Re: Basic Battery Wiring Diagrams - II

[Mark Elkin]

This comes from this topic, Basic Battery Wiring Diagrams:  http://c34.org/bbs/index.php/topic,6604.0.html  

I separated it because I use the original topic as a link for others for information.  This is a helpful discussion for alternative ideas, that warrant discussion as different ways to do things, but do not reflect my intention of KISS.  - Stu  10/22/2011  

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Interesting.  Especially because I chose OPTION 3 for Y.Rose.

Two switches.  A simple and highly visible ON/OFF for the house battery bank, which send power to the DC distribution panel.  And a out-of-sight but easily accessed OFF-1-2-BOTH switch for selecting the source of power to start the engine.  (1=dedicated starting battery only, 2=house bank only.  Both and Off are self explanatory.)  

My logic is as follows:
Different battery technologies for each application.  Large (~300 AH) bank of deep cycle Gel cells for house bank, and "ordinary" wet cell with high cold cranking amps for starter.  Alternator output goes to house bank.  Balmar "Duo Charger" gets input from house bank and output charges the starter battery.

The switch circuit I describe above then facilitates....

• House bank is normal choice for the house power.
• Starter battery normally connects to starter and remains isolated from house bank.
• Make it very difficult to use starter battery to power the house systems.
• Make it easy to use house bank either alone or to combine (boost) the starter.

So using just an ON-OFF for the house bank switch is nearly foolproof.  I (or especially, my guests) have only one simple, obvious action to get power to the house systems.  And that simple On-OFF action alone can NOT power the house systems from the starter battery.  So the chance of accidentally selecting the starter battery to power the house and thus draining that crucial battery is virtually nil.

When I want to run the engine, the starter power selector switch is normally set to the starter battery only position.  This keeps it isolated from the house bank but ready at any time to start the motor.  If the starter battery does not have enough power for any reason though, I can choose to combine with or substitute the house bank.  If I did so, it would be a very conscious choice and ss soon as the engine is running, I would return the switch to the normal position.  And since this switch is not in a high visibility area, there is very little chance my guests would accidentally (or purposely) change it.

A slightly outdated, but still accurate diagram is near the bottom of the Project Wiki page: http://www.c34.org/wiki/index.php?title=Electrical_System_Upgrade_-_Yorkshire_Rose.

As Ron so often says, "your boat, your choice".

[Mark Elkin]

Interesting.  Especially because I chose OPTION 3 for Y.Rose.

• Make it very difficult to use starter battery to power the house systems.
• Make it easy to use house bank either alone or to combine (boost) the starter.

Mark, good point.  It's not really a third option, because what you've described is operationally exactly the same as the the dual circuit concept but with two switches, and with exactly the same deficiencies I've edited in the quote from your post.

I agree, the skipper REALLY has to understand how to choose and then how to use his system.

Interesting.  Especially because I chose OPTION 3 for Y.Rose.

• Make it very difficult to use starter battery to power the house systems.
• Make it easy to use house bank either alone or to combine (boost) the starter.

Mark, good point.  It's not really a third option, because what you've described is operationally exactly the same as the the dual circuit concept but with two switches, ...

No, it is not the same as the Blue Seas Dual Circuit concept.  In the BS-DC implementation, the operator only has two options:
1. concurrently activate both the starter and house circuits as isolated circuits, or
2. combine all circuits.  

My arrangement has different options:
1. Turn on the house bank while leaving the starter bank turned off.
2. Turn on the starter bank while leaving the house bank turned off.
3. Turn on both but keep them isolated.
4. Turn on and cross connect both.
5. Leave the starter battery disconnected.  Use house bank for just starting the engine.
6. Leave the starter battery disconnected.  Use house bank for house load AND starting the engine.

... and with exactly the same deficiencies I've edited in the quote from your post.

The only deficiency I have is the ability to use just the starter battery alone to power the house loads.  But this would only be an issue if there was a serious problem with the house battery bank.  And if that was the case, the bad battery could be disconnected or the whole bank disconnected by removing the appropriate power fuse.  Now if the house bank was merely drained, I don't have a problem.  I just start the motor and the house bank would begin to recover as soon as the alternator was generating power.  My alternator has been upgraded and is spec'ed for 110A max.  I don't realistically think it would be able to sustain that, but at the same time, my house bank would probably only absorb 60A during initial bulk changing phase (20% x 300 AH), so I have spare amps to run the house loads even with drained and charging house batteries.

I agree, the skipper REALLY has to understand how to choose and then how to use his system.

Absolutely agree with this.


But then again, we DO seem to have philosophically different viewpoints of the purpose for the #2 battery bank and circuit.  You describe it below as a "reserve bank".  I think of it as the "starter battery".

