How close can bare copper bus bars be (12v)

noenegdod

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I am using 1.5"x1/4" copper flat bar for a portion of the system. This portion of the system will supply about 600 amps to a winch. There are 2 BP220 that will share the load. The picture below is obviously of one but the flat bar will run across both of them in this direction. The right side is 2 inch FB but is just there for illustration. In practice it will be 1.5" The gap is almost 3/16".

This is not a short circuit risk as both bars are positive. My concern, based on ignorance, was if I was to get a short downstream while the BP are open, is it possible that 13.5 volts could under any circumstances jump that gap? I can easily install an insulator between them, just wondering if that is necessary.

20211026_203053.jpg
 

rmaddy

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Ignoring the actual question for a moment. How do you hope to have two 220A battery protects (440A total) supply 600A of power?

For a 220A (even 300A) load you need 3/0 wire. The rough equivalent in 1/4" copper bar would be about 9/16" wide. Using 1-1/2"x1/4" is much larger than necessary.
 

noenegdod

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Ignoring the actual question for a moment. How do you hope to have two 220A battery protects (440A total) supply 600A of power?

For a 220A (even 300A) load you need 3/0 wire. The rough equivalent in 1/4" copper bar would be about 9/16" wide. Using 1-1/2"x1/4" is much larger than necessary.
Peak current for each one for 30 seconds is 600 amps: https://www.victronenergy.com/uploa...rt-Battery-Protect-65-A--100-A--220-A-EN-.pdf

Yup, it is larger than required. for a few inches of copper the cost difference between what is required and overkill is marginal. I always prefer to overkill if a) I can afford it and b) it has no downside.
 

Rocketman

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Get some insulation on those bars - heat shrink - if you find it big enough to go over it. There is also liquid electrical tape - or real electrical tape - just something.

You do not want to drop a screwdriver while working on something else and create an arc welder. Prevent bad days.
 

rmaddy

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Yup, it is larger than required. for a few inches of copper the cost difference between what is required and overkill is marginal. I always prefer to overkill if a) I can afford it and b) it has no downside.
Agree but my main point was that you can make them a bit narrower thus giving you a much bigger gap between them.

As has been stated by others, insulate them or a dropped tool, screw, bolt, etc. could be quite exciting.
 

noenegdod

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You do not want to drop a screwdriver while working on something else and create an arc welder. Prevent bad days.
As has been stated by others, insulate them or a dropped tool, screw, bolt, etc. could be quite exciting.
As I said above, there is no short hazard inherent here. Both bars are positive. They are simply on opposite sides of a switch. The question was more in regards to if there was an issue down stream with a short, would there be any chance what so ever of an arc jumping at that point.
 

Bud Martin

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Since the Winch is basically an inductive load, it will have quite a big kick back Voltage (back EMF) when the BP goes open circuit (MOSFET is turned off), I wonder how well the BP can handle it. I would ask Victron to hear what they'll say about your application.
Some info about Back EMF:
 

noenegdod

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Since the Winch is basically an inductive load, it will have quite a big kick back Voltage (back EMF) when the BP goes open circuit (MOSFET is turned off), I wonder how well the BP can handle it. I would ask Victron to hear what they'll say about your application.
Some info about Back EMF:
Crap. I had not considered that. I considered the start up current but not the field collapsing.

On the bright side, the BP does not control the winch. It is there to provide a convenient way to isolate a circuit that has the potential of mechanical damage. It will basically be off whenever I am not winching. But, there is a definite possibility the BMS will turn it off while in use if the battery gets to low.

I will definitely reach out to Victron and find out. Thank you for the heads up.
 

noenegdod

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I guess I should ask @Bud Martin or anyone else, do you have a recommendation for a clamping diode. I have a big 300 amp diode for a different purpose but can you recommend something for this application? I am well out of the "enough knowledge to be dangerous" zone on this one.
 

Bud Martin

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I would wait and see what Victron will say.
Does the Winch work in both both directions?
Any info you have about the Winch?
 

Will Prowse

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There has to be a better way.
Since the Winch is basically an inductive load, it will have quite a big kick back Voltage (back EMF) when the BP goes open circuit (MOSFET is turned off), I wonder how well the BP can handle it. I would ask Victron to hear what they'll say about your application.
Some info about Back EMF:
Yeah, this is the first thing I thought of as well. You will burn out that battery protect.

