Sizing Main Battery Cables

[Zil]

I don't know the amperes needed. I don't want to see smoke from melting wires. Get the fuses right.

[rgleason]

I'll try to measure the amps, both starting and turnover. The turnover amps will be difficult because the engine starts so easily, it is almost instantaneous.

[Terra Nova]

Leave the shutoff closed, so it won't start.

[john61ct]

Or just assume 200-250A surge.

Short-term loads are impossible to measure with inexpensive tools.

[Zil]

What Maine Sail said.

[rgleason]

Thanks for this link Fusing & Termination
Since there is such a voltage drop due to fuses and multiple connections, I am inclined to remove the Emergency Battery Switch and the Alternator Service Switch and any other fusing or busbar that is unnecessary. The existing system is very direct with no fusing. I would be interested in which fuses and busbars could be eliminated, as these will seem pretty exposed mounted on the bulkhead.Please see Small Boat Electrical


Loads using 200a
- Starter (John says use 200-250a surge)
- Starter (3YM30) 64amps, 400cca
- DC Panel (max) 25amps
- Pos(+) to Neg (-) posts: 12' total, both red & blk
Blue Sea Calculator
Starter is in engine room -checked
Volts:12
Amps: 200
Duration: 1 min.
Length: 12' (length for DC Panel is 16', but that is the lesser load)
Battery CCA: 450
Main Circuit
Wire: AWG 1
Wire Capacity: 208a
Min. Rating: 200a
Suggested Rating: 204a
Fuses: 200a ANL 5129 and Terminal 5189
This is for the Starter only

Loads using 250a
Starter is in engine room -checked
Volts:12
Amps: 250
Duration: 1 min.
Length: 12' (length for DC Panel is 16', but that is the lesser load)
Battery CCA: 450
Main Circuit
Wire: AWG 2/0
Wire Capacity: 280a
Min. Rating: 250a
Suggested Rating: 264a
Fuses: 250a ANL 5131 and Terminal 5189
This is for the Starter only


The starter circuit fuses will have to be 200 or 250a and I may have to run 2/0

[Zil]

Remember. Proper sized switches and bus bars and fuses and cables, do not have that much voltage drop.

[rgleason]

Zil, thanks, I think I will read MaineSail very carefully and then add up all the connections without changing configuration yet.

One infuriating thing about the current schematic is all the fuses hanging off the battery + again. I got ticked about that and made a Battery Panel which is now full. I would like to move all these fuses into a second fuse panel. Is there anything wrong with that? Would there be too much of a voltage drop for the combiner and alternator, if I were to run a #4 wire from the load side of the battery fuse?

Ok, I refined the values a little and it looks like 225a fuses would work with the existing cables, but if I have to replace the cables, I should go up to a bigger size.

Loads using 220a
- Starter (John says use 200-250a surge)
- Starter (3YM30) 64amps, 400cca
- DC Panel (max) 25amps
- Pos(+) to Neg (-) posts: 12' total, both red & blk
Blue Sea Calculator
Starter is in engine room -checked
Volts:12
Amps: 220
Duration: 5 minutes
Length: 12' (length for DC Panel is 16', but that is the lesser load)
Battery CCA: 400
Main Circuit
Wire: AWG 1
Wire Capacity: 242a
Min. Rating: 220a
Suggested Rating: 230a
Fuses: 225a ANL 5130 and Terminal 5188
This is for the Starter only, but we aren't using the DC Panel generally when starting the engine.

[Terra Nova]

You want something like this for the fuses.

[Stu Jackson]

Originally Posted by rgleason

Thanks for this link Fusing & Termination
Since there is such a voltage drop due to fuses and multiple connections, I am inclined to remove the Emergency Battery Switch and the Alternator Service Switch and any other fusing or busbar that is unnecessary. >>>>>>>>>>>>>>>>>>>>>>>>>>

Please don't do that. The emergency battery switch (if IIRC your diagram, I haven't revisited it in weeks) allows you to swap banks for house use. The alternator service switch is a great feature, beats removing the fuse every time you need to work on the alternator.


Maine Sail's point is simple: IN ADDITION to the wiring voltage drop, you MUST include a REASONABLE drop for connections. That's all: reasonable.


But going back to what I wrote to you two weeks ago, when you figure out your wire size, you will ALWAYS find that your selected wire size is never exact for your load and distance, so you end up using the next size up which has a range, which then means the % voltage drop is LESS than 3% and things are just fine. Just never try to cheap out by using the smallest wire you think you can "get away with."


That said, it is YOUR choice about the wire sizing to the starter. I agree your amp assumption / research is low based on Maine Sail's reality-based real world studies. I'd use his results. But you're right, it's a high amperage, nanosecond load. And hanging a 2/0 wire off anything on an engine is a challenge for adequate proper support. Also covered by Maine Sail on his site, at least for alternators.

[rgleason]

In the calculation below, the AWG 0.

[rgleason]

Thanks Stu and Terra Nova,
I guess I am going to have to make all new cables now, and will redo the schematic again to show the battery panel larger to collect all those damn fuses (even though the BatteryGauge, Link10, etc all want to be placed directly on the Battery + Post. I have the BlueSeas 6 circuit panel (which is good) and will have to add another.

