Sizing Main Battery Cables

[rgleason]

Mitiempo:

"I would use a 200 amp fuse for this alt.
You do not want to risk a nuisance blow of this fuse as it will almost guarantee the diodes in the alt will be destroyed."

I can change it from 175a in the next iteration. Very good point about alt diodes.

Aka:
"don’t leave your buss bar exposed where an errant metal tool can find and any ground at the same time."

This is a good point, since the only work area is the bulkhead in the port cockpit locker. I also want to be sure this does not get drenched by waves. Things are going to be hanging out a bit more than the current really simple unfused wiring.

Next post will be another prelim wiring diagram.

[rgleason]

Here is the next iteration: Would be interested in your thoughts again.

[mitiempo]

Why is your anchor light on the 24 hour panel?

The Smartgauge looks wrong to me - positive and negative should go directly to the house battery posts. B2+ to the start battery positive. Not to the 24 hour panel.

Combiner should not have a positive on the 24 hour panel. House+, start+, and a negative connection.

And I would forget the emergency switch - what do you think you need it for?

[rgleason]

Thanks for reviewing.

Originally Posted by mitiempo

Why is your anchor light on the 24 hour panel? -We are moored next to a channel & leave the photosensitive anchor light on and turn off the house DC panel at the main CB. Uses >.1amp and we have 14w PV for that light and recharge batts.
The Smartgauge looks wrong to me - positive and negative should go directly to the house battery posts. B2+ to the start battery positive. Not to the 24 hour panel. - Yes, I believe do, or the exact equivalent. FYI we use the start batt as "reserve". The Alt Output AO goes to House and the Regulator voltage sense/pwr wire goes to House +. The 24hr panel is directly wired to the House + with no fuse and is within 7" of the terminal. The number of connections and the fusing is exactly the same for the Smartgauge + wire to the House bank.
Combiner should not have a positive on the 24 hour panel. House+, start+, and a negative connection.
- Same deal. I did that to get rid of all those loose wires and fuses. I absolutely hate them. Everything in god's creation has to have "direct to pos + batt post" including loran and the kitchen sink. It's getting worse too. Are you telling me the combiner won't work?
And I would forget the emergency switch - what do you think you need it for?
- Well I just might. Still thinking about it. I've decided not to get a AFD version because of concern about the two voltage drops in the Regulator voltage sense/pwr wire, so just eliminating it is a definite possibility. What I might do is eliminate the Alt Service Switch and get a lockable Emergency Switch just to protect the alt diodes, in case someone unthinking turns it off while the engine is running. I am going to have to know that when servicing the Alt I have to disconnect the House Battery, because of the direct connection.

Does the 2/0 wire surprise you? Have I oversized it for this boat? I did use 2% voltage drop in the the BlueSeas circuit wizard and I also went up one size/30% for the major cables. I used the amperage multiplier as directed by the Charger manufacturer (120%) and 150% for the Alternator. I show the basis for the calcs in one of the images below.

[john61ct]

Some thing do absolutely require **direct bank post** connections.

Sensors is one category, and SmartGauge is in that, must be the same terminal/posts as charge and loads take off from.

Read Gibbo's instructions carefully, multiple times.

And look for Maine Sail's SG specific notes, e.g. https://www.sailnet.com/forums/showt...259089?page=21

[Stu Jackson]

Originally Posted by rgleason

Does the 2/0 wire surprise you? Have I oversized it for this boat? I did use 2% voltage drop in the the BlueSeas circuit wizard and I also went up one size/30% for the major cables. I used the amperage multiplier as directed by the Charger manufacturer (120%) and 150% for the Alternator. I show the basis for the calcs in one of the images below.

rg,




When spreadsheets first came out, engineers who worked for me jumped on them with both feet running.
Mistakes soared!!!
Why? 'Cuz they forgot the very first rule of doing calculations: do cross checks.
What I found was that they didn't check the results against expectations. Their answers in some cases were off by factors of three or more, simply because of "But the spreadsheet..."


