Shunt and general wiring advice (1 Viewer)

[Infinity31]

When looking at installing a battery monitor I found the original wiring to be rather strange, it worked but wasn't correct, see fig 1.

Fig 2 illustrated how I intend to change the wiring to incorporate the shunt. I'm fairly sure it's ok but would rather have someone more competent than me check it over before I have the cables made up.

BTW all the cables were of an appropriate size ie 4mm, 16mm and 25mm and although not shown the solar + will be fused.

Thanks, Chris.

 

[Richard n Ann]

That's how I would do it. Did mine the same but I've only got 1 battery.

 

[Lenny HB]

Fig 2 is the correct way but with 2 batteries next to each other it won't make any real difference.

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[Wissel]

It's been a while since I wired my shunt in, but I do remember it should be wired in before all loads.

As the solar isn't in fig 1, fig 2 is better.

Also fig 2 is using diagonal wiring, which in theory balances loads better between the two batteries. I have four batteries wired this way.

 

[PhilandMena]

I'm not the brightest button in the box when it comes to reading wiring diagrams and consider myself not competent on the subject. However, I do have the wiring diagram for the shunt I fitted (I was walked through it by someone who was competent) and you may find the diagram on page 3 of value.

 

[Lenny HB]

As the solar isn't in fig 1, fig 2 is better.

Correct I missed the solar when I had a quick look.

Also fig 2 is using diagonal wiring, which in theory balances loads better between the two batteries. I have four batteries wired this way.

Yes important for 4 batteries doesn't make much odds with 2 if they are next to each other.

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[Sundowners]

Sorry for my ignorance!!!!-------- what is the shunt for???----- I googled it and it seems like an amp meter?????
Nigel

 

[Infinity31]

Thanks all for confirming I'm on the right track.

Fig 1 is as I found it when investigating where to put the shunt, it includes solar. What I found strange was not seeing diagonal wiring for the two batteries, and the solar going to pos+ and neg- of one battery.
As has been said with them being so close together it probably won't make a difference.

Fig 2 is how I'm going to wire it with the addition of a shunt for the battery monitor. The addition of the shunt is the only difference between the two diagrams, solar is in both.

Thanks again for the help.

 

[andy63]

Sorry for my ignorance!!!!-------- what is the shunt for???----- I googled it and it seems like an amp meter?????
Nigel

The shunt is an inline known resistance and when a current is passed through it there is a volt drop across the resistance...
That volt drop equates to a certain current and the gauge displays the volt drop in amps... ie so many mv equates to a certain amperage flowing.
An effective way of measuring a high current flow without having to pass a heavy current through an instrument.
Andy.

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[PhilandMena]

The shunt is an inline known resistance and when a current is passed through it there is a volt drop across the resistance...
That volt drop equates to a certain current and the gauge displays the volt drop in amps... ie so many mv equates to a certain amperage flowing.
An effective way of measuring a high current flow without having to pass a heavy current through an instrument.
Andy.

Which means you can read the amount of Amps being taken out of and or being out into your batteries in real time.

 

[andy63]

Which means you can read the amount of Amps being taken out of and or being out into your batteries in real time.

Yep.. providing all loads and charging sources are wired to the correct side of the shunt..

 

[pappajohn]

You can save a bit of time and rewiring by fitting the shunt in the existing neg lead between battery and the neg splitter block and moving the neg solar wire to the shunt.
Effectively you only need to cut the neg battery wire and fit the shunt there.
As already said, diagonal battery wiring isn't worth the hassle with two batteries.

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[autorouter]

In Fig 1, the solar charge current will not be seen by the existing shunt. To correct this, you could move the solar negative to the load side of the shunt (ie the side furthest from the battery).

Fig 2 will work with the new battery monitor shunt. However there is a similar problem with the existing shunt. If you move the solar negative to the load side of the existing shunt, then the solar current will register correctly in both the new and existing shunts.

 

[Infinity31]

You can save a bit of time and rewiring by fitting the shunt in the existing neg lead between battery and the neg splitter block and moving the neg solar wire to the shunt.
Effectively you only need to cut the neg battery wire and fit the shunt there.
As already said, diagonal battery wiring isn't worth the hassle with two batteries.

Ideally that is what I wanted to do but there isn't space to mount the shunt in that area.
The batteries are under the drivers seat laid out as in the diagram front to the right, thats where the neg splitter is and it's very tight for space. There's room to mount the shunt is behind the seat next to the solar reg.
If I've got to route the neg lead to the shunt at the back and then to the splitter at the front I may as well diagonally wire while I'm at it.

 

[Infinity31]

In Fig 1, the solar charge current will not be seen by the existing shunt. To correct this, you could move the solar negative to the load side of the shunt (ie the side furthest from the battery).

