Critique my wiring diagram?

[mitiempo]

Originally Posted by RUSTYNAIL

mitempo. I'd never argue with the Blue Seas team. Keeping the engine, alternator and start battery isolated, is important to me, even if it isn't the ideal way to charge. I have two Blue Seas digital voltmeters with alarms, so I never let my batteries get too low. That may save me from cycling the ACR. I live in the south, and that helps my solar system keep my house batteries topped off. My loyalty is to my start battery.

Wired properly, with the alternator and other charge sources going to the house bank, your start battery will be charged. When the house bank reaches 13 volts the ACR will close. The start battery needs a very small amount of current after a start. Besides it doesn't seem logical to pass a great deal of current through a start battery to charge the house bank.

[smac999]

I would swap the 1,2,all switch for a dual circuit on / off / combine switch. otherwise good.

Originally Posted by Gene Neill

I agree. That info will be added soon. For now, I don't know the lengths of the conductors, or even the exact batteries I'll be using.

Anyway, here's the latest incarnation. I added a reserve/starting battery (again, Ah approximate), and an on/off switch for the house bank. There will be a second bilge pump involved, but I think it will be wired from the breaker panel, so either bank can power it.

That's all I can think of right now. I spent the afternoon digging fence post holes, so my thinker isn't working very well right now. I need a shower and a cocktail very badly.

[Escape Plan]

Hey - how do you create the diagram? What software/site did you use?

[Gene Neill]

Microsoft Paint.

[RUSTYNAIL]

mitempo...It might not be true, but I see the start battery as a shock absorber for the small alternators with a single belt, when you start the engine. My ACR closes after maybe 30 seconds, and then everything is in parallel, so the current goes to the weakest batteries no matter where the alternator wire goes to. I am mainly concerned about a small 14 hp engine. I look for the weakest link in a system. I see great big bolts and cables on batteries and a tiny bolt and wire on an alternator on many poorly designed systems.

[Ahmet Erkan]

“My loyalty is to my start battery”. Me too, I think RUSTY NAIL has hit the nail in the head with this statement in post #45.
Here is my CRITIQUE of OP’s circuit design as he requested :
The original “Maine Sail” circuit prior to OP’s modifications also had these issues and the modified circuit did not resolve any of them.
1. The 12BO switch could be accidentally left in the BOTH position and the house loads can discharge both the start battery as well as the house bank. Unfortunately the skipper will find out when the dreaded click click click sound is heard upon trying to start the engine and a desperate look at the 12BO switch reveals it was accidentally left in the BOTH position.
2. If the engine started after a long cranking session and/or the start battery was half dead, the skipper may want to recharge and maybe equalize the starting battery as first priority right after the engine started. The circuit developed here will first recharge the discharged house battery (for a long time) before the voltage rises high enough for the Voltage Sensing Relay (ACR) to close and begin a concurrent recharge of the starting battery. Furthermore, even after the ACR closes, the start battery will be charging very slowly because the partially charged house bank will clamp the alternator output voltage until the house bank is fully charged.
3. Most alternators do not have built in overcurrent protection and the output current is limited by the resistance of the wiring. Furthermore, a starting battery normally discharges very little during normal cranking therefore even if the alternator is overloaded the energy is replenished in less than a minute and the thermal inertia in the alternator prevents any overheating.
Unfortunately a large capacity battery like a house bank and low resistance output wires (1/O wire is six times too large) may cause this alternator to deliver greater than the rated output current and thus have a hot and short life :-)

Just pointing out a few items that I consider unsolved issues, not suggesting any circuit changes. No need to jump into fixing a problem if the group does not think it is a problem.
Cheers
Ahmet

[rgleason]

There are many approaches to this system, some having more disadvantages than others. My comments are interleaved.

Ahmet Erkan wrote:

1. The 12BO switch left in the BOTH position and house loads can discharge both the start battery as well as the house bank.
--This can happen any way it it is wired. It hasn't happened to us yet.

2. The circuit here will first recharge the discharged house battery (for a long time) before the voltage rises high enough for the Voltage Sensing Relay (ACR) to close and begin a concurrent recharge of the starting battery. From another point "Furthermore, a starting battery normally discharges very little during normal cranking ...the energy is replenished in less than a minute.."
--Starting does not take much power generally, particularly with small engines. The house bank is more than adequate to start your engine. I consider the second battery a reserve battery, not a start battery. Thus the ACR just "maintains" that battery. I generally switch between off and one.

3. Most alternators do not have built in overcurrent protection and the output current is limited by the resistance of the wiring.
--I think it is important to charge safely and efficiently, treating your batteries to power within specs but more quickly than built in regulators, protecting the alternator, without running the engine more than necessary. Therefore it is reasonable to use a good external regulator properly programmed for your battery type with battery and alternator temperature sensors.

[mitiempo]

Originally Posted by rgleason

1. The 12BO switch left in the BOTH position and house loads can discharge both the start battery as well as the house bank.
--This can happen any way it it is wired. It hasn't happened to us yet.

Separate switches - one for start and one for house - solve this problem and are less confusing to anyone aboard.

[Gene Neill]

Originally Posted by rgleason

I consider the second battery a reserve battery, not a start battery. Thus the ACR just "maintains" that battery. I generally switch between off and one.

I have never owned an inboard-powered boat before, nor have I ever lived aboard any boat. But that is exactly the way I envision it. House bank for everything including starting, bank 2 for emergencies.

An upgraded, regulated alternator is in the plans.

[Gene Neill]

The panel is taking shape. Just had to share.

[roland stockham]

Originally Posted by Gene Neill

I have never owned an inboard-powered boat before, nor have I ever lived aboard any boat. But that is exactly the way I envision it. House bank for everything including starting, bank 2 for emergencies.

