alternator connection to primary battery bank

[mark_53]

1.  We do not recommend starting on Both.  First, our engines don't need it.  Second, if one bank is in poor health, the very last thing you want to do is to combine it with a healthy one.  If you move the AO off the switch, then the switch becomes only a USE switch.  In the old days, skippers who had the charging run through the switch tried to charge both banks vis the switch.  Those days should be over, by now. 

Agree, not a good idea to start on both IF you have a dead house battery.  That's when you first try to start on battery #2. If that doesn't work, nice to have the option of both.

[Stu Jackson]

1.  So you're needing to recharge only with batts?  Or w/ solar also? 

2.  I would start with a power budget and that will help define what alt you may want to upgrade to for cruising.  Then we can plan on that for the new cable -- otherwise you may have to re-do this again.

3.  A simple sketch of what you're doing and what you're replacing might help.  How many feet is the cable run?

1.  I think Ken meant "...only with the alternator..."

2.  A power budget is essentially meaningless in making this decision.  Over the course of the past decade and a half on this forum and almost 30 years with Catalina 34 Tech Notes, with a fridge, the daily use has been repeatedly measured at around 100 ah per day.  The only choice is how large an alternator one chooses to install.  It's that simple.  In addition, most of the regulars on this forum and Catalina 34 Universal engine owners have indicated that a 100A alternator is about the maximum that can be run with the existing 3/8" belts.  There is no need to reinvent the wheel here.  If your cruising uses a lot of motoring then a smaller alternator could work, but, again, regular contributors here have repeatedly pointed out that using a larger alternator can make sense, since it will work less.  Also, for most of us with ~400 ah house banks, we've found the acceptance of a 50% SOC house bank is around 50A-70A.  The size of your alternator along with the distance of the cable (BOTH + and -) determines the wire size.  Even the reuse of the OEM alternator could be helped by adding a ground wire from the alternator to the engine ground instead of using the case ground and the bracket as the ground.

As I mentioned earlier, whether or not you use the OEM alternator or install a new one, it makes a great deal of sense to install a larger wire for a future larger alternator now, rather than doing it again some time in the future.

3.  Ken, this seems to indicate, perhaps, your lack of familiarity with the layout of the Catalina 34.  99 44/100% of all Catalina 34s have their house bank in the same place, right forward of the galley sink.  Therefore, the only remaining variable is how the AO is run from the alternator to the house bank.  Many have routed it from the alternator, a few feet aft, and then down below and forward under the engine bed to the water heater/galley sink and then to the house bank.  This is an easily measured distance, either on the brochure floor plan of the boat or physically on the boat.

So, you have a maximum of 100A, and in reality you'd only see 70A to 80A and that for only a short period of time.  The distance is known.   Use any wire sizing table and you're done.

Harry, many, many of us have come before you.  There is a ton of "Here's how I did my system" contributions in the tech wiki, many with great detail on wire routing and sizing.

Good luck, let us know if you need anything more specific.

[Jon W]

With the AO going to the house bank, the fuse is protecting the cables from the house bank. I have a 250 A. Lots of discussion between 250 or 300 A. I've attached a pdf of my schematic as well. Also have a write up in the Tec WIKI on the complete upgrade.

Forgot the attachment again. Added it now.

[KWKloeber]

With the AO going to the house bank, the fuse is protecting the cables from the house bank. I have a 250 A. Lots of discussion between 250 or 300 A. I've attached a pdf of my schematic as well. Also have a write up in the Tec WIKI on the complete upgrade.

Forgot the attachment again. Added it now.

Hi jon,

I think he's asking about protecting an AO charge cable (ie, say w/ 60 amp fuse) not the starter cable (250 amp.)  Maybe I'm misunderstanding what's he's proposing (cuz I'm a visual/schematic, instead of description  kinda guy.)

ken

[J_Sail]

Ken,
You and Jon are both right. In Jon's case he used AWG 1 cable for his alternator output. That allowed him to safely share a single 250A fuse for both the starter cable and the alternator output (separate wires but a shared fuse connecting them to the battery).

In the case where one uses something lighter than AWG 1, the max fuse safely allowed for the alternator output wire would be smaller than the min size needed for the starter wire to avoid nuisance blows. Thus separate fuses are required. In that case, you can size the alternator wire's fuse anywhere between the max output of the alternator and the ampacity of the wire used. 

