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Old 22-07-2018, 14:47   #76
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Re: Sizing Main Battery Cables

Quote:
Originally Posted by rgleason View Post
Maine Sail,

Can a person using a DC Clamp/Volt meter capture these values?

For a Yanmar 3YM30 starter (64amp, 400cca) (While searching I found a forum email from you with these values, after your inquiry to Yanmar). Should I use:
  1. 200 amp fuse + awg 1 (existing wires) 12 feet full length.
  2. 225 amp fuse + awg 1/0 12 feet
  3. 250 amp fuse + awg 2/0 12 feet

For any battery than can be called on to start a motor I recommend a 250A fuse as a minimum. A 200A can work for many, many starts, I've experimented with one on my own boat, but it also may eventually nuisance trip if long cranking is required such as a fuel bleeding event. When possible I like to see a fuse rated at about 55% - 70% of in-rush. At this ratio I have never seen a nuisance trip.



Anyone can measure the in-rush or peak low/high voltage with the correct instruments such as a Fluke 376 (in-rush) or a Fluke 289 (peak voltages) a Midtronics analyzer (in-rush, average cranking load etc.), an oscilloscope and some other good quality tools...



It's not going to be very accurate with most cheap instruments, even cheap clamp meters that claim in-rush. A typical 1kW starter can draw about 370A for in-rush and about 100A continuous with ZERO LOAD and decent voltage... Add cranking an engine to it and the load is higher because we have moved from no load to loaded..


The YM starter has a "no load" rating of 90A at 11 volts. No load means spinning in free air.


It has a "loaded" spec (cranking an actual motor) of 250A at 8.4V. If you have a big bank and terminal voltage does not drop that much that 250A loaded rating can easily go higher..


Yanmar also specs a maximum allowable wiring voltage drop to the starter of 0.2V @ 100A (odd way to rate it). For 1AWG wire this would mean a max total circuit length, using 1AWG, of 8'..
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Old 22-07-2018, 15:14   #77
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Re: Sizing Main Battery Cables

Rod, Thank you! That resolves one of my problems. It appears that AWG #1 is too low just from calculation (with the right 90a starter amperage and 370a inrush) without a load, and that from your experience it is best to use at least a 250a fuses.


Your video Voltage Transients in A Marine Battery System
is hugely helpful to just understand the issues with large loads.
If I understood correctly the starter being used is for a Westerbeke 30hp motor, so it is a comparable starter to a 3YM30 engine.


I had not known about voltage transients and the necessary wiring considerations to protect instruments.
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Old 22-07-2018, 16:00   #78
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Re: Sizing Main Battery Cables

Quote:
Originally Posted by rgleason View Post
Rod, Thank you! That resolves one of my problems. It appears that AWG #1 is too low just from calculation (with the right 90a starter amperage and 370a inrush) without a load, and that from your experience it is best to use at least a 250a fuses.


Your video Voltage Transients in A Marine Battery System
is hugely helpful to just understand the issues with large loads.
If I understood correctly the starter being used is for a Westerbeke 30hp motor, so it is a comparable starter to a 3YM30 engine.


I had not known about voltage transients and the necessary wiring considerations to protect instruments.

90A is not the starter amperage it is the NO LOAD amperage rating. Meaning if you ran it on a bench not connected to a motor at 11V it would spin and pull 90A just top spin the motor into free air.. When you connect it to your engine, and the voltage of the battery sags to 8.4V, it should not pull more than 370A unless your starter terminal voltage is higher. In that case it could easily exceed 400A for short duration's.
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Old 22-07-2018, 18:02   #79
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Re: Sizing Main Battery Cables

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Originally Posted by rgleason View Post
Changes:
  1. Moved the 24hr Battery Fuse Panel AWG 6 to direct to Battery Positive + Post (less than 7" away)
  2. Moved the SW#1 AWG 1/0 to be direct to Battery 225a (eliminating two connections).
  3. Moved the Alternator AWG 1/0 to be direct to Battery 225a (eliminating two connections).
Is the Emergency Battery switch still meaningful?
There should not be more than one positive and one negative outgoing wire on a battery or battery bank. Use a bus.

