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Old 04-17-2017, 03:46 PM   #1
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Battery switches / isolator

Hate to bother you folks again on this subject.

I've got twin Perkins with a group 31 deep cycle battery for each and the lower helm is equipped with battery switches (off, 1, both, 2) that purportedly will enable me to start either engine with either battery. Additionally, I have a house bank (currently 4 6v batteries) and the 12v house panel has a switch for two batteries (off, 1, both, 2).

Nothing seems obvious about how the boat is really wired; I cannot see how the two helm position switches are interconnected and it does not seem to make any difference to whether they start. It also does not seem to have hurt anything(!) by having both switches off; the alternators still work.

Since the boat was pulled last fall, the battery banks went totally flat and the 110v charger refused to charge anything. I've since found that one of the start batteries was probably faulty and was boiling. I disconnected it totally; the charger and the other two banks seem fine.

The Charles 20 amp, 2000SP, battery charger has separate outputs: Marine: 2000 SP Series Battery Chargers but apparently it cannot tolerate a failed battery. Yeah, it looks haywired: something to fix; pic.

It appears that the Perko diagram below is appropriate for the boat except that it does not show how to interconnect the start bats with the house bank which might be a nice thing to be able to do. I also do not have a stand-alone genset start batt.

I am reasonably certain that I do not have a battery isolator, thus it would seem that the charging circuit interconnections inherent in the engines' alternators would serve to flatten all batts. I presume that the Charles 110v charger isolates the batts.

It would seem that I need to figure out the wiring and interconnections and add a battery isolator. The Guest 2503 at $400 seems to be a reasonable, but expensive choice.

Comments? Enlightenment? Newby here; it should be obvious.
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Old 04-17-2017, 03:59 PM   #2
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While sounding more complex, this would be keep it "simple." A simple On -OFF Battery switch (like the Perko 9601) between the house and the engine grid and same with generator to engine grid.

Allows you to make any possible combination of connections except just House-Gen

maybe?


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Originally Posted by DHeckrotte View Post
It appears that the Perko diagram below is appropriate for the boat except that it does not show how to interconnect the start bats with the house bank which might be a nice thing to be able to do. I also do not have a stand-alone genset start batt.
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Old 04-17-2017, 04:20 PM   #3
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First you need to be 100% sure how the system is wired now.

Then, as mentioned, you can install simple on/off switches where needed to manually "jump" together any combination of batteries you wish.

I would not use a battery isolator. I'd use a combiner.
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Old 04-17-2017, 05:25 PM   #4
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As others have mentioned, you need to trace the wires and see what it is that you currently have.

Generally, I think that it is better for the alternator to go directly to the battery than to a 1/2/Both/Off switch, and it sounds as if that is the way yours is wired.

It doesn't sound as if your boat's wiring bears much resemblance to the diagram. So figure out what you have, then you can figure out what you want.
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Old 04-17-2017, 05:46 PM   #5
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The best advice I can give is:

KEEP IT SIMPLE SAILOR!!

One solid two or three Group 31 Dual Purpose batteries will easily start all three motors of the same buss bar. Then it is just a matter of house bank. Make it as big or as little as you need and drop both alternator wires to it and charge the start batteries with your favorite ACR or Duo Charger.

As for switches. There are lots of ways to do it. Lots of people use single on/off with a single on/off as a combiner. I did it a little differently and used two 1/2/Off/Both switches. One for the motor circuit and one for the house circuit.

It is very easy to design... easy to wire... easy to operate... easy to understand. Moreover, it has FAR fewer points of failure. And in your case, less stuff to buy.

Below is a snip on my design. The only thing different than what I ended up with is that I have yet to opt for a separate genset battery. I just reprogrammed my charger for when we are at anchor running the genset. Good luck!
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Old 04-18-2017, 07:35 AM   #6
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Remember any switch that can disconnect the running engine from the battery its charging MUST have a field disconnect built in..

These are the two small poles on the switches and the wiring to and from the alt will need to handle 10A at most.
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Old 04-18-2017, 08:27 AM   #7
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Quote:
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Remember any switch that can disconnect the running engine from the battery its charging MUST have a field disconnect built in..
With all due respect, not all battery switches have alt field disconnects, and few battery switches are wired with alt field disconnects.

While "things" happen, there is no logical reason to turn a battery switch to off with the engine(s) running. Also all popular battery switches are "make before break" which means when switching between 1-2- all the switch never disconnects.

While a nice feature to keep people out of trouble with their alternator, saying any switch with an off position MUST have an alt field disconnect is just not true or current practice. Just don't turn the switch to off with the engine(s) running, there is really no reason to.

