Load and heat

[weq92f]

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So...I've got this bus bar where everything connects. All the power grabbers and the power adders (alt, batt) all connect to the bus bar.

While playing with my fan setup today I happened to notice my bus bar has some heat in it at full load (elec fans, A/C, blower on high, lights on bright). Measured the heat at about 150F on the bus bar. I was feeding the bus bar from batt with 4AWG but changed that to 2AWG today. After doing this I had more total voltage at the batt than before (14.5VDC) so I'm sure the 4AWG cable wasn't enough, however the heat in the bus bar didn't really change.

The bus bar has these ratings:

* Continuous amperage of 130 amps AC, 150 amps DC
* Maximum voltage rating 300 V AC, 48 V DC

My alt is 140amp and my estimate of the amperages being pulled through there were below 150, the max rated for this bus.

What are your thoughts on this heat...I'm sure it's been running this way since the day I rewired everything. All power leads off bus bar are fused with either in line or fusible link.

-Kevin

[Dead Parrot]

Is there a temp spec with the buss bar? If the bar is in the engine compartment, under hood temps are probably higher then 150* anyway.

If the buss bar terminals allow, might move the heaviest load to the same terminal as the Alt wire so that load isn't flowing through the bar. Put the heavier loads in the middle with the alt and the lighter ones on the outsides. Minimize the bit of bar carrying the heaviest load.

[weq92f]

Originally Posted by Dead Parrot

Is there a temp spec with the buss bar? If the bar is in the engine compartment, under hood temps are probably higher then 150* anyway.

If the buss bar terminals allow, might move the heaviest load to the same terminal as the Alt wire so that load isn't flowing through the bar. Put the heavier loads in the middle with the alt and the lighter ones on the outsides. Minimize the bit of bar carrying the heaviest load.

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I'm not finding a temp spec for it. I'll rearrange the leads in this manner as it does seem logical. I'm running 6AWG from the alt to bar which I believe should be adequate.

Good point about the engine compartment heat however I'm certain the leads also have a bit of heat in them...at least the heavy electric fan leads to the relays do.

Thanks much,

-Kevin

[weq92f]

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I placed the 3 electric fan leads along with the Alt lead on the same lug in the middle of the bar and distributed the remainder on the other lugs. This changed things for the better in terms of how the system reacts to high draw fans kicking on and the in dash volt gauge now reads much closer to actual at-the-battery volt readings. This gauge thing may have been the result of changing the 4AWG batt to bar cable to 2AWG.

Thanks again,

-Kevin

[87chevy.com]

are the terminals on the wires crimped properly? if not, that could be causing the issue.

[weq92f]

Originally Posted by 87chevy.com

are the terminals on the wires crimped properly? if not, that could be causing the issue.

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I’m no expert but these are all 10 and 12 gauge with crimped terminals. I used appropriate sized noninsulated ring terms and tried to curl the seam down into the wire strands with the right crimper. Shrink wrap. Shoulda soldered the big ones.

Next time I’m there I’ll check the heat at those connections.


Thanks!

-Kevin

[Orange Crate]

Pictures?

[kwmech]

Under hood temps this time of year I'm sure will approach the 200+ degree mark. If you are below the AMP rating of the bar I wouldn't worry about it as long as everything is crimped, soldered and tight. Which buss bar bar are you using?

[weq92f]

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This is the one I have installed. It is about 7" long and beefy.

https://www.summitracing.com/parts/qdb-568102

-Kevin

[weq92f]

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OK well I've found the limit on my electrical system at idle. 103 outside temp while idling, my system lags bad. I can hear the interior fan slow and if it were at night I'm certain I would have seen my lights dim. Going neutral and raising the RPM to 1100 or so remedies the situation...mostly.

I'm sure it's a combination of engine compartment heat and either an alt that can't handle the load or the lead wire off the alt to the bus that isn't big enough.

I estimate 70 to 80 amps were being demanded on the bus bar when things went sort of south as described above. My 140A alt should be OK but I can't find an idle output spec for it so ~maybe~ not. It's single post has a 6AWG wire going into a 10AWG fusible link to the bus.

I'm wondering whether 6AWG is enough. According to the wire chart, it ~might~ but without the really high operating temp accounted for.

I would like to update the alt to bus wiring to 4 or even 2 gauge to just make sure. The run from alt to bus is about 4ft.

What are your thoughts?


Thank You!

-Kevin

[Orange Crate]

Originally Posted by Orange Crate

Pictures?

Somebody famous once asked the above....I'm asking for pictures of YOUR set up that you actually have under the hood.

[Dead Parrot]

I think I read somewhere the most alternators produce their rated output at 6000RPM. That is Alt rpm, not engine rpm. You will have to measure your drive and driven pulley sizes to see what engine rpm = 6000 alt rpm.

Unless you have some special low speed alt, you most likely are not getting anywhere near 140A at engine idle. That is why things perk up when you rev the motor.

What is the battery cable size? Since it has to cover any shortage from the alt, any voltage losses in the cable will matter. The alt normally has a remote voltage sense wire(unless it is a one wire), that will cover losses from the output terminal to the buss bar.

[weq92f]

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Went to take pictures of it today and ended up learning that my phone is lost. Go figure.

Batt to bus bar is 2AWG with a 3ft run. Haven't found the idle spec on my Alt yet but I do know its not the rated max amperage. Should be 30-50 methinks. The Alt is a 1 wire unit.

I adjusted my idle up 100RPM which does make me feel better about it.

-Kevin

[Dead Parrot]

Eeek on phone!

What about the negative cables? If your negative batt cable is long, there might be a small benefit to going up one size. It has to carry the same current the positive one does.

Also, make sure all the grounds are a decent size. A #2 wire from the block to frame would make sure the ground side of the alt output has an easy path. If your main ground is that flat cable from the valve cover to the firewall, your load might be overloading that cable.

Maybe create a ground lug connection. A bolt thru the frame where both batt and engine ground meet.

[weq92f]

Originally Posted by Dead Parrot

Eeek on phone!

What about the negative cables? If your negative batt cable is long, there might be a small benefit to going up one size. It has to carry the same current the positive one does.

Also, make sure all the grounds are a decent size. A #2 wire from the block to frame would make sure the ground side of the alt output has an easy path. If your main ground is that flat cable from the valve cover to the firewall, your load might be overloading that cable.

Maybe create a ground lug connection. A bolt thru the frame where both batt and engine ground meet.

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The Alt is grounded with a 4AWG cable to the frame. This also acts as block to frame ground. Batt is grounded also to frame through a short 2AWG cable.

I'm going to order a larger alt lead, install that and send it. If things are still at the edge, I'll upgrade the Alt.

Yeah, after adjusting the throttle blades and idle I went for a test drive. Either I left my phone sitting someplace on the outside of the truck or in the engine bay. Haven't seen the phone since. Second time I've become separated from my phone in a single year.

-Kevin