How do you guys feel about using 1/0 rather than 2/0 for this project? Is 2/0 going to be overkill? Will I have trouble up by the 1both2 switch etc. and making turns in tight areas? I've worked with 1/0 and have simply soldered the connections, but this time I guess I'll need to find the proper FTZ crimp tool. This seems to be getting expensive.

[mitiempo]

Originally Posted by rgleason

Zil, thanks, I think I will read MaineSail very carefully and then add up all the connections without changing configuration yet.

One infuriating thing about the current schematic is all the fuses hanging off the battery + again. I got ticked about that and made a Battery Panel which is now full. I would like to move all these fuses into a second fuse panel. Is there anything wrong with that? Would there be too much of a voltage drop for the combiner and alternator, if I were to run a #4 wire from the load side of the battery fuse?

Ok, I refined the values a little and it looks like 225a fuses would work with the existing cables, but if I have to replace the cables, I should go up to a bigger size.

Loads using 220a
- Starter (John says use 200-250a surge)
- Starter (3YM30) 64amps, 400cca
- DC Panel (max) 25amps
- Pos(+) to Neg (-) posts: 12' total, both red & blk
Blue Sea Calculator
Starter is in engine room -checked
Volts:12
Amps: 220
Duration: 5 minutes
Length: 12' (length for DC Panel is 16', but that is the lesser load)
Battery CCA: 400
Main Circuit
Wire: AWG 1
Wire Capacity: 242a
Min. Rating: 220a
Suggested Rating: 230a
Fuses: 225a ANL 5130 and Terminal 5188
This is for the Starter only, but we aren't using the DC Panel generally when starting the engine.

Is the 12' one way or there and back? If one way my calculator states 3/0 for a 3% voltage drop - not including connection loss.

Use MRBF fuses, neater than ANL and same quality.

Any battery or battery bank should have only 2 outgoing wires - one + and one -. Use buses. The MRBF fuse holders can be on the bus.

The Link 10 doesn't need to be on the + battery post. A bus is fine. It is only for voltage sense. The shunt is on negative post, then to negative bus.

[Stu Jackson]

Originally Posted by rgleason

Thanks Stu and Terra Nova,
I guess I am going to have to make all new cables now, and will redo the schematic again to show the battery panel larger to collect all those damn fuses (even though the BatteryGauge, Link10, etc all want to be placed directly on the Battery + Post. I have the BlueSeas 6 circuit panel (which is good) and will have to add another.

How do you guys feel about using 1/0 rather than 2/0 for this project? Is 2/0 going to be overkill? Will I have trouble up by the 1both2 switch etc. and making turns in tight areas? I've worked with 1/0 and have simply soldered the connections, but this time I guess I'll need to find the proper FTZ crimp tool. This seems to be getting expensive.

rg,


They are not "damn fuses" they are safety devices. Maine Sail has written how to gang them up on bus bars and use one wire to the bank.


"How do you guys feel about using..." I don't "feel" one way or the other. I am an engineer. I size wire based on the requirements of the charts and tables for wire sizing and loads. The ONLY place I can think of where a decision based on experience, rather than sizing tables, comes in is for the starter, because that ONE single short duration load involves a DECISION based on reality. Again, Maine Sail has done the homework there for you already, rely on his experience. Personally, I can't justify 2/0 wiring anywhere on a boat of your size (and mine) simply because the loads are not that large. The "other" loads from the battery to the panel and the loads get you one wire size (i.e., that discussion we had about your 50A panel fuse and the fact that if everything on your panel was ON at once it wouldn't get near even 30A) while the HUGE 250A starter load requires a wire size bigger than my forearm is overkill. THAT is where you have to make the decision.


Your boat, your choice.


FWIW, my 32 year old boat has GASP!!! #4 wire from the bank to the 1-2-B to the starter. It's OEM. Has been working for those 32 years. I even had a spirited discussion about this with Maine Sail over on sbo.com a few years ago. If it was new, I'd use bigger wire. It isn't, it works, I didn't. When I installed my bigger alternator I sized the new AO to the house bank for the larger AO for the rated cold AO of 100A, even though the AO is never that much except for a tiny amount of time at startup due to battery charging and acceptance even with a 50% SOC on my 400 ah bank.

[mitiempo]

Originally Posted by Stu Jackson

FWIW, my 32 year old boat has GASP!!! #4 wire from the bank to the 1-2-B to the starter. It's OEM. Has been working for those 32 years. I even had a spirited discussion about this with Maine Sail over on sbo.com a few years ago. If it was new, I'd use bigger wire.

Stu

Catalina used to use 4 awg for main cables but over the years corrected this to much larger wire.

When I replaced my battery cables and the wire to the starter with larger wire my cranking time changed from 10 - 15 seconds to almost instantaneous. Motors do not like low voltage.

I use 1/0 or 2/0 for battery inter-connects and wiring to the switch and starter for both banks, never anything smaller. Virtually all boat builders do currently as well.