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Old 09-02-2016, 12:05   #1
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Looking for DC current transformer rather than Shunt

Is anyone aware of a DC current transformer which could be used with with the xantrex Link 20. The Link 20 expects 50mV @ 500A. I'm just not keen on adding a Shunt to my bowthruster/windlass battery due to it's high current.

I've been able to find AC ones, but not DC ones.

Background Links:
https://www.bluesea.com/products/807..._Coil_-_50A_AC
Link 20:
http://www.xantrex.com/documents/Dis...196-01-01).pdf
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Old 09-02-2016, 12:19   #2
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Re: Looking for DC current transformer rather than Shunt

Why would you not want to use a shunt? if the shunt is rated for 500 amps that should be fine. all your ammeter does (in reality) is measure volts. a 500amp 50mv shunt just reads 50mv by the meter (at 500amps of current passing through the shunt) . your windlass battery wont even notice the shunt.
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Old 09-02-2016, 12:31   #3
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Re: Looking for DC current transformer rather than Shunt

Just so you know, there is no such thing as a DC transformer. A transformer operates on alternating current only.

There are devices that convert DC voltages, but they are not called transformers.
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Old 09-02-2016, 14:33   #4
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Re: Looking for DC current transformer rather than Shunt

Dennis,

You are correct.. after looking at the AC transformers I used that name rather than current transducer or hall effect sensor.
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Old 09-02-2016, 14:39   #5
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Re: Looking for DC current transformer rather than Shunt

Most of the hall effect devices will not work with the link 20 because the link 20 expects the shunt voltage to be negative with respect to battery minus. Most hall effect devices are positive output.

There is no concern with using a resistive shunt. That is what the link 20 is designed to use. It will more accurate and cheaper than a hall device.
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Old 09-02-2016, 14:52   #6
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Re: Looking for DC current transformer rather than Shunt

How are you running your negative from the bow now? Around the shunt and direct to the engine? If so, just put it on the load (not battery) side of the shunt. Issue primarily could be that your thruster/windlass battery is NOT part of the house bank while the Link 20 is dealing with house and reserve/start.

Let us know how you're configured. Running through the shunt should be fine current-wise, but we need more information to help.
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Old 09-02-2016, 15:23   #7
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Re: Looking for DC current transformer rather than Shunt

Not exactly sure about your setup and as the others have indicated adding the shunt is really no big deal. The terminal voltage of the battery will drop a lot more than the shunt drop when you punch that bow thruster (batteries have internal resistance too).

On Cbreeze we have a house bank (4 GC) and 2 more in the bow. Normally they are all just connected in series/parallel. The Emeter shunt is back at the house bank and the windlass and bow thruster are connected to the fwd bank thus bypassing the shunt. I thought about bringing the fwd negative back to the shunt but then that defeats one of the main advantages of the bow battery location. Looked at the numbers and although the bow thruster draws a lot of current (2/3 from the front set and 1/3 main) the time on is short resulting in a rather negligible error in the indicated Emeter AHs. 300 amps for 30 seconds is only 2.5 AH and that is a lot of bow thrusting. If the battery bank is never brought up to the level that the Emeter resets then I suppose the error would gradually build, but in our style of cruising just has not caused a problem. Those AH meters are not real accurate.

Because you Link 20 system is capable of handling two shunts put the second in the bow circuit if you must. As a reference the terminal voltage on the fwd set of GC2s drops almost a volt (1000 mv) when I punch that thruster. Shunt drop is in the noise
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Old 09-02-2016, 15:39   #8
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Re: Looking for DC current transformer rather than Shunt

Quote:
Originally Posted by Frankly View Post
SNIP>>>Looked at the numbers and although the bow thruster draws a lot of current (2/3 from the front set and 1/3 main) the time on is short resulting in a rather negligible error in the indicated Emeter AHs. 300 amps for 30 seconds is only 2.5 AH and that is a lot of bow thrusting. If the battery bank is never brought up to the level that the Emeter resets then I suppose the error would gradually build, but in our style of cruising just has not caused a problem. Those AH meters are not real accurate.

Because you Link 20 system is capable of handling two shunts put the second in the bow circuit if you must. As a reference the terminal voltage on the fwd set of GC2s drops almost a volt (1000 mv) when I punch that thruster. Shunt drop is in the noise
Good points about the ah being actually used.