Your emergency switch is not necessary and as with any connection it contributes to voltage drop.
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Old 22-07-2018, 18:11   #80
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Re: Sizing Main Battery Cables

Using Blue Seas Circuit Wizard
12v, 370 amp, 12', 3% voltage drop, variable load, engine room, terminated on fuse.
I get 4/0 wire and wire capacity of 378 amps.
This seems way too big. What am I doing wrong?

#1 works ok, engine starts right away.


Can I use an old ZapStop (I currently have on my Alternator) between DC Panle +/- to suppress transients? Would it work? Isn't ZapStop also a diode?... I saw the "...Sterling APD is not just limited to clamping transients from an alternator load dump it can also be placed across a DC electronics circuit or across the DC Panels B+ & B- feeders for added insurance," https://marinehowto.com/voltage-tran...rical-systems/
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Old 22-07-2018, 18:36   #81
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Re: Sizing Main Battery Cables

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Originally Posted by mitiempo View Post
There should not be more than one positive and one negative outgoing wire on a battery or battery bank. Use a bus.
Your emergency switch is not necessary and as with any connection it contributes to voltage drop.

Thank you for your thought and response.


Yes I understand that standard. Here is a wiring diagram with the main pos bus. This is a small boat with little room for wiring. See Existing

I am going use Trojan T105 batteries with EUT connections, with an MRBF fuse holder Blue Seas dual fuse holder 2151 or single 5191 turned on its side attached to the post to save space. It is kind of hard to see the drawing.

The 24hr Battery Fuse Panel is attached direct to the positive post with a #6 wire within 7", just as the many small + sensor and power leads would have been attached, with exactly the same number of connections, but consolidated in a single fuse panel.

The cables from the 1both2 switch and the alternator would be attached on the load side of the main battery fuse (not battery side) to reduce connections.

As far as the rest of the main + busway (Charger and ACR Combiner) I think those would be handled by a MRBF 5196.

John had suggested the emergency switch as good to have so I had shown it in earlier diagrams.
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Old 22-07-2018, 19:47   #82
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Re: Sizing Main Battery Cables

The emergency switch is good to have so you can take power completely away from the starter in case of a serious fault, like the starter not disengaging.
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Old 22-07-2018, 21:16   #83
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Re: Sizing Main Battery Cables

Thanks Terra Nova for the explanation for the switch.

From the Yanmar Manual pages 183, 184 through 188
Page 184, 12'=3.65m so 50mm(sq) is needed.
Page 185, 6'=1.8m so 20mm(sq) is needed.
Page 185, 12'=3.65m (if full length is intended), so 40mm(sq)

Looks to me like AWG 1 = 42mm(sq) will work for comply with pg185,
However complying with pg 184 AWG 1/0=53mm(sq) is needed.

From American Wire Gauges AWG sizes and cross sections
1 42mm(sq)
1/0 53mm(sq)
2/0 67mm(sq)
3/0 85mm(sq)
4/0 107mm(sq)

When I look at page 186 Chart 12.3.2
1. I know the engine starts at under 1000 rpm, say 800 rpm
2. On the torque curve 800 rpm is about 200amps
3. On the speed curve 1500rmp is about 200amps
4. On the volt curve 8.4v is about 250amps where the specs say current is 250 and rmp is 1000.

Why wouldn't a 200 amp or 250 amp fuse work?
AWG 1/0, would be 200amp or 225amp fuse
AWG 2/0, would be 250 amp fuse
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Old 22-07-2018, 23:18   #84
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Re: Sizing Main Battery Cables

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Originally Posted by Terra Nova View Post
The emergency switch is good to have so you can take power completely away from the starter in case of a serious fault, like the starter not disengaging.
You can do that just as well with the main switch.

My preference is a simple on/off for start and another for house.
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Old 22-07-2018, 23:25   #85
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Re: Sizing Main Battery Cables

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Originally Posted by rgleason View Post
Thank you for your thought and response.


This is a small boat with little room for wiring.
Lots of room for a 6" bus. It is common sense to keep battery wiring to a minimum and simplifies battery maintenance as well.

First thing I look at on a battery bank is the number of wires on the bank. More than 2 load carrying wires is sloppy.