Considering how expensive a battery protect is, and the current you need, maybe build a small LTO pack? And use a small converter to charge it manually? LTO grade b cells would work great for this, and work in freezing cold conditions.

Or use a flooded cell lead acid. That is most cost-effective method, and it will power those winches.

I don't think a solar specific lithium battery running a large inductive load, controlled by a semiconductor switching device is ever a good idea. It might work for a few months, but it will fail eventually. The kickback can be massive.
 

noenegdod

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I don't think a solar specific lithium battery running a large inductive load, controlled by a semiconductor switching device is ever a good idea. It might work for a few months, but it will fail eventually. The kickback can be massive.
The BP is not controlling the winch. Current simply passes through it and when I am done using the winch I would just open the circuit to prevent any accidental shorts. The intent was to give the BMS the ability to control them though so it could disconnect in case of low voltage.

I didnt want to use LA because of space and weight. To run one of these winches for any more than a few minutes and get good consistent performance out of them you need at least 2 big LA batteries and even at that you start seeing big performance drops after just a few minutes. The lifepo4 battery supplying the winches is 1100ah so basically zero loss of performance during extended use.

I had considered LTO but was trying to not add another dimension to the system.
 

noenegdod

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To put it in perspective, with a 15,000lbs pull the winch is only spooling in 2.5' per minute. A tiny little 10' pull on that winch will pull 460 amps for a total winching time of 4 minutes. From personal experience, even with good Odyssey batteries the voltage really starts to drop off.
 

Bud Martin

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May be you should provide the wiring to show how you will switch the power to the Winch.
It sounds to me that the BP will normally be on all the time, but will be kept in off condition when the system is not in use but BP will go open circuit only during usage when the batteries Voltage is out off range, and you have another switch to control the winch on/off. Am I correct?
BTW, do you know what the stalled current (the surge current when power is first applied to the Winch) of the Winch is? Is it 600A as you mention in your first post? That means the power switch for the Winch has to be able to handle that too otherwise you can have welded contacts situation.
 

noenegdod

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May be you should provide the wiring to show how you will switch the power to the Winch.

It is obvious now that I have assumed far to much. I get pissed off at people for doing this and here it is I have done it myself. I have been off-roading my entire life and assumed everyone would know intrinsically what was involved with a winch.

The winch comes from the manufacturer complete. You physically bolt it to the vehicle and make the + and - connections and you are done. The winch comes with all necessary contactors attached to and wired in, and a remote. In my case the front remote is wired and the rear is wireless.

It sounds to me that the BP will normally be on all the time, but will be kept in off condition when the system is not in use but BP will go open circuit only during usage when the batteries Voltage is out off range, and you have another switch to control the winch on/off. Am I correct?

Correct! The 2 BPs will be used to energize the circuit but all switching on and off will be done using the winches integral controls. The one exception being if I draw the battery down to far the BMS will disconnect. This should be a truly rare occurrence because of the capacity of the battery. If I head out with a full battery I should be able to winch for 2 hours of actual winching time before it disconnects. Increasing that time is the 30 amps that the DC-DC will be supplying about1 minute winching time for every 15 minutes the vehicle is on and a generator mounted on the back I can start if things are getting out of control. Basically, the BMS should never have to intervene.

This circuit will also be used to jump start other vehicles and if I draw down the tiny LA battery I am using to start my own vehicle. For jump starting, connect to the other vehicle, Close the circuit, start the vehicle, open the circuit and disconnect. This should not be an issue for the BPs.

BTW, do you know what the stalled current (the surge current when power is first applied to the Winch) of the Winch is? Is it 600A as you mention in your first post? That means the power switch for the Winch has to be able to handle that too otherwise you can have welded contacts situation.
I do not know what the inrush current is. The 600A I had quoted initially was a mistake. For months I was planning around using 20k lbs winches which did draw up to 600a but it turned out I physically didnt have quite enough room for them, especially in the rear. I ended up keeping the 15 I already had and bought the new 12 (If I need more pull there is always a snatch block) for the rear which had the added benefit of the wireless remote which also has some accessory switches I can use to control turning the BP on and off through a relay, interlock style with the BMS .