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Old 04-18-2017, 09:28 AM   #8
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Another reason to connect alternators directly (however fused) to the house bank.
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Old 04-18-2017, 10:35 AM   #9
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Another reason to connect alternators directly (however fused) to the house bank.


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Old 04-18-2017, 10:50 AM   #10
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Quote:
Below is a snip on my design. The only thing different than what I ended up with is that I have yet to opt for a separate genset battery. I just reprogrammed my charger for when we are at anchor running the genset. Good luck!

A great battery diagram that makes sense ( to me ) thanks for sharing.

I see a lot of reference to " battery isolators - combiners etc " here. I would be skeptical of any diode based device as I think there would be a forward voltage drop. + / - 1 V maybe more, depending on the quality of the diodes, unless they are Schottky diodes which are quite expensive at alrge currents. Frank B.
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Old 04-18-2017, 12:10 PM   #11
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Isolators incorporate diodes and the associated voltage drop. If you have an alternator voltage regulator on that circuit, it may be able to be adjusted to compensate for that 0.7-1.0V drop.

Combiners do not use diodes so there's no voltage drop.

Here's a copy of my layout. Many of the components have been upgraded since this was drawn up years ago (new stbd alternator, charger, start battery and combiner), but the layout remains the same. The key concept here is that the alternator charges go directly to the batteries and can be shared by the combiner if one charge source is not available. Only the loads are controlled by the switches.
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Old 04-18-2017, 12:39 PM   #12
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"Just don't turn the switch to off with the engine(s) running, there is really no reason to"

True enough but "stuff happens" and even children visit ,

The cost difference between a switch that will save the alt and one that wont is very tiny.

We pay big bucks for insurance for other folks , a proper switch is such a tiny outlay and it is insurance for YOUR boat.

Plan B is a locking cover to keep helpers out of the system.
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Old 04-18-2017, 03:00 PM   #13
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Quote:
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"Just don't turn the switch to off with the engine(s) running, there is really no reason to"

True enough but "stuff happens" and even children visit ,

The cost difference between a switch that will save the alt and one that wont is very tiny.

We pay big bucks for insurance for other folks , a proper switch is such a tiny outlay and it is insurance for YOUR boat.

Plan B is a locking cover to keep helpers out of the system.
Even better insurance is to have the alternator go directly to the battery instead of a switch. That way it can't be accidentally disconnected. So many 1/2/B/O switches, at least on sailboats, are wired so that the position of the switch determines both the load as well as the charging. Not a good setup IMO.
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Old 04-19-2017, 06:35 AM   #14
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"Not a good setup IMO."

Not a problem at all IF the rotary switch includes a field disconnect.

The key is "do no harm".
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Old 04-20-2017, 04:34 PM   #15
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The KISS principle is alternators direct to batteries with an inline fuse.
Eliminates user errors.
I have a single start battery and two house batteries, two alternators, two 3 wire battery switches.
One alternator charges start battery, other house batteries.
I added a combining relay with a manual switch.
I think I set it up so relay only activates if starboard engine is has oil pressure and the manual switch is set to on. Or it might be when ignition is on.

An ACR is more pricey but automatic.

I was watching the port alternator barely charging start battery while starboard was heavily loaded charging house batteries. When I turn on the combining relay, port alternator amps output jumps up and starboard drops, so evens out the load on them both which I like. And honestly I could just leave the relay set to go on all the time, it still keeps separate start bat from house unless starboard engine ignition is on.

If start batt is dead, simple rotating the big 3 wire switches can select different batt combinations.
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Old 04-20-2017, 05:02 PM   #16
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Remember any switch that can disconnect the running engine from the battery its charging MUST have a field disconnect built in..
In all my years of working on boats I can count on my hands the number of times I have seen the AFD feature being utilized. Of those times where it was being utilized it was wired incorrectly in 98.5% of those situations.

The key word is alternator FIELD disconnect. This means it must interrupt the field (power from regulator to slip rings) & be inserted between the internal regulator and the brush.

Cutting the "excite" wire with a powered up alternator does not protect the alt from a load dump because once excited they self excite.. Only breaking the field (brush) or the B+ power wire to an external regulator will do this. It should be noted that cutting the ignition wire to most external regulators is not fast enough to save diodes and it must be either the field wire or the regulator B+. Most regulator manufacturers & their designers, would prefer the B+ to be cut over the Field wire.

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These are the two small poles on the switches and the wiring to and from the alt will need to handle 10A at most.
This will work fine provided you are breaking the field or B+ of an external regulator. Some internal regulators are very tough to tap into and break B+ but the brush wire can more easily be interrupted. Again nearly every AFD switch I have seen wired, to use AFD, has been wired incorrectly. If you've wired yours correctly this is great and you're in the top 1.5% !!

