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Old 08-21-2015, 11:02 AM   #21
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Which to me means that they could be different than "run" cables if the jumpers are less than 6 feet and the runs are longer...again...small patatoes but by suggesting that chart...then a series (jumper) cables of say 6 inches could be substantially smaller than ones at 6 feet.


That table really doesn't say much more than what I believe Kevin was saying and me that using loss and ampacity charts CAN be used to size jumpers...not arbitrarily using... "the same size as your "runs"" concept.....


But as has been said...do what you are gonna do....
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Old 08-21-2015, 11:23 AM   #22
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Originally Posted by psneeld View Post
Which to me means that they could be different than "run" cables if the jumpers are less than 6 feet and the runs are longer...again...small patatoes but by suggesting that chart...then a series (jumper) cables of say 6 inches could be substantially smaller than ones at 6 feet.


That table really doesn't say much more than what I believe Kevin was saying and me that using loss and ampacity charts CAN be used to size jumpers...not arbitrarily using... "the same size as your "runs"" concept.....


But as has been said...do what you are gonna do....
Exactly!

There is a huge difference between understanding the electrical and thermal properties of electrical conductors and quoting chapter and verse from a wire size table.

Again... I would probably not tend to undersize a battery jumper simply because I generally have the larger sizes and the crimpers on my boat all the time.

But It can be done and the loads would never know the difference.
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Old 08-21-2015, 11:42 AM   #23
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Hmm! That Trojan table doesn't match other ampacity charts I have seen/used. Look at Ancor's table here: Conductor Sizes | Ancor Ancor makes marine, tinned wire and also should know a thing or two about ampacity. Their table is consistent with others I have seen so maybe Trojan's is based on different conditions/insulation.


But back to the conversation. Sure if I were going to order a new jumper for my recent dual 6V battery installation, I would choose 2/0. But because my house bank will never see more than 220 amps and 99.999% of the time less than 20 amps, I used a #1 jumper that I had on hand. It works, and it is safe.


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Old 08-21-2015, 02:57 PM   #24
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Quote:
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Wire size tables are based on providing for a certain maximum voltage drop to the load.
Since wire size tables (as opposed to voltage drop calculators) typically do not reference the length of the wire run, that is not true.

Tables like the ones at Marine Wire and Cable: Voltage Drop Calculator are just based on the heat-dissipating capacity of the wire, which depends on its gauge, the temperature rating of the insulation, how many conductors are bundled together, and things like that -- all independent of length.

av8r and caltexflanc are correct about this.
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Old 08-21-2015, 03:03 PM   #25
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Since wire size tables (as opposed to voltage drop calculators) typically do not reference the length of the wire run, that is not true.

Tables like the ones at Marine Wire and Cable: Voltage Drop Calculator are just based on the heat-dissipating capacity of the wire, which depends on its gauge, the temperature rating of the insulation, how many conductors are bundled together, and things like that -- all independent of length.

av8r and caltexflanc are correct about this.
OK....how do YOU base what wire size to use on a run?
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Old 08-23-2015, 12:14 PM   #26
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Wire size short/long run

I had his same discussion with my marine electrician. We will likely increase cable size in my house bank to 4/0 when we rewire the bank for a more optimal configuration this fall. The "optimal configuration" change is to ensure the batteries in the bank contribute equally to the loads on the system. The reason for 4/0 is because of the length of the cable run to the inverter charger and the associated voltage drop when under large loading. Since the current cable size is 2/0, I asked if the connectors between batteries could remain at 2/0 since the current between the individual batteries would be considerably less than that of the mail cables to the inverter charger. He indicated that while that could be done, he urged best practice would be to switch everything over to 4/0 all the way to the inverter charger.


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Old 08-23-2015, 05:25 PM   #27
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Interesting, this is one of the few things in boating where you don't have to guess, follow an old wive's tale, scatter chicken bones, listen to Bob who heard it from Sam who heard that somebody they heard of had a fire... More controversy than what quantity of bear spray you should pack in the bush. Cut and dried. Easy apps, good information in Calder etc.

