Alternator B+ To Starter Post Or Combine Post

Maine Sail · Apr 23, 2015

Stu Jackson said:
Nick,

Here's another place where MS says my #4 is too small.

http://forums.catalina.sailboatowners.com/showthread.php?t=170859

Stu

Stu,

There is a good reason builders are no longer using #4 and one of the major reasons is that it can't be adequately fuse protected to drive all the loads on today's boats. The other reason is voltage drop during high loads which are not good for such things as starter motors or windlasses. I routinely measure voltage drops on boats with 4GA wire in excess of 1.5V during starting and occasionally as high a 3V.. This is on top of the battery voltage sag that is also occurring. I replace a lot more failed starter motors on boats with small GA wire than I do on boats where the builders used larger GA wire during the same build vintage. If the wire is short enough 4GA can works but on many of these boats I see more than 20' of 4GA wire in the starting circuit especially when the battery switch is located in a DC panel..

The problem with most voltage drop calculations is they only include the wire and totally ignore terminations, fuses and switches. Wire voltage drop is only part of the equation the reality is what is the installed voltage drop.

Will 4GA start an engine? Sure, of course it will. Is it ideal and can you adequately fuse protect that engine with #4 and avoid nuisance trips? Barely, and to do this you'd really need to utilize the ABYC 150% of max ampacity allowance, which is really not ideal either and also have 105C 4GA wire. When you consider that much of the 4GA wire installed in the 70's & 80's was 75C wire, not 105C wire, that means a starter wire that originates in the engine bay could only use a 140A fuse max and this is already taking advantage of the 150% rule. At 100% of max ampacity this wire could be fused at no more than 94A if one were to "follow the standards". Of course, as I always say, any fuse, provided it avoids nuisance trips, is better than no fuse at all.

But hey it is not just me that "opines"..

Universal / Westerbeke BATTERY CABLE REQUIREMENTS (wire length round trip)

2GA = 8'
1GA = 10'
1/0 = 14'
2/0 = 18'
3/0 = 22'
4/0 = 28'

Charging Circuit & Voltage:

For charging circuits where remote voltage sensing is possible I still don't like to see more than 3% voltage drop. For boats with self sensed alternators 3% of 14.4V is 14.0V at the batteries. This is ideally too much drop, if you want any semblance of short term high current charge performance. Will a 3% drop work? Sure? Is it ideal for the way sailors like to charge? Not really.

Last Friday, Saturday and Sunday I was working on a Sabre with a factory Westerbeke alternator. It had 1.3V of drop at just 30A of charge output (.8V in the negative side alone). That means the alternator was at 14.4V and in absorption (limiting voltage) while the batteries were at 13.1V. In this scenario current can only go down because the alternator is now limiting the voltage. This owner had been through a bank of batteries every two years. He now has a .2V drop at 46A which is about the max his alt will produce. Is this "ideal", no, but it fits his budget and will get him significantly better battery life. It makes him happy and that is what matters..

The way we use batteries on sailboats means we want to get as much energy back into the batteries in the shortest time possible. The owner above is adamant about not running the engine more than 1 hour per day. This is why his batteries were dead in two years. If you are losing .4V (3%) then you will dig into your fast charging performance and the regulator will enter absorption mode before the batteries do. If you have a remote sensing regulator wired properly then I'd still suggest aiming for 3% max on the alt circuit for the best charging performance.

These are the types of performance differences I am talking about with voltage drop issues.

No direct battery voltage sensing and a .7V drop at 50A (not at all unusual as installed)

Points to Ponder:

In 1 hour of charging, at a .5C charge rate, the battery voltage never exceeded 14.3V.

At just 14.0V, measured at the battery terminal's, the charger began limiting voltage. When measured at the charger end, it was seeing 14.7V and it began holding the voltage steady. This is what forces current to decline.

Once the voltage is held steady current tapers off and charging speed reductions are happening.

Maximum bulk time was limited to 30 minutes at 50A, due to the voltage drop. This resulted in just 41.93 Ah's delivered to the battery in the 1 hour recharge period.

With Voltage Sensing:

Voltage sensed directly at the battery terminals and wires sized for minimal voltage drop. 1 Hour recharge at 50% of Ah capacity.

