1/BOTH/2/OFF Switches Thoughts & Musings
- Thread starter Maine Sail
- Start date
I read and understand the relevance of keeping the house all in one bank but that presents certain problems in my 34ftr.
I was hoping to split the house+start into two equal banks with the ACR for charging to the both and thus having an equal bank in reserve; switching between the two. No designated start bat. Would that detract quantatively from the efficiency of one big bank?
geez....the older I get the less sense I make.....had to edit that 3x.
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The first one was on a friend of mines 65ft sport fisherman, we were out about 75 miles and a problem with the house bank SOC going down. We didn't think to much about it because the bank was over 8 years old and due to be replaced. The start bank was less than a year old.
All of a sudden the house bank went dead and went to switch over to the start bank, and the switch welded and smoke started to fly. Luckly I had my cable cutters along, because we had put new cable on the downriggers, cut the cable and killed the cutters.
What caused the short, the plastic cable hangers that held up the pos cable from the house bank broke and it came down on the transmission output shaft. When the insulation war thru it blew the fuse to the house bank. When I went to switch to the start bank the short caused the switch to weld, the start bank wasn't fused.
The other time, was on my Grady, and was pure stupidity. Was moving the house bank, and had switched on the start bank to run the radio, and the work light, when I was snaking the battery cables to make it easy I tied the two together and fished them thru. It was late so desided to call it a day and switched the bank off. The start bank was fused 250 amp, which blew and kept any damage from happening, except the switch welding.
All of a sudden the house bank went dead and went to switch over to the start bank, and the switch welded and smoke started to fly. Luckly I had my cable cutters along, because we had put new cable on the downriggers, cut the cable and killed the cutters.
What caused the short, the plastic cable hangers that held up the pos cable from the house bank broke and it came down on the transmission output shaft. When the insulation war thru it blew the fuse to the house bank. When I went to switch to the start bank the short caused the switch to weld, the start bank wasn't fused.
The other time, was on my Grady, and was pure stupidity. Was moving the house bank, and had switched on the start bank to run the radio, and the work light, when I was snaking the battery cables to make it easy I tied the two together and fished them thru. It was late so desided to call it a day and switched the bank off. The start bank was fused 250 amp, which blew and kept any damage from happening, except the switch welding.
Other than it not being optimum efficiency charging etc, is there any other down side?
As I can monitor the SOC and switch banks earlier and take lower useable capacity?
Maybe I will just stick with the 2x 6v house & 1x12v reserve in the interim and just get sailing.
If I need more ahrs I will deal with it later.
Many thanks for your help.
Yes, it will cost you more money if they are in 2 banks.
It is unlikely you will switch earlier. If you switch daily the bank of 2 will be drawn down more than the bank of 4 with the same loads.
You shouldn't add to the bank of 2 later. All batteries in a bank should be the same age.
Buy a bank of 4 and you're finished. They will last longer and no switching is required.
How are you charging?
55A alternator going to upgrade to 90A & keep 55 as spare.
200Watts solar
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Yes, most sport fishing boats with start banks are not over-current protected on the start bank however the cables should be sheathed or in conduit and wire support in engine bays should be metal for the exact reasons you illustrated..
As for the Grady blowing a 250A fuse and welding the switch, the switch must have already been on its last legs and borderline arcing already...
Even the medium duty Perko is rated for 250A continuous and for short starting duration's, or the time it takes to trip a fuse, upwards of 1000A-1200A... The equivalent Blue Sea switch is rated at 350A continuous, 1000A for 1 minute and 2000A for as long as 10 seconds. A 250A fuse is long-gone by 10 seconds at 200A... A Blue Sea MRBF 250A fuse will trip in about 0.85 seconds at 875A. My point is that a battery switch should not be welding, if protected by a 250A fuse, unless something is wrong with it..
I've blown hundreds of fuses in testing for the lithium battery standards committee I am on and used a cheap used battery switch to blow well over 100 fuses, all size 300A and up. The switch still works fine and was used, as opposed to a knife switch, to duplicate a boats electrical system with an LFP bank,..
Here is a 300A fuse blown using 15' of 8GA wire and a cheap well-used Guest battery switch. The current behind it was a 400Ah LiFePO4 battery.. The trip current exceeded the inrush capability of my Fluke meter, which is 1000A... This was the first time I did this with 8GA and that switch is still working today. FWIW I am not a huge fan of either the Guest or Perko switches but if I had to choose one over the other it would be the Guest switch, especially their heavy duty versions. I pretty much stick to the Blue Sea switches which have had far more abusive testing done to them than the other brands...
Stick with the largest contiguously wired house bank you can fit and a reserve or start battery that can do double duty as a house bank if needed in a pinch.
The rub is that with lightly built flooded 12V batteries, which are really adapted/modified car batteries from the 50's, you will have a higher likely-hood of having a cell short than you would with 6V golf car batteries. Gold cart batteries are actually designed from the ground up for deep-cycling and are designed for a very abusive environment. If you lost a 6V battery this is what your start or reserve bank is for. This is why I recommend using a deep-cycle version (pseudo deep cycle) of a 12V G-24, 27 or 31 over a starting version of the same group size...
What is a Deep Cycle Battery
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Yes, it's not just about the charging efficiency - the discharge efficiency (and therefore usable Amp hours) is also greater for a single larger bank. Look at the AH ratings for a typical battery - they list them at different rates of discharge relative to the total capacity. If you have one large bank at a given load, it'll last longer than two smaller banks at the same load.