An upgraded, regulated alternator is in the plans.

This shows a fundamental (and probably common) misunderstanding of the way a start battery works.

The house bank should be deep cycle, it is designed to discharge at a low to moderate current over a long period and cycle down to between 60% and 40% DoD on a daily basis. Voltage will be nominally 12v but may drop to as low as 10.75v on occasions.
The start battery is not designed for cyclic use. When fully charged to 14.3v min it is designed to provide a short period of heavy discharge without dropping the voltage excessively.

A typical small diesel start battery has a rated cold cranking amps of 350-650amps and a capacity of 85-150a/hr. A typical house bank does not have a CCA rating but will have a 10 or 20hr discharge rating of 3-400am/hr. However its max discharge rating will normally only be around 60a.

Yes if the house bank is big enough and not to discharged it will start the engine but you are putting a stress on it that it is not designed to take so risk poor starting and/or damage to the battery.

If 'bank 2' is for emergencies what is it? a start batt or a deep cycle? If it is a deep cycle it will have to be very large to give reasonable engine starting, probable at least 300a/hr even for a small engine and most of the time will be wasted weight and space. If it is a start batt you cannot use it in emergencies as a house bank or you will damage it (start batt should not be discharged more than about 90% DoD and should always be recharged immediatly after use).
So why not use batt 2 as the start battery, fit one designed for the job and it will work much better for the job it is designed for. Then fit a house bank designed for cycle use to provide power for the services. If you fit a good house bank it should provide 10yrs reliable service and have sufficient reserve to run the boat for 3-4days in an emergency.
What you are proposing is both bad design and a recipe for trouble

[mitiempo]

Originally Posted by roland stockham

This shows a fundamental (and probably common) misunderstanding of the way a start battery works.

The house bank should be deep cycle, it is designed to discharge at a low to moderate current over a long period and cycle down to between 60% and 40% DoD on a daily basis. Voltage will be nominally 12v but may drop to as low as 10.75v on occasions.
The start battery is not designed for cyclic use. When fully charged to 14.3v min it is designed to provide a short period of heavy discharge without dropping the voltage excessively.

A typical small diesel start battery has a rated cold cranking amps of 350-650amps and a capacity of 85-150a/hr. A typical house bank does not have a CCA rating but will have a 10 or 20hr discharge rating of 3-400am/hr. However its max discharge rating will normally only be around 60a.

Yes if the house bank is big enough and not to discharged it will start the engine but you are putting a stress on it that it is not designed to take so risk poor starting and/or damage to the battery.

If 'bank 2' is for emergencies what is it? a start batt or a deep cycle? If it is a deep cycle it will have to be very large to give reasonable engine starting, probable at least 300a/hr even for a small engine and most of the time will be wasted weight and space. If it is a start batt you cannot use it in emergencies as a house bank or you will damage it (start batt should not be discharged more than about 90% DoD and should always be recharged immediatly after use).
So why not use batt 2 as the start battery, fit one designed for the job and it will work much better for the job it is designed for. Then fit a house bank designed for cycle use to provide power for the services. If you fit a good house bank it should provide 10yrs reliable service and have sufficient reserve to run the boat for 3-4days in an emergency.
What you are proposing is both bad design and a recipe for trouble

Any 12 volt battery selected for the "reserve" battery will very probably be either a start battery or a quasi- deep cycle that is close to a start battery in design. There are very few small 12 volt batteries - group 24 or 27 - that are true deep cycle batteries. Any of these will easily start a small diesel.

A house bank of a reasonable size will have enough cumulative cranking amps to start a small diesel. Maybe not each individual battery but multiple batteries will not have a problem. Not sure which batteries the Gene is planning to use for the house bank but if 12 volt group 27 or 31 they could well be not much different from a start battery anyway - see above. If they are GC 6 volts in series they will be true deep cycle batteries but still should not have any issue starting the small diesel in a 27' Vega.

[RUSTYNAIL]

My last two cents on this subject is important to me. Sending the alternator output to a different set of batteries than the engine control and voltage regulator source, is just "not good marine practice ". if you choose to use the start bank or reserve to run the engine, and send the output to the house bank, you have two different positive sources going to the alternator. In a bad situation, like a hot alternator due to a high resistant short or electrical fire, you should only have to turn off one engine battery disconnect switch. I wouldn't change anything on the Beta engine. I had one, and loved it.

[RUSTYNAIL]

I have Trojan 6 volt batteries for my house bank, and I hope I never need to use them to start my engine, because I have an 85 hp Perkins. The the internal connections are typically designed for maybe six batteries in series, and lower current, for golf carts, not several hundred amps through 3/0 cable.

[mitiempo]

Originally Posted by RUSTYNAIL

My last two cents on this subject is important to me. Sending the alternator output to a different set of batteries than the engine control and voltage regulator source, is just "not good marine practice ". if you choose to use the start bank or reserve to run the engine, and send the output to the house bank, you have two different positive sources going to the alternator. In a bad situation, like a hot alternator due to a high resistant short or electrical fire, you should only have to turn off one engine battery disconnect switch. I wouldn't change anything on the Beta engine. I had one, and loved it.

The voltage regulator, on a standard alternator, measures through its output wire (B+). If using an external reg the sense wire should go to the charged bank of course - eg the house bank. There will never be 2 different 12 volt sources going to the alternator. It is turned by a belt and it wiring is exclusively to the house bank.

If you have not changed anything on your Beta engine the B+ wire goes to the starter, as any engine is when delivered. Whichever battery is used to start it will get the charge current wired this way.

It makes the most sense to send the charging current to the battery bank most in need - the house bank. If you have read much written by Mainesail he agrees 100%.