Obviously, the only correct answer is to use only 4/0 cable, for everything. Everything, then there can be no problems.
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Old 08-24-2015, 07:17 AM   #28
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Samr reasoning holds for a refit.

Buy a spool of #10 and most everything will be happy

Little downside in cost if you buy a big volume , same terminal ends for everything and with a set of stick on numbers from the Alarm folks , its easy to keep track, and create a schematic.

Only downside is #10 might weigh a bit more than #22 for a light.
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Old 08-24-2015, 02:11 PM   #29
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What's the old saying? "The nice thing about banging your head against a wall is that it feels so good when you stop!"

Quote:
I asked if the connectors between batteries could remain at 2/0 since the current between the individual batteries would be considerably less than that of the mail cables to the inverter charger.
Not so, current, which is measured in amperes, will be the same all across all the battery-related cables.

Quote:
But because my house bank will never see more than 220 amps and 99.999% of the time less than 20 amps, I used a #1 jumper that I had on hand. It works, and it is safe.
It is "safe" only if the battery bank is fused correctly to protect the #1. No big sustained surge items in your system? No inverter?
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Old 08-24-2015, 02:39 PM   #30
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Who here puts circuit protection on their jumpers between 6 V batteries?


yep...that wall is hard.....
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Old 08-24-2015, 03:27 PM   #31
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...The reason for 4/0 is because of the length of the cable run to the inverter charger and the associated voltage drop when under large loading. Since the current cable size is 2/0, I asked if the connectors between batteries could remain at 2/0 since the current between the individual batteries would be considerably less than that of the mail cables to the inverter charger. He indicated that while that could be done, he urged best practice would be to switch everything over to 4/0 all the way to the inverter charger...
Jim: We went 4/0 from the negative and positive of the battery bank to the inverter as per the manufacturer. I would have had a difficult time with the battery posts if I had done all the interconnecting with 4/0 because of the lug thickness. Check your post type and height. After 7 years with a 2800 watt invertor, the 2/0 interconnecting cables has worked with no issues.

side note: Our T-105's had ELPT (embedded low profile) posts. If our batteries had the EHPT (embedded high profile) posts, I would have been OK.
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Old 08-24-2015, 08:24 PM   #32
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OK....how do YOU base what wire size to use on a run?
Use the tables to determine a minimum wire size. Use a voltage drop calculator to see if you need to go larger, not to try to get away with smaller.
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Old 08-24-2015, 08:40 PM   #33
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Use the tables to determine a minimum wire size. Use a voltage drop calculator to see if you need to go larger, not to try to get away with smaller.
Right...so we all use the same tables...not sure what your point was to Kevin.
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Old 08-25-2015, 11:49 AM   #34
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What's the old saying? "The nice thing about banging your head against a wall is that it feels so good when you stop!"

Not so, current, which is measured in amperes, will be the same all across all the battery-related cables.

Clearly my electrician agrees with you!

Larry I'm not sure what posts I have. Probably the low ones I think. I guess I'll cross that bridge when I get to it!

For now I have the 2/0 cabling, but we need to do the load tests to see what the voltage drop is with higher inverter loads. I've only run the microwave occasionally and for a maximum of 3 minutes at a time. It's a 1000 watt model I believe so we haven't gone to the full potential of the inverter. The cables remain cool with the full charger load.


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Old 08-25-2015, 12:12 PM   #35
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Guys this is not really worth arguing to me.

No, I generally would not choose to use a smaller size inter cell jumper than my load cables.

I reserve the right to do so, simply because from a technical standpoint I can.

I am an old man and have spent a lifetime making a living thinking about among other things wire size and battery banks so I'm not too worried about my decisions in this area.

For the laymen out there... Use a wire size table. That way you will always get the right size cable for the job.
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Old 08-26-2015, 06:47 AM   #36
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To keep the heat down on those terminals , you might consider using copper nuts ,

as their ampacity is far better than SS.

Harder to find tho,,,,
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