That's correct. There is not a logical reason to go with 2 separate banks. In every way a larger bank is better. If they are in different locations wire them as one, taking negative from 1 pair and positive from the other pair.
Maine, not sure if I saw this, but for the new boaters just starting out and using two battery banks (House and Starter) connected to the 1/BOTH/2/OFF switch, when would that boater be allow to change the switch? For example, if the boater is sailing along and is using solar power for charging, can the boater switch the banks. Same thing applies to a boater who is running on the motor, can the boater change banks?
I would think a truth table of conditions allowing/disallowing the (new) boater to change banks would be beneficial.
I would think a truth table of conditions allowing/disallowing the (new) boater to change banks would be beneficial.
With most any newer battery switch they are "make before break". As long as you don't pass through the OFF position they can be switched when charging. As switches age, or perhaps the builder used cheap switches, they may no longer be "make before break".
That said I generally don't advise switching when charging, if the alternator passes through the battery switch because humans make mistakes...
Here's why:
IS IT BETTER TO HAVE ONE OR TWO BATTERY BANKS FOR HOUSE USE?
(By Nigel Calder - I DIDN’T write this!!!)
The popular arrangement of having two house banks alternated in use needs scrutiny before I go any further.
LIFE CYCLES: As we have seen, the life expectancy of a battery in cycling service is directly related to the depth to which it is discharged at each cycle - the greater the depth of discharge, the shorter the battery’s life.
This relationship between depth of discharge and battery life is NOT linear. As the depth of discharge increases, a battery’s life expectancy is disproportionately shortened. A given battery may cycle through 10% of its capacity 2,000 times, 50% of its capacity 300 times and 100% of its capacity around 100 times.
Let’s say, for arguments sake, that a boat has two 200-ah battery banks, alternated from day to day, with a daily load of 80 Ah. Each bank will be discharged by 40% (80 Ah of one of the two 200 Ah banks) of its capacity before being recharged. The batteries will fail after 380 cycles, which is 760 days (since each is used every other day). If the two banks had been wired in parallel, to make a single 400 Ah battery bank, this bank would have been discharged by 20% of capacity every day, with a life expectancy of 800 days, a 5% increase in life expectancy using exactly the same batteries!
But now let’s double the capacity of the batteries, so that the boat has either two 400 Ah banks, or a single 800 Ah bank, but with the same 80 Ah daily load. The two separate banks will be cycling through 20% of capacity every other day, resulting in a total life expectancy of 1,600 days. Doubling the size of the battery banks in relation to the load has produced a 210% increase in life expectancy. The single 800 Ah bank will be cycling through 10% of capacity every day, resulting in a life expectancy of 2,000 days - a 25% increase in life expectancy over the two (400 Ah) banks, and a 250% increase in life expectancy over the single 400 Ah battery bank!
There are two immediate conclusions to be drawn from these figures:
1. For a given total battery capacity, wiring the (house) batteries into a single high capacity bank, rather than having them divided into two alternating banks, will result in a longer overall life expectancy for the batteries.
2. All other things being equal, any increase in the overall capacity of a battery bank will produce a disproportionate increase in its life expectancy (through reducing the depth of discharge at each cycle).
FOR BATTERY LONGEVITY, A SINGLE LARGE (HOUSE) BANK, THE LARGER THE BETTER, IS PREFERABLE TO DIVIDED (HOUSE) BANKS.
Bruce:
That's the basic reason to get the alternator output OFF the C post of the 1-2-B switch and run it to the house bank. Use either a VSR (combiner or echo charger) to charge the reserve bank, or use B on the switch when charging WITH THE ALTERNATOR, and then switch to the house bank when the engine stops and the alternator is not running.
The reason is that if the alternator output is interrupted the diodes can fry.
WADR, this is covered in Page 1 of this great discussion, the whole reason it was started by Maine Sail in the first place.
Can someone tell me how the below device compares to an ACR/VSR. It came installed in a Used Freightline Sprinter I bought for work. The previous owner was a marine diesel mechanic, so I figure it came off of a yacht at some point.
I am not running a second battery bank in my truck, so I would like to repurpose this on my Hunter 31. How would you wire this in with two banks and a 1-2-both-off switch? Would this work with the standard Hitachi alternator on my Yanmar 2GM. Someone mentioned issues with exciting the coils in another forum.
I am not running a second battery bank in my truck, so I would like to repurpose this on my Hunter 31. How would you wire this in with two banks and a 1-2-both-off switch? Would this work with the standard Hitachi alternator on my Yanmar 2GM. Someone mentioned issues with exciting the coils in another forum.
It appears to be what is called an isolator. It separates two battery banks when charging stops. They are way old technology and induce a voltage drop of up to a volt, not helpful when charging. ACRs are replays that do not induce voltage drop. Don't use it.
Unless you wanna go back to the 60s.
Unless you wanna go back to the 60s.
An ACR doesn't have voltage loss. The isolator you show has about .7 volt loss. If you have an external alt regulator with battery voltage sensing it is fine. Otherwise an ACR is a much better option.
There is nothing good about diode isolators.... Re-purpose it as a boat anchor or garden ornament..
OK, Good to know. Looks like I'm shopping for an ACR/VSR.There is nothing good about diode isolators.... Re-purpose it as a boat anchor or garden ornament..