As to the appropriate wire size, that's been debated endlessly elsewhere, but the gist of it is that, if the alternator is internally regulated it cannot compensate for the voltage drop across the wire between it and the battery (both the positive wire and the ground path). A drop of even a couple tenths of a volt will significantly lengthen the time to fully recharge the battery. If you put the boat on a shore power charger once a week then that's not an issue. If, on the other hand, you sit on a mooring for extended periods of time with only brief motoring periods, you could risk chronic undercharging of the batteries, with a resultant major reduction in life expectancy. I recommend going with a bare min of at least AWG 4 for all cases (heavier better) and beefing it up to AWG 1 for the latter case (mooring with little motor use and no shore charger).  Given your alternator's low output ampacity, voltage drop is not as big a deal, but wire is not that expensive. 

[Jon W]

Paraphrasing info in my upgrade thread if the AO is connected to the house bank - The alternator is current limited at it's rating. The AO cable should be sized for that load so wouldn't need a fuse at the alternator end. The source it needs protection from is the house bank. If for some reason the cable fell off the AO terminal and contacted the engine it would cause a short circuit. The battery bank would try to feed the short and burn up the cable.

[Stu Jackson]

I think he's asking about protecting an AO charge cable (ie, say w/ 60 amp fuse) not the starter cable (250 amp.)  .............................

60A fuse on a #2, #1 or #0 cable?  Hardly.

All 200A per Blue Sea tables (included link in Elec 101)

[KWKloeber]

As J. posted, if it was a much lighter cable. Obviously not if you got a monster. Common sense.

[Stu Jackson]

As J. posted, if it was a much lighter cable. Obviously not if you got a monster. Common sense.

Our task here is to help Harry size his system:  equipment and wiring.

Your "common sense" POV must be supported by facts.

"Lighter cable?"  "Monster?"  What does this mean?

A #4 AWG wire fuse should be 150A.

The larger wires I mentioned earlier are all documented to have a 200A fuse.

Wires larger than #0 are simply not required by the load.  If they are, then a #2/0 wire (the next size larger than a #0 wire) would require a 300A fuse.  But I know of no installation in the range we are dealing with here that would require that size wire.  NONE.

I am temped to ask: "What the heck are you talking about? "

So, I will.

Please, please, please:  Stop obfuscating.

Your 60A fuse suggestion for the AO is simply wrong and way off base.

The Blue Sea tables and any other reputable fuse sizing charts are clear.

The concept is to help Harry, with scientific facts, well proven and documented.

And Jon's right, the fuse belongs at the battery end, NOT at the alternator.

[KWKloeber]

As I said, referred to J's post

In the case where one uses something lighter than AWG 1, the max fuse safely allowed for the alternator output wire would be smaller than the min size needed for the starter wire to avoid nuisance blows. Thus separate fuses are required. In that case, you can size the alternator wire's fuse anywhere between the max output of the alternator and the ampacity of the wire used. AS IN "60" for example (ed. comment)