It looks a little different with good voltage sensing..

In 1 hour the charge source delivered 49.37 Ah's to the battery. This is an improvement of 7.44 Ah's in just a short 1 hour charge cycle. This equates to a percentage increase in charge performance of approx 17.7%, just by moving two small wires and essentially eliminating voltage drop in the charging circuit..

Bulk charge at 50A increased by 20 minutes to a full 50 minutes of bulk charging. This was a 100Ah battery charged at 50A for just 1 hour.

The battery actually attained the absorption voltage set point of 14.7V. This is healthier for the battery than stopping at 14.3V. It can help limit some of the effects of sulfation, even in a short 1 hour recharge. The effects of attaining your regulation voltage at the terminals, for a long enough duration, will have a direct impact on the longevity of the batteries.

In the previous test, with no voltage sensing, that battery would suffer performance issues considerably faster due to never even attaining the 14.7V target with daily 1 hour recharges.

It all boils down to what you are happy with. I like to see customers get their money's worth and I don't like to see short lived starter motors or battery banks when by making a few small tweaks we can certainly improve both situations.

Stu Jackson · Apr 23, 2015

Wire sizes 3

Maine Sail said:
Stu,

1. There is a good reason builders are no longer using #4 and one of the major reasons is that it can't be adequately fuse protected to drive all the loads on today's boats.

2. It all boils down to what you are happy with. I like to see customers get their money's worth and I don't like to see short lived starter motors or battery banks when by making a few small tweaks we can certainly improve both situations.

1. I agree. The "drive all the loads on today's boats" is the one point I am not sure of. Here's why: My point earlier was that my boat has been starting just fine with the #4 wire from the bank to the switch to the starter. Yes, I agree, there would be less voltage drop for the very short duration of this load, and that a higher voltage at the starter would be good for the starter. "Driving all the loads", however, isn't an issue for this wire, other than the starter, at all, because the only other thing the #4 wires "service" is the distribution panel. In all my years on my boat, I know the amp draw of every single component. Even if I turned ALL of my loads on at the same time, I would still be drawing way less than 30 amps, which is fine for the #4 from the bank to the DP. I simply am not going to be running my bilge pump, macerator pump, fridge, ap, all my lights and the shower sump pump at the same time.

So, I'm somewhat confused by the "loads on today's boats" which really aren't all that much different than they were 30 years ago, at least on my boat which had all those bells & whistles installed when it came from the factory. The #4 wire fusing of 150 or 125 would be too small for the starter.

2. I am a believer about battery sensing for the alternator. If you recall, you were the guru who made me see the light a few years ago. I even commented on it here on this forum: http://forums.catalina.sailboatowners.com/showthread.php?p=846989&highlight=battery sense

As a result, I am getting the right voltage AT the bank.

I couldn't agree more with you about seeing happy customers and boaters. It's not so much "what I like" but also what I've learned from you and your references to wire sizing and fuse sizing tables. That Blue Sea table is great and I've saved it as a PDF and refer to it all the time.

If I was rewiring my boat, I would use #2 from the banks to the switch to the starter. I have already rewired just about everything else.

For Nick, please, please, please, listen to Maine Sail, not just me. I'm just providing you with options for your consideration, since you did ask about what I would do re: wire sizing, and I explained why.

It's not only "Your boat, Your choice

," it's important to follow the rules, use the tables, and do the appropriate calculations.

Solstice · Apr 23, 2015

Just to be clear, my reference to 4 AWG is only for my 60 amp dumb Alt. Everything else is 2/0 on my boat. Not sure if that got lost in the thread, so just wanted to point that out....

Maine Sail · Apr 23, 2015

Stu Jackson said:
1. I agree. The "drive all the loads on today's boats" is the one point I am not sure of. Here's why: My point earlier was that my boat has been starting just fine with the #4 wire from the bank to the switch to the starter. Yes, I agree, there would be less voltage drop for the very short duration of this load, and that a higher voltage at the starter would be good for the starter. "Driving all the loads", however, isn't an issue for this wire, other than the starter, at all, because the only other thing the #4 wires "service" is the distribution panel. In all my years on my boat, I know the amp draw of every single component. Even if I turned ALL of my loads on at the same time, I would still be drawing way less than 30 amps, which is fine for the #4 from the bank to the DP. I simply am not going to be running my bilge pump, macerator pump, fridge, ap, all my lights and the shower sump pump at the same time. So, I'm somewhat confused by the "loads on today's boats" which really aren't all that much different than they were 30 years ago, at least on my boat which had all those bells & whistles installed when it came from the factory. The #4 wire fusing of 150 or 125 would be too small for the starter.