Reason for this story: you are using a calculator, NOT mentioning every using tables or charts. Do you CROSS CHECK your calculator answer with a table or chart?

If not, you should.


[I'm not getting into the 2/0 sizing "thing" again, this is a separate objective pointer for you.]

[stormalong]

Wow, this topic sure has legs!

I use 2/0 to start a 50 HP engine with a ten foot round trip circuit.

I doubt you would need 2/0 for your engine.

Better for your peace of mind to go larger.

It is a one time purchase so little harm is done by spending a little more.

[mitiempo]

Smartgauge HAS to go to battery positive and negative. Otherwise it will not be accurate.

The emergency switch is totally redundant. Fuses are for emergencies and you will have them.

I understand anchor light.

Combiner only has 3 wires - positive to house bank (or bus), positive to start battery (or bus), and a small negative. I have no idea what the small combiner positive is going to the 24 hour panel but it is wrong.

Don't worry about Loran - it was shut down a few years ago.

[rgleason]

Here is a revised partial diagram. What is the difference between
1. 24hr Fused Panel - Smartgauge 3a fuse
2. Alternative location shown from the same connector as the 24hr fused panel

The exact same number of connections and both are directly connected to the +Post in the same way? Why isn't it the same?

[rgleason]

PS thanks for the link to Rob's Post 205


Mittiempo thanks for the wiring correction..

[mitiempo]

The Smartgauge is a unique product that HAS to be connected to the battery posts directly. It does not just measure voltage. It cannot see interference from other items wired to a busbar. Incorrect wiring to bus bars etc will seriously affect its performance.

See 1 and 2 here on page 2:

http://www.smartgauge.co.uk/pdfs/man...geman_r203.pdf

Wired the way your plan shows better to skip it - you're wasting your money.

Still shows the redundant emergency switch - what emergency?

I have wired many boats both for local cruising and offshore sailing. None has had an "emergency switch" as you show. It is not necessary.

Look at it with a "what is not needed for full function and safety" eye as opposed to "what can I add to it to improve it eye".

Simple is always better.

[rgleason]

I just noticed that the SI ACR Combiner #7610 is rated at 120a and I have shown 175a fuses at the busbars, is that incompatible?

I have sized 1/0 cable which is the max that the relay supports.

[mitiempo]

Originally Posted by rgleason

I just noticed that the SI ACR Combiner #7610 is rated at 120a and I have shown 175a fuses at the busbars, is that incompatible?

I have sized 1/0 cable which is the max that the relay supports.

ACR capacity is only your charging current. Your alternator (future) will be 120 amps. Your start battery if 100 AH will only accept 25 amps if it is a flooded battery. If it is AGM probable twice that for a very short time. 175 amp fuses are a lot larger than necessary. 120 or less - even 80 amps would be sufficient.

[Terra Nova]

The diagram shows only a portion of the circuits.

[rgleason]

Originally Posted by mitiempo

ACR capacity is only your charging current. Your alternator (future) will be 120 amps. Your start battery if 100 AH will only accept 25 amps if it is a flooded battery. If it is AGM probable twice that for a very short time. 175 amp fuses are a lot larger than necessary. 120 or less - even 80 amps would be sufficient.

Very helpful explanation Mitiempo, I had not focused on the start battery as governing the ACR Combiner in this iteration. I think I was using the alternator output, but actually it is the Reserve battery that governs. Earlier I had sized an 80a fuse and #4 wire. - Back to the drawing boards on the combining part of the system. Thanks again.

Two choices:
- Small Reserve Battery FLA, 70-100ah max, 25a acceptance.
- Enlarge the Reserve bank to equal the House (possible). FLA,225ah, 56a acceptance. Well within the ACR Combiner capacity.

I found a Wire and Fuse sizing chart in the SI-ACR Combiner 7610 Instructions
Charging Amps | Min.Wire | Fuse Rating
≤60 #6 75-90A
≤80 #4 100-125A
≤100 #2 150A
≤120 #1 175A
with caveat to use circuit wizard for distance, voltage drop, etc.
Thanks again.