Is 140 degrees Fahrenheit too hot for bus bar?

[krfish]

Hi,

I have helped a friend build a really big battery setup for his RV. Here is the basics:

* 1800 Amps of 12 battery
* Victron Shunt
* Victron victron multiplus split phase

The question: when charging on city power, the inverter pushes almost 120 amps. The bus bar that is connected to the shunt gets to about 140 Fahrenheit after a few hours. We were cycling the battery for some testing, took quite a while to charge all the way back up (1800 amps - lol)

In any case, the bus bar never exceeds that temp and it take quite a while to get there. Seems normal, but I thought I would check with the community

Thanks!

 

[littleharbor2]

My guess, Either there is an untightened cable lug ,undersized mating surface on the lug or the bus bar is itself undersized for that current. Are the cables hot near the lugs?

 

[MisterSandals]

* 1800 Amps of 12 battery

Does your friend have another friend that knows battery capacities aren't rated in amps?
And perhaps that friend also knows how to size wiring to handle actual amps?

 

[sunshine_eggo]

I assume you mean 1800Ah of battery.

Base wire ratings are for 60°C or 140°F, and that's for the insulation. Bare copper can have much more.

Aside from the burn hazard, I don't see a problem PROVIDED you have confirmed all connections are properly torqued with associated crimps properly done, and no shrink caught in the connections. No washers are in the primary current path.

Worth measuring voltage across that bus bar to see if the voltage drop is acceptable.

 

[krfish]

I assume you mean 1800Ah of battery.

Base wire ratings are for 60°C or 140°F, and that's for the insulation. Bare copper can have much more.

Aside from the burn hazard, I don't see a problem PROVIDED you have confirmed all connections are properly torqued with associated crimps properly done, and no shrink caught in the connections. No washers are in the primary current path.

Worth measuring voltage across that bus bar to see if the voltage drop is acceptable.

Thanks! Yes, 1800Ah of battery, typed question fast. Technically there are 3 batteries capable of delivering 120 amps each. We have 4/0 wire, good lugs, etc. --- but the washer thing ... will have to go double check that one.

 

[krfish]

Just an update: Washers count! There was one washer in his system that he installed after the original assemble. That washer was a 3/4" washer. His goal was to level out the bus bar as he was unhappy with it not being quite level with the one it was attached to.

He replaced that washer with a 1" washer and all the heat problems went away. I took advantage of the opportunity to talk about current and surface area.

 

[sunshine_eggo]

Just an update: Washers count! There was one washer in his system that he installed after the original assemble. That washer was a 3/4" washer. His goal was to level out the bus bar as he was unhappy with it not being quite level with the one it was attached to.

He replaced that washer with a 1" washer and all the heat problems went away. I took advantage of the opportunity to talk about current and surface area.

If that washer is still in the current path, it should be removed UNLESS it's copper (maybe brass).Better to shim the bottom of the cell/battery to raise the terminal height than put a non-copper washer in the current path.

 

[OffGridInTheCity]

Connections (wire/lugs) from my charge controllers routinely run 55-60C / 131F - 140F in summer full PV within the master (metal) control box where they connect to midnite 80a breakers. This is warm to the touch but not 'hot' (not alarming) and the wire etc is all rated higher. So I don't worry and have set > 60C/140F as a red alert on my dashboard. I'm in year 6 and no obvious issues to date except of course heat = loss so I'm loosing some efficiency.

The heat comes from 4 x 4awg wires carrying 80a from the charge controllers to the bus within 2"? flex metal conduit over ~10ft. All installed by the original electrician presumably to code and passed city inspection.

I also have a heat sensor at the 120ft mark of combined PV wiring which is 4 x 6awg each carrying ~100v@50a within metal conduit and they approach 55C / 131F heat level in summer. So again, doesn't seem to be an issue except for efficiency loss because the wire is rated for this (also installed by the original electrician). It's interesting (to me) that the temperature increases as the distance get's longer from the PV array -> charge controllers.

 

[sunshine_eggo]

Connections (wire/lugs) from my charge controllers routinely run 55-60C / 131F - 140F in summer full PV within the master (metal) control box where they connect to midnite 80a breakers. This is warm to the touch but not 'hot' (not alarming) and the wire etc is all rated higher. So I don't worry and have set > 60C/140F as a red alert on my dashboard. I'm in year 6 and no obvious issues to date except of course heat = loss so I'm loosing some efficiency.

The heat comes from 4 x 4awg wires carrying 80a from the charge controllers to the bus within 2"? flex metal conduit over ~10ft. All installed by the original electrician presumably to code and passed city inspection.

I also have a heat sensor at the 120ft mark of combined PV wiring which is 4 x 6awg each carrying ~100v@50a within metal conduit and they approach 55C / 131F heat level in summer. So again, doesn't seem to be an issue except for efficiency loss because the wire is rated for this (also installed by the original electrician). It's interesting (to me) that the temperature increases as the distance get's longer from the PV array -> charge controllers.

don't want to argue, but I feel like you're really downplaying these as being "warm" temperatures as they are inconsistent with my experience and the larger body of guidance. Most hot water heaters are set to 140°F and less, and I don't think anyone would say that full hot water from the water heater at 140°F is "warm to the touch" when it represents a major scalding risk accompanied by substantial pain.

Here's a presumed reliable excerpt from an ASTM standard:

Surface Temperatures of Electronics Products: Appliances vs. Wearables | Electronics Cooling

by MP Divakar, PhD, Stack Design Automation Technical Editor, Electronics Cooling Online Prior to designing the requisite thermal management solution, engineers routinely calculate the junction temperatures of active and passive components using various methods at their disposal –finite...

www.electronics-cooling.com

ASTM C1055 (the Standard Guide for Heated System Surface Conditions that Produce Contact Burn Injuries) recommends that surface temperatures remain at or below 140°F. The reason for this is that the average person can touch a 140°F surface for up to five seconds without sustaining irreversible burn damage.

IMHO, something that will cause burn damage after 5 seconds is beyond "warm to the touch."

I'll grant that you may have a notably higher pain tolerance than the referenced "average" person, but I would not say your experience or position is "average," and I wouldn't rule out a potential measurement error as well. Your 140°F reading might only be 120°F, which would be more consistent with your description.

 

[Solarcabin Channel]

Maybe this will help:

"For safe operation with thermal reserve, it is advisable to limit the busbar temperature to a maximum of 85°C. However, the decisive factor is the lowest permissible continuous temperature of the components which directly contact the busbar system (fuse bases, out- going cables etc.)"

"What is the maximum temperature of copper busbar?


The maximum temperature is 140oC for copper busbars, 125oC for individual components (in accordance with the component manufacturer's instructions), and 105oC for external insulated conductors."

https://blog.se.com/infrastructure-and-grid/power-management-metering-monitoring-power-quality/2018/05/23/iec-61439-rated-current-of-electrical-panel-and-switchboard-protection-devices/#:~:text=The%20maximum%20temperature%20is%20140,C%20for%20external%20insulated%20conductors.

 

[OffGridInTheCity]

IMHO, something that will cause burn damage after 5 seconds is beyond "warm to the touch."

And I respect you and you're posts tremendously but the chart above is not correct based on what my Midnite Classic temp probes report and hands on experience. When I say warm to the touch I mean putting a finger on the wire and leaving it there indefinitely - no burn or anything close to it - just warm.

Maybe the Midnite Classic temp probes are reporting temps that are way off - could be. I would agree that anything too hot to grab indefinitely or that feels actually hot as apposed to warm - I would not want or feel comfortable with.

 

[ericfx1984]

Bro that's hot as Funk