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Old 28-12-2017, 01:02   #1
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Shunt wiring

Always something to learn!

My xantrex lite seemed to be inaccurate (Ah) the other morning. I've been meaning to give all the terminals and connections around the battery a good clean for a while . The little screws that attach the the xantrex to the shunt didn't look great. Anyway they snapped off completely upon undoing them.

My understanding is a shunt provides a small resistance to current and the tiny voltage drop is measured and the meter magically determines current in and out?

The option to fix them in the original position is no longer. I put bigger terminals on them and attached them to either end of the shunt where the negative wires attach. Obviously dosent work, meter told me I was pulling 32A,which is about 30A to much!

I'm assuming the distance between the wires on the shunt matters, the meters calibrated to a certain distance between the wires ?? I actually have no idea, anyone know?

Also, I'm purchasing a new battery monitor for my bluesky regs, although it comes with a new shunt it doesn't come with the twisted wire. The wire I'm currently using isn't long enough to reach where I need to put the monitor.

My question, wire is the wire twisted? Can I get any thin wire and twist it up with a drill? Or is there something special about that particular wire?

It's difficult for me to get some stuff in the Seychelles, there's no zip code so online buying systems don't accept any my orders. Defender is great, their customer service via email gets me most things, but not all.

Thanks in advance.
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Old 28-12-2017, 01:29   #2
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Re: Shunt wiring

Quote:
Originally Posted by daletournier View Post
Always something to learn!

My xantrex lite seemed to be inaccurate (Ah) the other morning. I've been meaning to give all the terminals and connections around the battery a good clean for a while . The little screws that attach the the xantrex to the shunt didn't look great. Anyway they snapped off completely upon undoing them.

My understanding is a shunt provides a small resistance to current and the tiny voltage drop is measured and the meter magically determines current in and out?

The option to fix them in the original position is no longer. I put bigger terminals on them and attached them to either end of the shunt where the negative wires attach. Obviously dosent work, meter told me I was pulling 32A,which is about 30A to much!

I'm assuming the distance between the wires on the shunt matters, the meters calibrated to a certain distance between the wires ?? I actually have no idea, anyone know?
It is calibrated to the resistance of the shunt e.g. an 100 Amp shunt might produce a voltage drop of say 50 mV (or perhaps 75 or even 100 mV)
Also, I'm purchasing a new battery monitor for my bluesky regs, although it comes with a new shunt it doesn't come with the twisted wire. The wire I'm currently using isn't long enough to reach where I need to put the monitor.

My question, wire is the wire twisted? Can I get any thin wire and twist it up with a drill? Or is there something special about that particular wire?
Yes
It's difficult for me to get some stuff in the Seychelles, there's no zip code so online buying systems don't accept any my orders. Defender is great, their customer service via email gets me most things, but not all.

Thanks in advance.
Sorry don't have time right now to write more: others will chime in and expand the information.
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Old 28-12-2017, 01:51   #3
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Re: Shunt wiring

If the meter is reading significantly more amps than it should, that means it is seeing a larger voltage drop across the sense wires. This can be caused by poor connections at either end.
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Old 28-12-2017, 02:05   #4
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Re: Shunt wiring

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If the meter is reading significantly more amps than it should, that means it is seeing a larger voltage drop across the sense wires. This can be caused by poor connections at either end.
Hi Paul, I've put the connectors on top of the negative cables, was just thinking this would be extra resistance. I'll put them at the bottom this afternoon and see if there's a difference. It's a temporary thing until new monitor turns up, if I can get around the zip code thing.
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Old 28-12-2017, 02:25   #5
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Re: Shunt wiring

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Originally Posted by daletournier View Post
Hi Paul, I've put the connectors on top of the negative cables, was just thinking this would be extra resistance. I'll put them at the bottom this afternoon and see if there's a difference. It's a temporary thing until new monitor turns up, if I can get around the zip code thing.
Make sure the crimps are good and clean the studs and connector.
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Old 28-12-2017, 02:47   #6
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Re: Shunt wiring

Quote:
Originally Posted by Paul L View Post
Make sure the crimps are good and clean the studs and connector.
I do not know what type of shunt you have, but I assume the resistor wire in the shunt has a bad connection to the terminals, so internal resistance is higher and therefore the voltage drop is higher too. If you cannot fix it by cleaning and fastening of the terminals you probably will need to replace the shunt.
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Old 28-12-2017, 02:48   #7
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Re: Shunt wiring

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Make sure the crimps are good and clean the studs and connector.
Will do. It sounds crazy but there's some simple stuff I just haven't got around to yet. Purchased the boat 12mths ago, quick refit, made sure I was happy she was safe and then took off across the Indian ocean, I've been cruising full time since, approximately 7500nm. I'm now on the boat alone for two mths and plan to do all the little jobs that I haven't got around to, not going to move,looking forward to it.
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Old 28-12-2017, 05:28   #8
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Re: Shunt wiring

Thanks guys, sorted. Simple clean up of terminals Duh!
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Old 28-12-2017, 05:47   #9
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Re: Shunt wiring

My Victron does not have twisted wire for the shunt to meter.
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Old 28-12-2017, 06:56   #10
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Re: twisted Shunt wiring

The reason the wire is twisted is to provide resistance to interference from radio transmissions - primarily HF (SSB). If you don't have an SSB or you don't see the current meter go wild when you transmit, don't worry about it

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Old 28-12-2017, 07:37   #11
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Re: Shunt wiring

Ive also seen them insulated like coaxial cable, silver foil insulation.
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Old 28-12-2017, 07:56   #12
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Re: Shunt wiring

CAT5e cable is shielded twisted pair cable (4 pairs), also telephony cable is TP.
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Old 28-12-2017, 10:34   #13
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Shunt wiring

Quote:
Originally Posted by daletournier View Post
Hi Paul, I've put the connectors on top of the negative cables, was just thinking this would be extra resistance. I'll put them at the bottom this afternoon and see if there's a difference. It's a temporary thing until new monitor turns up, if I can get around the zip code thing.


This will not work. There are 4 connections to a shunt. 2 are high current connections. 2 are just for measuring the voltage which is related to current. The big connections can never give the right voltage and the current measured will always be wrong and and it will vary too much with temperature.

Either fix the small broken connections or get a new shunt.
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Old 28-12-2017, 10:46   #14
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Re: Shunt wiring

Like others have said, the wire doesn't need to be twisted unless you are picking up interference from a SSB or other device on the boat that is creating radio interference. You can reuse the old twisted wire and just extend it a few inches or feet if it isn't long enough to reach the new shunt using untwisted wire and it shouldn't make much of a difference over that short untwisted distance.

You can also twist wire with a battery drill if you want to as well to create a twisted duplex (or triplex, whatever.) The rate of twist in the wires is calculated not to be "in tune" with the frequencies they are trying to suppress. If you count the number of twists over given number of inches or cm, you can replicate the twist fairly closely if your wire will hold the twist after it is wrapped. Some wire tends to spring back some, some springs back a lot and won't hold a twist. It depends on how many and how fine the strands are inside. Be aware that if you make your own twisted wire it will 'shrink' when it is twisted and not reach as far since it is now taking a spiral path instead of a straight line from point A to point B. The amount of shrinkage can be significant so be sure to buy extra wire if you make your own twisted cable runs.
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Old 28-12-2017, 12:22   #15
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Re: Shunt wiring

I have a little bit unrelated question. Is a shunt generic other than amp rating? Can a various amp meters be connected to a shunt? Only one connected at a time of course.
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