Critique my wiring diagram?

[mitiempo]

Originally Posted by 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.

Your 6 Trojans will easily start your Perkins. I know this because on several boats where I replaced all the battery wiring 4 Trojans had no trouble starting their diesels of a similar horsepower. Battery wiring should be of a good size on both starting and house banks as in an emergency the house might be needed to start the engine - eg dead start battery. Battery cabling typically is 2/0.

[CatNewBee]

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

There are dual use AGM spiral cell batteries, expensive, but can be deep cycled and provide enough CCA. You can use a deep cycle house bank (e. g. GEL) to cranc and start the engine without stressing it, simply because your house capacity is 4 times ore more of the start battery. A 60..90Ah start battery is enough for a small diesel on a sail boat, while you have 240..480Ah for the house.

The problem is, you stay at anchor for a week, the house battery is depleted and then you want to charge it. The power is not there to cranc and you cannot push the boot downhill to start the engine like a car.

[RUSTYNAIL]

mitempo....The second wire I am talking about, is the small wire from the accessory terminal on the key switch. That terminal energizes the gauges, alarm buzzer, and one wire activates the alternator's voltage regulator, and on most panels, is the wire that has an in series resistor and warning light that comes on when there is no positive output from the alternator, stronger than the accessory B+ coming from the key switch input. When I disconnect the engine's battery switch, I want everything off to the engine. Not everyone may be concerned about this, and that's okay.

[Gene Neill]

Originally Posted by roland stockham

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

Respectfully, that is simply not true. For one thing, the boat came from the factory with a group 24 starting battery, which in 1979 would have held perhaps 70Ah?

For another, I have a 36Ah U1 (lawnmower type) battery which starts my 14HP engine again and again and again, over a period of several days, without any charging at all. I have not tested it to see the maximum times it will start the engine without difficulty, but I expect that number to be at least 20. I'll make a video, if there is a wager involved.

Maine Sail did a test, which I cannot seem to find just now, on how much power was actually used to start his own engine. It was astonishing little, something like 1/10th of one Ah, and his engine is twice the size of mine.

[rgleason]

mitiempo wrote:

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%.

Agreed, Balmar often suggests it is best to connect the external regulator sensing wires (-) and (+) from the external regulator, directly or near to the battery being charged where the (B+) cable goes, for more accurate and better charging.


I also agree with Gene about starting power. My Yanmar 3ym30 starts instantly with (2) Trojan 6vdc T105's (215ah). It also starts very easily with a 10 year old 12vdc West Marine Gel Cell at about 80% capacity.

[Ahmet Erkan]

rgleason wrote (at post #52) :

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

Well said but it is possible to arrive at a design that does not have disadvantages.
My comments are also interleaved.


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.
---->It cannot happen if you remove the offending component. (ie: get rid of the 12BO switch)
---->Emergency (ie: fire) shutdown switch at both house bank and starter batteries.
---->Charge the start battery from the house bank with a DC/DC charger. (keep a spare DC/DC)
---->Charge and maintain the starter battery fully charged whether the engine is running or not.
---->Buy a jumper cable for emergencies if you must.

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.
---->External or internal regulator, needs to sense and limit the output current.
---->An alternator charging a large house bank must meet this requirement to be reliable.
---->Waiting until the alternator overheats is not good enough, although it is better than nothing.
---->What can we do? Stop promoting products as "proper" just because the label contains the word “marine”.
---->Ask the salesman “Does this product actively limit the charging current at the rated Amps?”
---->Let us know if you find a product.
Cheers
Ahmet