IIRC, the Link 20 comes with a dual shunt, not two, but same result.

That's why I asked how he's wired. Seems he already has the Link 20 installed. Is this correct?
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Old 09-02-2016, 17:19   #9
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Re: Looking for DC current transformer rather than Shunt

Yes I am already using the shunt (at least 1/2 of the one provided) for the Engine. Since it doesn't look like there is a way I'll go with the Shunt. (I just didn't want to put one in.. for some reason I'm not really comfortable with one at such high amperage (but logically I know they are safe).

Here are the two diagrams for the set-up I have/am putting together:



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Old 09-02-2016, 18:43   #10
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Re: Looking for DC current transformer rather than Shunt

For your proposed set up don't see a compelling reason to know the AH or A draw from the bow battery. Your main interest is just keeping an eye on the fwd battery to make sure that it is getting recharged. The second voltage input on the Link 20 should take care of this. Just tap the front battery using the BS fuse block.

A DC clamp on ammeter to check on the two DC motors from time to time might be a nice preventative maintenance item. No DC transformers but magnetic sensors will give you the current in the wire.

Dig around in the Blue Sea technical info. They did some actual testing on ANL fuses. Turns out that they are really slow blow and maybe should be downsized depending on the application.

I used a manual battery switch for the fwd battery (main bank also). Keep it off when leaving the boat. Cheaper and a little more failure resistant
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Old 09-02-2016, 18:52   #11
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Re: Looking for DC current transformer rather than Shunt

Quote:
Originally Posted by Dennis.G View Post
Just so you know, there is no such thing as a DC transformer. A transformer operates on alternating current only.

There are devices that convert DC voltages, but they are not called transformers.
True: DC-DC Converter - Solid state hocus-pocus. These are some interesting items. Some are very high efficiency and can give you nicely regulated DC from you battery. DC-DC Converter | Murata Manufacturing Co.
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Old 10-02-2016, 00:59   #12
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Re: Looking for DC current transformer rather than Shunt

maretron makes a battery monitor with a wrap around sensor. but I've put one in and it didn't work very well at all.
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Old 11-02-2016, 02:37   #13
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Re: Looking for DC current transformer rather than Shunt

Nearly every new current clamp meter, can measure DC current.
There are model with Current Clamp connected remotely to master instrument.
Belive If your Bow Thruster has intelligent speed controller, it might have current or voltage monitor lines already available .
Good quality voltmeter to monitor bat. condition in respect to load is critical.
My way to measure high current without spending a cent and introducing any shunt or DC coil pick up is this. Any connection between load/ motor and source/ battery
typically creates enough milivolts drop, can be measured .
Is directly proportional current, than just connect milivoltmeter between
+battery and + motor. Using current Clamp Meter to create conversion table.
simple and bulletproof , not introducing any more complex electronic.
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Old 11-02-2016, 05:01   #14
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Re: Looking for DC current transformer rather than Shunt

Quote:
Originally Posted by Tikka View Post
Nearly every new current clamp meter, can measure DC current.
There are model with Current Clamp connected remotely to master instrument.
Belive If your Bow Thruster has intelligent speed controller, it might have current or voltage monitor lines already available .
Good quality voltmeter to monitor bat. condition in respect to load is critical.
My way to measure high current without spending a cent and introducing any shunt or DC coil pick up is this. Any connection between load/ motor and source/ battery
typically creates enough milivolts drop, can be measured .
Is directly proportional current, than just connect milivoltmeter between
+battery and + motor. Using current Clamp Meter to create conversion table.
simple and bulletproof , not introducing any more complex electronic.
Actually MOST clamp ammeters are AC not DC. I've been looking for a DC clamp ammeter for quite a while. they're much harder to find than an AC clamp ammeter.
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Old 11-02-2016, 09:28   #15
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Re: Looking for DC current transformer rather than Shunt

I've had several Fluke AC and DC clamp ammeter/mulitmeters. They work great. The DC function is great for checking alternator outputs and to find which wire is energized for tracing purposes - AC and DC. I was thinking there were some less expensive ones with both AC and DC amps too but haven't looked for them. I used them professionally all the time and now use them on my own boat only, or to help others occasionally.
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