick check of memory: no, never taught in NFLD*

*Whew!*

Blackcherry04

Re: Battery interconnections

Let's see, Inverter $1,800, Shunt $50.00, Class T Fuse $26.00. Even if it did work, it's hardly a economic value. The laboratory in my shop tests many thing to destruction the cost usually comes out of my pocket.

vtmaps

Re: Battery interconnections

NorthGuy wrote: »

If current is very high, it might arc in the process of melting. So it better be in some kind of fire-resistent box.

Even if it doesn't melt and arc it should be in a fire resistant box. Shunts can get quite hot even when used within their ratings. --vtMaps

john p

Re: Battery interconnections

Its good to see members do read and comment on these posts.. Its how we all learn.
To answer some of the questions.
BLACKCHERRY 04 im not sure what the connection is with the $1800 inverter.?? If you are paying $50 for a shunt below 500a I suggest you shop elsewhere.
At26 fuse is no more accurate than other types of fuses.
As I have no idea where you all live cant give on here what is legal or not legal to use. But for most people using a solo battery system there would be few legal issues. But if you want to use shunts for their advantages then if for legal reasons you also need to add a fuse/circuit breaker then I suggest you use the highest value fuse/circuit breaker that you can legally use.. This way it will be the shunt that fails first. and hopefully will show you what was the cause of failure.
After extensive testing I have found that shunts keep their rating even when very hot.That can be proved as they can hold rated current almost indefinitely and still only fail at about 180%

Blackcherry04

Re: Battery interconnections

john p wrote: »

Its good to see members do read and comment on these posts.. Its how we all learn.
To answer some of the questions.
BLACKCHERRY 04 im not sure what the connection is with the $1800 inverter.?? If you are paying $50 for a shunt below 500a I suggest you shop elsewhere.
At26 fuse is no more accurate than other types of fuses.
As I have no idea where you all live cant give on here what is legal or not legal to use. But for most people using a solo battery system there would be few legal issues. But if you want to use shunts for their advantages then if for legal reasons you also need to add a fuse/circuit breaker then I suggest you use the highest value fuse/circuit breaker that you can legally use.. This way it will be the shunt that fails first. and hopefully will show you what was the cause of failure.
After extensive testing I have found that shunts keep their rating even when very hot.That can be proved as they can hold rated current almost indefinitely and still only fail at about 180%

Is Shouting out my name out some form of self validation JOHN P ??

john p

Re: Battery interconnections

Long before Istarted to recommend using shunts at work instead of circuit breakers Ihad spent months doing comparison tests between them. Iended up with a huge amount of data most of it was not even aware of.And it seemed most others werent either including all our engineers.But even with all this data got nothing but big laughs from all tecs and enginers until I showed some practical tests. They had never seen tests done like this . It seems we just use a fuse or circuit breake about the size we think is correct for the device it needs to protect and thats it.

Its only when testing them I found just how inaccurate fuses and circuit breakers were.Testing with voltages just below their rating with 200% current rating many failed to break the circuit at all. Many failed only when the connecting wire to the breaker terminal melted.

Breakers and fuses change their fail point far greater than shunts do.. I dont know what metal is used in shunts but even with full rated current and hot they act still very similar to when only just warm..

If you have used shunts you will have noticed that when they do fail there is very little molten metal that falls from them,.It just seems to vaporize. Which is good. So good we only mount them on nylon household cutting boards. Cheap.. And have never had a problem.

The highest voltage and amperage I ever put through a 500a shunt was 480v (its the biggest battery bank we had)and about 800a..this was the test that amazed the engineers. as the circuit was broken perfectly and instantly. And no metal to be found to cause a problem. This is as good a result as you will get with a circuit breaker costing over $1000.

In reality there seems to be a good reason that its hard to find shunts rated above 500a. And really this is to high in my opinion. You should be using a clamp on ampmeter for these amperages.I dont like the 2 extra connections that a shunt uses.

At work my idea was given the go ahead for a 3 month trial .That was over 5 yrs ago.And no problems. Its very easy to remote mount as many millivolt meters as you need to see the functioning of the complete battery,generator,charge controller and inverter and the powered device.

I also cant see how there could be any problem with warranty on any device that used a shunt as the protection of that device. In fact they behave better than fuse/circuit breaker.

When I did all the comparison tests it was a bit of a let down as didnt have much in the way of expensive destroyed items to display..so sad really.

Getting a grid tie inverter to sync with a battery inverter not designed for doing so was a far greater fun day as had 3 grid tie 1500w inverters and 3 x 1000 w battery inverters destroyed.. a much more productive day.. but success did happen using the 4th 2 inveters..But then had to on company rules destroy them as they had "dangerous" modifications.thats life.

john p

Re: Battery interconnections

Sorry blackcherry04 I only did it so it easier to notice.. Not done with any other intention.. Im again sorry if it offended you. I wont do it again.

Cariboocoot

Re: Battery interconnections

The reason being that a shunt is highly stable in its value across temperature and current whereas your average fuse/breaker is not.

For comparison purposes:

NAWS sells a 100 Amp shunt for $24: http://www.solar-electric.com/mka-100-100.html
500 Amp for $27 http://www.solar-electric.com/mkb-500-50.html

110 Amp fuse with holder is $45 http://www.solar-electric.com/fb-110t.html

It would be nice if those fuse holders (which have covers) could be adapted to hold the shunt.

Again the issues are: passing inspection (where required), satisfying equipment manufacturers' requirements for circuit protection (they would not recognize a shunt as CP), and preventing fire in the event of a failure.

As with grounding, if the system is designed right and no accidents occur you never know whether or not your CP is right because it only works when it fails!

Panamretiree

Re: Battery interconnections

NorthGuy wrote: »

Here's the final assembly.

On the bottom right is the cable coming from battery negative. On the bottom left is the cable going to inverter. So, the bottom shunt measures inverter current.

On the top left are two cables coming to MPPT controllers. So, the top shunt measures solar charging current.

NG - have a query regarding your "shunt" and current measuring setup - just thought about it today as a matter of fact. The bottom shunt in your picture measures inverter "in" current, but would the XW6048 not provide this information, or is this a double check on the system? Second is the top shunt that measure solar charge current, should this not be provided by your XW 60 CCs with the same caveat as per the first query?

Cheers

Ernest

inetdog

Re: Battery interconnections

Panamretiree wrote: »

NG - have a query regarding your "shunt" and current measuring setup - just thought about it today as a matter of fact. The bottom shunt in your picture measures inverter "in" current, but would the XW6048 not provide this information, or is this a double check on the system? Second is the top shunt that measure solar charge current, should this not be provided by your XW 60 CCs with the same caveat as per the first query?

There is some potential advantage to using either the same meter or an identical accurate meter to measure the voltages on both shunts. If there is an error it is likely to affect both similarly.
With CCs and inverters it is not clear what the accuracy of the voltage display is or how it correlates to an external meter or an internal meter on other equipment.

If you are using a networked digital meter for this purpose, both current values are easily accessible to a computer-based monitoring program, without having to worry about the comm protocols of several different devices.

And if you want to know the net current in or out of the battery, direct measurement with a shunt is better than subtracting two large numbers from different sources to get a small number.