Positive post to bus. MRBF fuses on the bus for individual loads. This way a blown fuse does not kill everything unless it is the main fuse.
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Old 23-07-2018, 08:38   #86
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Re: Sizing Main Battery Cables

Use 1/0 or 2/0 for all of your heavy load circuits. You should size these wire runs for a worst case scenario. A starter going bad, an inverter shorting, etc. Often battery cables are undersized due to cost and are insufficient to properly carry loads causing cables to get hot. When calculating loads add at least 30% safety factor for catastrophic failure. Once past the breakers or fuses normal sizes can be run since these circuits are protected.
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Old 23-07-2018, 09:37   #87
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Re: Sizing Main Battery Cables

One other issue is how you are charging your batteries.

If you have an inverted in the system you want to size the conductors properly.

Also how is the alternator wired? If you have a high output Balmar wired to the house battery bank ( directly) then you maybe able to use smaller cables. If you are using the starting circuit as the charge circuit be sure you are getting every amp. Bigger is better.
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Old 23-07-2018, 09:42   #88
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Re: Sizing Main Battery Cables

For future edification http://www.usawire-cable.com/pdfs/nec%20ampacities.pdf

There is a lot more to wire sizing than just grabbing a number. Temp, bundling, connections, etc to name a few.

Any wire will handle any current but the key is for how long and under what conditions. To much and the delta t is very short.
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Old 23-07-2018, 12:06   #89
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Switches: Emergency Switch, DCPanel and Starter, etc

Quote:
Originally Posted by mitiempo View Post
You can do that just as well with the main switch.
My preference is a simple on/off for start and another for house.
I think we have that ability with the proposed wiring:
1. DC Panel has its own switch and main Circuit Breaker.
2. DC Panel and Starter are on the "C" of the 1both3 switch and can be disconnected from any battery (off) or use House or Reserve battery sources.
3. Alternator has a safety disconnect switch as shown.
4. Charger does not have a dedicated switch on the dc side, but does have internal fuses, is also fused at the main positive busbar, and can also be shut off at the new 120v AC panel using the 15a Charger circuit breaker.
5. Battery 24hr Fused Panel has no switch and is wired direct to the positive battery post. It is the only thing other than the batteries that is not easily switched off. However the fuses can be removed.

Not including the Emergency Switch will make connections more direct with less voltage drop, which is good. The cons are that disconnecting the House batteries might require unbolting the terminal wires, and if there is some electrical problem that is not as quick or as safe. I currently have no emergency switch, and have not missed one, but that is no example to follow necessarily.

On the other hand, everything except the batteries and the Battery 24hr Fused Panel can be easily switched off. I am torn about whether to include the emergency switch or not, as I don't understand all the forces at work. Could the battery run away somehow and would an Emergency Switch help somehow?
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Old 23-07-2018, 13:01   #90
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Size conductors properly

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Originally Posted by CampDavid View Post
One other issue is how you are charging your batteries. If you have an inverted in the system you want to size the conductors properly. Also how is the alternator wired? If you have a high output Balmar wired to the house battery bank ( directly) then you maybe able to use smaller cables. If you are using the starting circuit as the charge circuit be sure you are getting every amp. Bigger is better.

CampDavid see the most current wiring diagram

  1. Charger -40a Stirling wired to the MRBF 5196 Positive Busbar + 80amp fuse. Wiring diagram shows AWG #6 and length of circuits.
  2. Currently the Alternator jumps over to the starter with a short 8" small cable and it uses the starter cable, clever, but that will be changed.
  3. Alternator -Currently Balmar 90-65, but will be changed to Balmar 60-120 or similar. Will be wired direct to main House Battery Fuse (250a to 300a). Alternatively direct to MRBF 5196 Positive Busbar (but using the main battery fuse 250a-300a). -On second thought maybe we do need a 150a fuse on the alternator at the positive busbar, my head is spinning after focus on the starter and learning about voltage transients and sizing from MaineSail. What a help that was!
  4. Do I need a fuse on the Alternator if the cable is sized conservatively?
  5. All the negative cables go to the shunt near the house battery bank rather than the engine ground to try to suppress voltage transients from the starter.
  6. I was thinking of using the old ZapStop that is on my Alternator now, to reduce voltage transients at the DC Panel. I think it is a diode and it might work (after I rewire the alternator).
  7. Solar - The other source is going to be Solar PV about 280-300 watts, wired through controllers to the Battery 24hr Fused Panel which is wired direct to the positive house battery post bypassing the main battery fuse. This panel also has all the voltage sensor fuses for the Smartgauge, Link, ACR Combiner, so it has to have no voltage drop from the battery.
Any further thoughts would be appreciated.
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