chill out fercrissake you're going to have a effin coronary if you're not careful. This is a friendly meeting place. 
~~~Be happy, don't worry ~~~

YES it belongs at the btty end (nevah stated otherwise.)

If there's no future wire upgrade built in (which has not yet been predetermined by the owner), and if one is externally sensed, one doesn't necessarily need a monster cable.  Common sense says if a monster is used one might use a larger fuse.  However, on any conductor that's just a charge wire and not a starter cable, there's no point fusing monsterously above the max load (eg, AO current).

ie, if a 4/0 cable is run to power an "X" in order to absolutely minimize V loss, but carries 100 amps regularly, fuse is maybe 150, not 445 amps (for 4/0 awg.)    If a cable has dual purposes (say AO and starting), then it has to be fused for max load (ie, starting, say 250.)

kk

[KWKloeber]

Harry,

Can I clarify my reply TO YOU right below, since it seemed to cause some confusion.....?

Ken, In response to your earlier question..I currently am tied up and shore charging each evening..but plan on more extensive cruising (1-2 weeks) in the future
Harry

Harry so as Stu alludes to, what will your recharge needs be then, so you don't have to re-do wiring again.  When you say 2-week cruise, that means 2- weeks away from a charger?  So you're needing to recharge only with batts?  Or w/ solar also?  I would start with a power budget and that will help define what alt you may want to upgrade to for cruising.  Then we can plan on that for the new cable -- otherwise you may have to re-do this again.

A simple sketch of what you're doing and what you're replacing might help.  How many feet is the cable run?

below not to meant be curt, harry -- simply brief....
1) I don't have a C34 - don't know the run length (I didn't measure it when I chartered) -- so I asked you.

2) There's sometimes a propensity to "over do", "just because", add "bells/whistles", because "they did it."  I like to know exactly what and why I'm doing something -- does it meet or exceed my needs (and budget.)  A wire upgrade is a one-time cost, but there's still no need to overspend for what I absolutely need.

3) I don't know whether you'll cruise for 2 weeks, relying on the engine to recharge.  "Cruising" isn't well-defined -- could be "transient-ing" and @ a different slip every night ........ or on a hook for 2 weeks.  BIG difference in recharging/alt needs.  So a budget will tell how you'll spend your energy (negative cash flow) and how quickly you'll need to replenish the batts (checking account,) because recharging is in chunks (like a paycheck, not a constant positive cash flow offsetting each purchase.) 

4) An ulterior motive is that everyone *should* know more about their vessels and systems (especially electrical.)  You seemed as interested in learning about alts, cabling, as you were to "just give me an answer."   Looking at all of one's electrical uses, recharging, etc. is a a way to learn and understand more about everything 12v.  It can open eyes about usage (waste?) where one may not otherwise realize it -- e.g., should I buy all LEDs?  Not if I daysail and am on a charger every night, but maybe so if i will be on a hook for 2 weeks.  Maybe one never uses the fridge -- I know several "purist" sailors who don't.  I'm a "I like to prove it to myself" guy, rather than take things on their face --- it *helps* keeps my brain working.  If you're not so inclined, then that exercise may not be applicable.  To each his/her own.

5) I believe it's NEVER a waste to revisit something, yes something may be tried and true, not changed for 5 years, but I yahnevah know what tidbit I might pick up that could get one out of a jam in an emergency or possibly what lightbulb turns on upstairs when I work thru things myself.  Quoting a very knowledgeable forum member who has posted similar recommendations herein more than 25 different times, as recently as last month, it's just math and "An "energy budget" is the first place to start," and I thought possibly, per reasons in 1,2,3,4 above, that approach might also be useful to you (if you have the time.)  To each his/her own.

Hope that helps yah some, Harry!

Ken

[Stu Jackson]

It appears that the interpretation of 60A for the "...anywhere between the max output of the alternator and the ampacity of the wire used..." from Jon's post caused the confusion.  Sorry about that.

In any event, it seems to be incorrect, since the max output of the alternator may be less than the fuse required by the wire size.  Fuses to protect the wire must be sized for the wire size, not the load (amperage).  The size of the wire is determined by the amperage (load) and the length.

For example:  A #4 wire is capable of handling 55 A for a 25 foot cable run (which is about what the length is on our boats).  However, #4 wire requires a 150A fuse for protection, not a 60A sized "just" for the AO.

Regarding the "All Important Energy Budget", please note that it is has nothing to do with sizing an alternator.  The Energy Budget is used to size the house bank.  Period.  The size of the alternator, or any charging source for that matter, is determined, generally, by the amount of time required for recharging.  The smaller the alternator or shorepower charger or solar array, the longer it takes to charge a bank.  There are also general rules for charging sources sizing based on bank sizes.  For example, a shorepower charging source should be between 10% and 25% of the banks ah size in amps.

[Jon W]

I think you meant Jeremy's post.

[Stu Jackson]

Yes, you're right, Jon, sorry.

[mark_53]

It appears that the interpretation of 60A for the "...anywhere between the max output of the alternator and the ampacity of the wire used..." from Jon's post caused the confusion.  Sorry about that.

In any event, it seems to be incorrect, since the max output of the alternator may be less than the fuse required by the wire size.  Fuses to protect the wire must be sized for the wire size, not the load (amperage).  The size of the wire is determined by the amperage (load) and the length.

For example:  A #4 wire is capable of handling 55 A for a 25 foot cable run (which is about what the length is on our boats).  However, #4 wire requires a 150A fuse for protection, not a 60A sized "just" for the AO.

Yea, but if there was a short, do you want 150amps going into your 55amp alternator?