Best course of action, for charging performance, is to direct wire the alternator to the house bank and let charge management devices (ACR's, Combiners, Echo Chargers or DC to DC battery to battery chargers) take care of the start & windlass or thruster banks....
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Old 04-20-2017, 05:22 PM   #17
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Comments? Enlightenment? Newby here; it should be obvious.
On a boat of your size I would suggest you simplify. Four banks is major overkill on a sub 40' boat...

You're lugging around far too much "dead lead" that can be put to significantly better use when placed into a house bank and actually used "live lead" instead of sitting there at 99.5% + SOC all the time.

Simplify:

One Start Bank - For all three engines, including the gen set. Two Group 31's would be overkill here or keep one of the 4D's. Two G-31 deep cycles will usually exceed the cranking capability of a 4D and generally serve you better if you ever had a house bank failure than the 4D would.

One House Bank - Build this bank larger and make your lead usable not wasted as multiple starting batteries.


Create a Switch Configuration That Can:


*Allow Bank 1 to be used for both starting and house loads in an emergency

*Allow Bank 2 to be used for both starting and house loads in an emergency

*Allow full isolation of the bank not being used in an emergency

Starting a motor, even massive ones, barely uses 0.1% - 0. 5% of your start batteries capacity, so why lug that 99.5% + around, just waiting to use it , and then you never do?

This dead lead is put to far better use as live lead in the house bank.

Charging Sources to House -
With a twin engine set up feed all charging sources to house, with the exception of the smallest alternator, for the start battery. Place a VSR/ACR/Combiner between the banks and then both alternators contribute current to the charge bus where it is most needed. This yields optimal charging performance and gives a very simple system.
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Old 04-20-2017, 06:01 PM   #18
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Old 04-20-2017, 07:12 PM   #19
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Here is an example of a 2-Engine, 2-Switch, 2-Battery DC electrical layout as installed by the Wellcraft factory in my newest boat. It is a very basic, or what I originally thought was a 'primitive' electrical system. There are no battery isolators, and only switches to combine the two batteries. There are no dedicated 'House' batteries or 'engine start' batteries. I was about to re-engineer it with ACR's, remote switches etc. until I began to study it a bit. I have concluded it is almost brilliant in its simplicity, and I might not change a thing. KISS.

There are two battery selector switches (1-2-Both-Off) connected to two identical 4-D FLA batteries, #1 (PORT) and #2 (STBD).

There is a modern Mastervolt 3-Bank smart battery charger with connections from Bank #1 to battery #1 and from Bank #2 to battery #2.

The #1 (PORT) switch is connected to the #1 (PORT) starter/alternator and the 'helm' with electrical items connected like trim tabs, bilge pumps, livewell pump etc.

The #2 (STBD) switch is connected to the #2 (STBD) starter/alternator and the 'Cabin' (the 'House') which is the 12V distribution/breaker panel.

The Owners manual states that for normal operation, the #1 (PORT) switch always remains connected to the #1 (PORT) battery and the #2 (STBD) switch always remains connected to the #2 (STBD) battery.

In the event either battery is too depleted to start an engine, the selector switch for that engine can be set to start from the other battery or both. Once started, the switches are to be restored to their normal positions.

If either 105A alternator is lost, the selector switches can be used to cross connect as needed to charge both batteries from the functioning alternator until repairs can be made.

In normal operation though, with the both engines running, the charging systems are isolated so there is no chance of feedback from either the alternators or batteries causing over or under-charging.

There is also a completely independent GRP 24 FLA start battery for the generator which is maintained from Bank #3 on the battery charger.

If I find the 'Cabin' or 'House' battery capacity is not sufficient, I will probably double the size of that Bank by adding another 4-D in parallel.

Does anyone see any problems with leaving it this way, without ACR's, combiners, isolators etc.? Again, I mostly day cruise with occasional evenings, or perhaps a weekend at anchor. I have a generator for cooking, charging, air conditioning - and the like.
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Old 04-20-2017, 08:02 PM   #20
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Quote:
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On a boat of your size I would suggest you simplify. Four banks is major overkill on a sub 40' boat...

You're lugging around far too much "dead lead" that can be put to significantly better use when placed into a house bank and actually used "live lead" instead of sitting there at 99.5% + SOC all the time.
I really like this concept. I have a lot of battery capacity on my boat that is unused almost all the time. I have a large bank for my windless/thrusters. I have a relatively large (4D I think) agm start battery for the main, and a group 31 start battery for the genset.

I am going to have to do some thinking about ways to simplify this and maybe get more utility out of the all that weight.
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