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Go Back   SailNet Community > On Board > Gear & Maintenance > A/B switch for removing shut from battery circuit
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Thread: A/B switch for removing shut from battery circuit Reply to Thread
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Topic Review (Newest First)
10-11-2009 01:22 PM
mitiempo motion300
If you're asking if the starter current goes through the meter, no it just goes through the shunt. The shunt has to be the first connection of the negative line directly from the battery post.
Patrick
I agree with Maine Sail about the monitor, unless you can replace the shunt with a bigger one which would be the easiest and would allow you to keep the display you like. As long as the shunt you get is the same ratio (50mv/500v, etc.) I see no reason it wouldn't work. Maine Sail?
Brian
10-11-2009 01:03 PM
motion300 on the victron meter does on run the starter and the thruster through the battery monitor?
02-23-2009 04:25 PM
patrickstickler
Quote:
Originally Posted by patrickstickler View Post
A main reason why I'll stick with the Nasa BM-1 is I *love* the display. Easy to read from pretty much anywhere in the cabin, and shows voltage, current flow, percentage bar and hours to empty at the same time. ...
Oops. You do actually have to push a button to get the time to empty. But it's still a nice display...
02-23-2009 04:15 PM
patrickstickler
Quote:
Originally Posted by Maine Sail View Post
Sorry for being a contradictory view point but I would personally take a different approach. I would spend the money and buy a true battery monitor like the Victron BVM-600 (LINK). This monitor comes standard with a 500 amp shunt for $194.65. The Xantrex Link Lite is also another option.
A main reason why I'll stick with the Nasa BM-1 is I *love* the display. Easy to read from pretty much anywhere in the cabin, and shows voltage, current flow, percentage bar and hours to empty at the same time. All the others I've looked at have tiny displays and need to be cycled though different views to get all the info.

What can I say... I like clear and easy to read instruments ;-)

Quote:

By the time you're done buying battery cables, DPDT or DPST, switches or high amp battery switches, and building a by pass for a 100 amp shunt, you could have yourself a beautiful new battery monitor that will give you lots more information and for not a lot more money than a by-pass.

Out with the old and in with the new would be my suggestion. I've yet to meet any boater, though I'm sure they are out there, who's installed a battery monitor and properly calibrated it that regretted it.
I've pretty much decided to take Bene505's advice and keep it simple -- and keep the two circuits separate. I hadn't actually had any problems with the starting battery, but was just used to having an A and B option (moved from two matched flooded start-and-house batteries to a single flooded starting battery and house bank of AGMs). I guess I was just too stuck to adopt a different point of view on the arrangement. Always nice to have one's point of view unstuck ;-)
02-23-2009 04:10 PM
btrayfors Just put a simple ON-OFF switch in to short out the shunt (effectively bypassing it). OFF is normal. ON shorts out the shunt and allows you to pass whatever amperage the switch/cabling is rated for.

Bill
02-23-2009 01:39 PM
Maine Sail
Sorry for

Sorry for being a contradictory view point but I would personally take a different approach. I would spend the money and buy a true battery monitor like the Victron BVM-600 (LINK). This monitor comes standard with a 500 amp shunt for $194.65. The Xantrex Link Lite is also another option.

By the time you're done buying battery cables, DPDT or DPST, switches or high amp battery switches, and building a by pass for a 100 amp shunt, you could have yourself a beautiful new battery monitor that will give you lots more information and for not a lot more money than a by-pass.

Out with the old and in with the new would be my suggestion. I've yet to meet any boater, though I'm sure they are out there, who's installed a battery monitor and properly calibrated it that regretted it.
02-23-2009 12:59 PM
GordMay
Quote:
Originally Posted by patrickstickler View Post
My understanding is that it's not so much a matter of taking the ammeter out of the circuit, but taking the entire shunt out of the circuit. I.e., even if you disconnected the low current ammeter wires from the shunt, you'd still be running ~400A through a shunt that is rated at 100A max, and the docs state that doing so can permanently alter the characteristics of the shunt ...
Patrick is entirely correct. I apologise for my misleading & inaccurate post.
02-23-2009 12:08 PM
Bene505 Is having a dead starting battery so much of an issue that your really want to put a dedicated switch in place to do a bypass?

I'd attack the problem in two ways 1) focus $ and effort on the problem rather than the symptom. 2) Have a plan B. For one thing you won't have to buy as many starting batteries over time.

1) Attack the real problem. Find the source of the drain on the engine battery, using a multi-meter. Then, to help keep the starting battery charged, wire a small solar cell to support the engine battery. A small one will not need a voltage controller. It will maintain the voltage, and will even provide a small bit of charging. Think about a cell that is about 1/2 square foot in size. They sell them for this purpose, and I've seen sailboats with a solar cell built-in for this purpose.

2) For plan B, get a piece of wire that you can use as a jumper cable. Better yet, get a jumper cable. Wherever you go, you can build good karma, jumping your slip-neighbor's batteries or loaning the jumper cables to someone with a dead car battery. You may even get a beer out of it.

[Since for me, a dead engine battery happens before a trip and not usually during, there's no need to rush anything with a large amount of current all at once. I sometimes use a 5 foot long piece of normal speaker wire that I happen to have. It won't help if the engine battery is truly dead, but after waiting awhile, it get's the starter battery up to the point where it can start the diesel. The wire is long enough to not get hot. That is critical with this approach -- if it gets hot, you need a longer wire. If I need something faster, I'll rig a thicker cable for a jump. That's my method and it might not work for everyone. So it's IMHO.]

IMHO, attack the real problem and have a plan B. You'll keep the system's complexity down and have a plan B that you can apply to other uses.
02-23-2009 10:34 AM
sailingdog You could wire a single pole, double throw (SPDT or A/B) switch in the circuit, and use that to take the shunt off line when you need to start using the house bank. The common terminal of the switch would go to the batteries, and one pole would go to the shunt and the other to the shunt bypass.

Quote:

Setup with both switches in A for normal use:

.............................................Gnd
..............................................|
............|-------------[shunt bypass]------|
............. ................................|
...........(a)------------- Shunt ------------|
............|................................ |
House Bank (+)---------(+) FuseBox (-)--------|
..............................................|
...............--------{a]---(+) Engine (-)---|
...............|..............................|
Starting Batt (+)
........................... |
..............(-)-----------------------------|


Setup with both switches in B for bypass use:
.............................................Gnd
..............................................|
............|-------------[shunt bypass]------|
............| ................................|
...........(b)......------- Shunt ------------|
............|................................ |
House Bank (+)---------(+) FuseBox (-)--------|
........................|.....................|
.......................{b]---(+) Engine (-)---|
..............................................|
Starting Batt (+)
........................... |
..............(-)-----------------------------|


If you had a single, heavy duty double pole double throw switch, it could do it automatically, and prevent any risk of frying the shunt by accident.
02-23-2009 10:30 AM
patrickstickler
Quote:
Originally Posted by patrickstickler View Post
I've worked out a circuit that would do what I need to do with three Blue Sea 6010 switches, but it's not terribly elegant.

I could make things alot simpler if just shorting across the shunt would do the trick.
An A/B switch would be even better.
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