So, all in all now that you have (I think) all the info, is this still an issue?
 

Hedges

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I guess I should ask @Bud Martin or anyone else, do you have a recommendation for a clamping diode. I have a big 300 amp diode for a different purpose but can you recommend something for this application? I am well out of the "enough knowledge to be dangerous" zone on this one.

The diode will spend most of its life (when winch powered) standing off battery voltage in reverse bias direction.
If FET switch opens it would briefly carry current in forward direction when inductor field collapses, and voltage swings from positive to negative.
Voltage will be clamped to a diode drop below ground. Current may multiply by something like 12V/0.7V so if 100A draw of winch it might spike to 1500A or so. Data sheet should show how long diode can take that. What we don't have is a good measure of energy stored in inductance, so not sure how long pulse lasts.

A silicon PN junction diode is better than a Schottky diode for clamping, because Schottky has high reverse leakage and can overheat, run away and short out. But, silicon junction diode is slower, could allow some spike through. Maybe if designing a product I would consider additional protection in parallel like MOV.

There could be other use-cases that produce other electrical surges. If winch is motoring out a load as it pulls away, in the case of a permanent-magnet motor, it might generate power of same polarity (rather than reverse polarity spike). If FET switch opened under those cases, diode still exposed to reverse polarity but could get over-voltage. Similar situation to wind turbine when load removed. Decide if this use-case is possible. (Maybe diode from winch motor to battery +12 lead would serve to clamp in that direction. In circuits to drive inductive loads, we might use two diodes to clamp to two supply rails.)
 

noenegdod

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The diode will spend most of its life (when winch powered) standing off battery voltage in reverse bias direction.
If FET switch opens it would briefly carry current in forward direction when inductor field collapses, and voltage swings from positive to negative.
Voltage will be clamped to a diode drop below ground. Current may multiply by something like 12V/0.7V so if 100A draw of winch it might spike to 1500A or so. Data sheet should show how long diode can take that. What we don't have is a good measure of energy stored in inductance, so not sure how long pulse lasts.

A silicon PN junction diode is better than a Schottky diode for clamping, because Schottky has high reverse leakage and can overheat, run away and short out. But, silicon junction diode is slower, could allow some spike through. Maybe if designing a product I would consider additional protection in parallel like MOV.

Would you mind giving post #17 a read and let me know if this is all necessary?

There could be other use-cases that produce other electrical surges. If winch is motoring out a load as it pulls away, in the case of a permanent-magnet motor, it might generate power of same polarity (rather than reverse polarity spike). If FET switch opened under those cases, diode still exposed to reverse polarity but could get over-voltage. Similar situation to wind turbine when load removed. Decide if this use-case is possible. (Maybe diode from winch motor to battery +12 lead would serve to clamp in that direction. In circuits to drive inductive loads, we might use two diodes to clamp to two supply rails.)

The motors are not permanent magnet motors. Not an issue then?
 

stienman

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If the Victrons disconnect while the winch is operating it is likely they will be destroyed, and an arc could form between that gap. Being DC, the arc will not be easily extinguished. Your loads nearly guarantee that the victrons will find plenty of opportunity to open due to low voltage conditions.

The copper bars don't really care about surge/starting current. They absorb the heat, dissipate it, and move on. Your loads count as surge loads, they are going to be running for seconds and minutes, not hours and days. So those bars are somewhat overkill for your needs. Further, you can probably accept an 80C temperature rise in those bars, so I'm expecting you have a whole lot more margin than you could need.

Lastly, offroading with this type of setup is simply not a good idea. The forces that will be placed on those bars as a consequence of vibration, twisting, compression, and other forces will ultimately physically damage the victron. You really need a flexible connection between components of this system, even if they're all mounted to the same 1/4" steel plate. If you manage it get them all on the same plate and within 3" of each other, with the plate only mounted to the vehicle at one point then you only have to face vibration, but even that's enough to cause problems over time.

So - yes, you can get away with them that close, and using the design you're thinking of, but there are a number of points where failure could occur that are easy to avoid at this stage of the design that you should spend some effort avoiding them altogether.
 
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