MPPT to battery wiring & shunts

[Cloudinspector]

I'm about to wire in a MPPT solar charge controller and am unsure whether the negative cable can go direct to the batteries or will it need to go via the shunt that's fitted for the BMV battery monitor. At the moment there are no negative connections to the batteries other than the shunt negative and smart gauge negative.

 

[WotEver]

If you want the BMV to see what's going in and out then it should go via the shunt. 

[Robbo]

Rule of shunts, absolutely nothing apart from the shunt should be connected to the battery, including your starter battery negative.

sensor wires can be excluded like your smartguage and such.

Edited May 20, 2017 by Robbo

[rusty69]

It can go direct to the batteries, but more typically should go through the shunt. The only reason I can think you might want to go direct to the battery is due to lack of space on the shunt, in which case you could fit a busbar. 

[Robbo]

10 minutes ago, rusty69 said:

It can go direct to the batteries, but more typically should go through the shunt. The only reason I can think you might want to go direct to the battery is due to lack of space on the shunt, in which case you could fit a busbar. 

What's the point of the shunt if you're going by pass it and make what it displays totally inaccurate.

Edited May 20, 2017 by Robbo

[rusty69]

7 minutes ago, Robbo said:

What's the point of the shunt if you're going by pass it and make what it displays totally inaccurate.

So you can charge your batteries, if otherwise you couldn't fit another connection on the shunt. 

another reason, i suppose if you only wanted to measure loads only. 

Edited May 20, 2017 by rusty69

[Robbo]

18 minutes ago, rusty69 said:

So you can charge your batteries, if otherwise you couldn't fit another connection on the shunt. 

another reason, i suppose if you only wanted to measure loads only. 

You might as well just remove the BMV if your not going to wire it up right.  All of the functions will be incorrect apart from voltage, and it would make a rather expensive voltage gauge.  Even your loads only would be incorrect if your alternator/charger is on the other side.

[rusty69]

3 minutes ago, Robbo said:

You might as well just remove the BMV if your not going to wire it up right.  All of the functions will be incorrect apart from voltage, and it would make a rather expensive voltage gauge.  Even your loads only would be incorrect if your alternator/charger is on the other side.

Im not sure the load current measurement would be incorrect would it? 

 

The question asked by the OP was"whether the negative cable can go direct to the batteries "

 

Clearly the answer is yes. 

[WotEver]

9 minutes ago, Robbo said:

Even your loads only would be incorrect if your alternator/charger is on the other side.

What do you mean by 'other side'?  If all charging sources are connected to the battery directly and all loads connected via the shunt then the loads reading would be correct. 

[rusty69]

26 minutes ago, WotEver said:

What do you mean by 'other side'?  If all charging sources are connected to the battery directly and all loads connected via the shunt then the loads reading would be correct. 

I often wonder whether I should connect my solar direct to the battery so when the solar is on I can get a load only measurement on the BMV. 

Edited May 20, 2017 by rusty69

[nicknorman]

37 minutes ago, rusty69 said:

I often wonder whether I should connect my solar direct to the battery so when the solar is on I can get a load only measurement on the BMV. 

But then you can completely kiss you state of charge indication goodbye. If you aren't interested in your batteries' state of charge and just want to know the current going into the boat's services then fair enough. I think even the AH used value would stop working after a while - the AH used would continuously increase until the software or display gave up.

[rusty69]

23 minutes ago, nicknorman said:

But then you can completely kiss you state of charge indication goodbye. If you aren't interested in your batteries' state of charge and just want to know the current going into the boat's services then fair enough. I think even the AH used value would stop working after a while - the AH used would continuously increase until the software or display gave up.

True, but i tend to ignore the soc on the bm and use the sg anyway,cos I don't trust it. I also find it useful to know what load is on the battery, difficult to determine in the presence of solar. 

I suppose the answer is to add an ammeter to the solar, leave it all through the shunt and do a mental calculation if required. 

Edited May 20, 2017 by rusty69

[Robbo]

1 hour ago, WotEver said:

What do you mean by 'other side'?  If all charging sources are connected to the battery directly and all loads connected via the shunt then the loads reading would be correct. 

Yes but that would rewiring the alternator and other charging sources rather than just putting the solar on the battery.  Bit hard to do if you have a combi charger/inverter as well.

[WotEver]

3 hours ago, Robbo said:

Yes but that would rewiring the alternator and other charging sources rather than just putting the solar on the battery.  Bit hard to do if you have a combi charger/inverter as well.

I wasn't suggesting it as a 'good idea', I was simply asking what was meant by that phrase. 

[rusty69]

4 minutes ago, WotEver said:

I wasn't suggesting it as a 'good idea', I was simply asking what was meant by that phrase. 

Neither was I which was clear in my post.

I think the first reply kind of answered the question 

[Cloudinspector]

If I connect via the shunt is there a limit to how many connections can be fitted to a single post? There's already 2 connections on the load side of the shunt. 

[WotEver]

5 minutes ago, Cloudinspector said:

If I connect via the shunt is there a limit to how many connections can be fitted to a single post? There's already 2 connections on the load side of the shunt. 

There's no electrical limit. The limit is purely mechanical. If you can fit five terminals on a stud securely then you can have five connections. However, it is probably more practical (and better practice) to use a decent busbar once you get beyond 2 or 3. See the current thread about buzz bars [sic]. 

[Robbo]

If you have no room for a bus bar, you can get shunts that have more than one connection.  wouldnt be worth it for yourself.   When wiring up the one with the most load goes nearest to the shunt with the one with the least load at the top.

Edited May 21, 2017 by Robbo