2. I am a believer about battery sensing for the alternator. If you recall, you were the guru who made me see the light a few years ago. I even commented on it here on this forum: http://forums.catalina.sailboatowners.com/showthread.php?p=846989&highlight=battery sense

As a result, I am getting the right voltage AT the bank.

I couldn't agree more with you about seeing happy customers and boaters. It's not so much "what I like" but also what I've learned from you and your references to wire sizing and fuse sizing tables. That Blue Sea table is great and I've saved it as a PDF and refer to it all the time.

If I was rewiring my boat, I would use #2 from the banks to the switch to the starter. I have already rewired just about everything else.

For Nick, please, please, please, listen to Maine Sail, not just me. I'm just providing you with options for your consideration, since you did ask about what I would do re: wire sizing, and I explained why.

It's not only "Your boat, Your choice ," it's important to follow the rules, use the tables, and do the appropriate calculations.

On today's boats was the key phrase in that sentence.

For example many inverters require 2/0 or 4/0 wire and tapping them into a house bank wired with 4GA.....

More and more of today's boats are coming from the factory with 2kW to 3kW inverters even in the sub 40' range. For your boat 4GA is working and has worked. I am not trying to suggest you make any changes...

It is not how I would wire a paying customers boat, nor how Westerbeke/Universal wants their engines wired nor how Catalina does it today but it does not mean you need to change...

Solstice · Apr 23, 2015

Solstice said:
Just to be clear, my reference to 4 AWG is only for my 60 amp dumb Alt. Everything else is 2/0 on my boat. Not sure if that got lost in the thread, so just wanted to point that out....

Oops, not so clear. I meant to say 2 AWG on my Alt. Sorry about that...

Stu Jackson · Apr 23, 2015

Wire size repeat

NICK1951 said:
Stu,

I probably misspoke, not the first time! The engine starts fine, however it needs 40 seconds of glow plug before starting. I have seen your posts on the glow plug solenoid and look forward to discussing this with you in the future. I agree, 4 awg works. I contend 1/0 has less voltage drop. Having said that I am not hung up on upgrading to 1/0. 4 awg will save me some money.

I like the start/ reserve concept, perhaps I am misguided. To add the start/ reserve I will need to add new wires, just figured I might as well replace all of them. The existing wire and lugs are not tinned or adhesive heat shrinked. The overriding concern in upgrading to 1/0 is the ability to fuse, properly. 1/0 allows me to fuse at 250 amps. I believe this will be appropriate on a starting circuit. 4 awg requires a much smaller fuse.

Bottom line, I want to provide over current protection. If the fuses blow, I will scratch my head and say I goofed.

As always, I appreciate your thoughts. I am curious do you have over current protection?

Nick

Nick,

I answered this is detail earlier, but somehow my post got "lost" - I know it was there because I edited it a few times, and now it's just gone.

Instead of trying to rewrite everything I did before, I agreed with what you said, and look forward to answering any questions you have about the solenoid. Lots of what I said was included in my reply to MS.

Stu Jackson · Apr 23, 2015

Wiring size 4

Maine Sail said:
On today's boats was the key phrase in that sentence. For example many inverters require 2/0 or 4/0 wire and tapping them into a house bank wired with 4GA.....More and more of today's boats are coming from the factory with 2kW to 3kW inverters even in the sub 40' range. For your boat 4GA is working and has worked. I am not trying to suggest you make any changes...

It is not how I would wire a paying customers boat, nor how Westerbeke/Universal wants their engines wired nor how Catalina does it today but it does not mean you need to change...

Understood and thanks. We DO have a 1500 watt inverter (a Freedom 15 I/C), and DO have 2/0 wiring from it to the house bank.

And, as I said, if I was rewiring my boat, I'd use #2 to replace the old #4.