Fig 2 will work with the new battery monitor shunt. However there is a similar problem with the existing shunt. If you move the solar negative to the load side of the existing shunt, then the solar current will register correctly in both the new and existing shunts.

Sorry my drawing is a bit misleading I know it looks like I've drawn a shunt in fig 1 but there is no existing shunt it's a neg splitter bar

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[autorouter]

In that case, Fig 2 is fine. You could wire the solar negative to the negative splitter bar if that's more convenient.

 

[autorouter]

The reason to use a shunt is to keep the thick main current wires as short as possible. I would try very hard to find a space as near the batteries as possible. The thin shunt wires can be any length, it doesn't matter.

 

[Infinity31]

The reason to use a shunt is to keep the thick main current wires as short as possible. I would try very hard to find a space as near the batteries as possible. The thin shunt wires can be any length, it doesn't matter.

Trust me I tried. The space is filled with relays, link fuse and other electrical gubbins, there just isn't room. The neg connecting wires are 45cms and 65cms @ 25sq mm so not that long.

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[Richard n Ann]

Is it a NASA BM2 or BM1 battery monitor? Have you bought it yet? Excellent kit, in addition to the standard voltage and current readings, I've just found there's an AH 'trip' meter on it that you reset to zero and it counts up or down, so you know in any 24hr period if the solar is keeping up with demand. Expensive but top piece of kit.

 

[Infinity31]

Is it a NASA BM2 or BM1 battery monitor? Have you bought it yet? Excellent kit, in addition to the standard voltage and current readings, I've just found there's an AH 'trip' meter on it that you reset to zero and it counts up or down, so you know in any 24hr period if the solar is keeping up with demand. Expensive but top piece of kit.

No not a NASA. I did consider a NASA as I had the BM1 Compact on another van and it was a good relatively inexpensive monitor.

I've splashed out on a Victrom BMV-712 Smart. It has an auxiliary input so starter voltage can be displayed plus bluetooth in integral so no need to use a VE direct dongle to connect to a mobile phone.
It also has much reduce current draw compared with previous BMV's

 

[Richard n Ann]

No not a NASA. I did consider a NASA as I had the BM1 Compact on another van and it was a good relatively inexpensive monitor.

I've splashed out on a Victrom BMV-712 Smart. It has an auxiliary input so starter voltage can be displayed plus bluetooth in integral so no need to use a VE direct dongle to connect to a mobile phone.
It also has much reduce current draw compared with previous BMV's

An excellent choice sir I like the idea of Bluetooth but in my case I'd be distracted when driving so maybe it's a good thing the BM2 hasn't got it . I went off Victron when my 475w pure sine wave wouldn't run my hair clippers. I'm pleased you haven't bought a piece of Chinese junk anyway

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[Tykatem]

Is it a NASA BM2 or BM1 battery monitor? Have you bought it yet? Excellent kit, in addition to the standard voltage and current readings, I've just found there's an AH 'trip' meter on it that you reset to zero and it counts up or down, so you know in any 24hr period if the solar is keeping up with demand. Expensive but top piece of kit.

Hi Richard, i've just bought a NASA BM1 and on reading the installation pamphlet it says I need to run an earth lead from the engine start battery to the shunt supplied with the kit. Question, is there a max length that the earth lead should be?

Pete

 

[Richard n Ann]

Hi Richard, i've just bought a NASA BM1 and on reading the installation pamphlet it says I need to run an earth lead from the engine start battery to the shunt supplied with the kit. Question, is there a max length that the earth lead should be?

Pete

I don't think I did that. The engine earth/chassis is the same as the leisure battery earh/chassis so it would be pointless. I'll see if I can look the diagram up.

 

[Richard n Ann]

It's a greyed dotted line meaning it should be an existing connection, ie chassis (but if it isn't you need to fit it, so it's on the diagram)

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[pappajohn]

Duplicate post.

 

[Lenny HB]

I don't think I did that. The engine earth/chassis is the same as the leisure battery earh/chassis so it would be pointless. I'll see if I can look the diagram up.

Should already be connected for split charging.
Looking at the diagram you posted I take it the BM1 is capable of measuring starter batter charge as well, if so the lead would need reconnecting to the shunt.

 

[DBK]

Hi Richard, i've just bought a NASA BM1 and on reading the installation pamphlet it says I need to run an earth lead from the engine start battery to the shunt supplied with the kit. Question, is there a max length that the earth lead should be?

Pete

You don't need to do that unless you want to monitor the starter battery, which I don't see much point in doing in a typical MH setup. It is the leisure batteries you want to monitor. This is covered in the instruction leaflet which was linked to earlier.

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[Infinity31]

As has been said the neg is already connected by way of the leisure battery neg.

The fused "This cable is not supplied" facilitates starter battery monitoring.