Conceptually, I simply disagree with these electrical system "design criteria" and would always want to have the ability to power LIMITED LOADS from the reserve bank WITHOUT COMBINING the two banks, which can easily be done with the two systems described above.  Maine Sail made the case and explained the downside of combining banks in his referenced link in my last post.

Why?  Because it is the HOUSE bank that is much more likely to be drawn down than the reserve bank.

Granted.  And the BS Dual Circuit switch is not the answer, for all the reasons Maine Sail describes, and you and I agree both with.


And there is a subtle point to my design that I think was overlooked earlier.  My variation of OPTION 2 attempts to reduce the impact on the battery banks when human error occurs.  For identification, lets call the original description you posted OPTION 2A, and call mine 2B.

In 2A, there is a greater chance for casual human error to accidentally draw down the "starter" battery.  All it takes is someone accidentally setting the [main] 1-2-B switch to the starter/reserve bank (or the Both) position when turning on power to the house DC distribution panel.  Then the only way to get sufficient power to the starting motor is to either combine the weak and strong banks (which has the very problems described in the previous threads), or to disconnect the weak bank's battery cable first and then move the selector switch to "B" to get the strong bank to the starter circuit.

In 2B, there is no chance for casual human error to draw down the starter battery when turning on house power.  It takes a specific and less likely set of actions to make that mistake.  Yes, it is possible, but far less likely to be left without the ability to start the motor and recharge the batteries.

Good to see you back and active.

Sometimes life throws just too much stuff in our path and we just have to focus our limited time and energy resources.  I have finally managed to shovel some of that stuff to the side.  It is good to be back and active here again.[/list]

[mainesail]

In 2A, there is a greater chance for casual human error to accidentally draw down the "starter" battery.  All it takes is someone accidentally setting the [main] 1-2-B switch to the starter/reserve bank (or the Both) position when turning on power to the house DC distribution panel.  Then the only way to get sufficient power to the starting motor is to either combine the weak and strong banks (which has the very problems described in the previous threads), or to disconnect the weak bank's battery cable first and then move the selector switch to "B" to get the strong bank to the starter circuit.

That is not true in 2A. Simply flip the ON/OFF to OFF and turn the 1/2/BOTH/OFF to BOTH and you have now totally isolated the #2 battery and can start off the house loads without combining the banks to do so. You also still have the ability to use the start/reserve bank to power house loads in the event a bank fails too all without combining a good bank with a bad bank.. Which happened to a customer of mine two weeks ago and he lost both banks all thanks to the Dual Circuit Plus switch...

I have replaced around 60 batteries since June with nearly 12 (3 banks) of them being sudden and catastrophic failures, mostly AGM's with the sudden failures, I truly understand why I want my customers to have the redundancy I try and wire for.

I also wire them up as 2B or 2B variants using the ON/OFF as house. Did this yesterday on an off shore racing boat, a Sydney 38. The starter cable was only long enough to reach the 1/2/BOTH/OFF and no dire need to pop for more 2/0 wire if not absolutely necessary, plus the weight thing..... 

Both methods can still have HEF (human error factor) issues so proper labeling of the switches is very important. I am not a huge fan of hidden switches as I was on a race boat when an electrical fire started. I was the one to dive below and immediately flip the battery switch to off which stopped the meltdown. Thankfully that switch was well placed. While there yesterday I also started the 3GMF on this race boat off the dual group 27 house bank of Odyssea batteries and the voltage dip was 12.3V under starting loads from a resting voltage of 12.6. Odyssea's are amazing that way. Seeing as this is an ultralight racer the dedicated starting battery is a very small & lightweight  Odyssea that is about the size of a lawn tractor battery. Even that little thing supported 11.0V under full starting load. Of course the in-rush on the 3Gm is under 250A and average is about 125A for just a few seconds..

The far easier solution is to just do everything off the house bank and use the existing switch..

P.S. Installed a battery monitor for a customer today and discovered his house bank to be complete toast. When the yard wired it this spring they mixed the leads for the older model ACR and got them backwards. With the DCP the charge current was wired to feed the start battery then combine with the house through the ACR. It never combined and the alternator had not charged the house bank since at least late June. All he had was a small trickle solar panel of maybe 20 watts... I have the bank on the bench tonight for equalize and charge, it was new last season. I'll see if we can salvage them for the remainder of this season. I suspect it will be another dead bank due to sloppy wiring.. Thank god Blue Seas changed the sensing on their ACR's to A & B as opposed to just bank A. Sadly this is about the fourth or fifth time I have seen this with the older DCP kit...

[Mark Elkin]

Maine Sail,
My apologies.    I rushed through Stu's original written description of Option 2(A) and didn't stop to look at your diagram.  That's the problem with being overloaded by "stuff".

I see now that I over-estimated the chances casual human error causing the starter battery to be drained by the house bank.  In both our schemes (2A and 2B), the chance is still there.  In both, it takes more than a single mistake to cause that specific problem to occur.

Mark