Solar panels, battery monitors, and bafflement

[BlueStringPudding]

I am confused by the readings on my battery monitor, more so than usual since I wired in my latest solar panel last night. It would be great if you guys could help unpick this for me, if indeed it needs unpicking. I have a theory of my own (towards the bottom of this post) which may or may not be correct.

 

I have a Mastervolt BTM battery monitor which I think (think) is wired in correctly. There's another thread about that elsewhere.

 

Scenario 1

Some time after running the engine last night:

No solar panels wired in:

Battery monitor shows Domestic batteries 100% at 12.7v

Battery monitor shows 0A current draw on the batteries (probably correct, all equipment except it and the MPPT was turned off)

Battery monitor shows 0A current charge going in to the batteries (correct)

Starter 13.35v (high... But maybe not lost that "just charged enthusiasm" yet)

 

Scenario 2

8am this morning, 12 hours after last charging the batteries from the engine and having watched a few hours of tele last night:

Not fully tested yet 240w panel now wired in to the domestic bank (MPPT led indicates PV charging): Battery monitor shows Domestic batteries: 93% at 12.41v (probably about right)

Battery monitor shows 0A current draw on the batteries (probably correct, all equipment except it and the MPPT was turned off)

Battery monitor shows 0A current charge going into the batteries (contradicting MPPT indicator light)

Fully tested and well used 50w solar array attached to the start battery: battery monitor shows Starter 13.35v ( high voltage implying charging or sumit wrong with battery or incorrect monitor, battery monitor doesn't show any current going in though, despite the fact that small solar array usually produces 0.2A - 3.0A)

 

Scenario 3

When I came home from work about 7.30pm this evening, now having not run the engine for 24 hours:

Not fully tested yet 240w panel still wired in to the domestic bank (MPPT led indicates PV charging, voltage at PV end 48.6v): battery monitor showed Domestic batteries: 100% at 12.69v

Battery monitor shows 0A current draw on the batteries (probably correct, all equipment except it and the MPPT was turned off)

Battery monitor shows 0A current charge going into the batteries (contradicting MPPT indicator light) and contradicting PV voltage although PV current not measured, there may be a fault with the PV)

Fully tested 50w solar array attached to the start battery: Starter 13.31v (again battery monitor doesn't show any charge going in which is likely to be incorrect)

 

I have the stereo turned on now and a light on, and the battery monitor shows -1.0A which is about right. It also does show current going in when the engine is running, although I've no idea how accurate its measuring of that is.

 

I'm confused! I could understand if my new PV panel wasn't working properly or I'd not wired in properly, but the fact that the battery monitor showed the domestic voltage rising from 12.41v to 12.69v while i was at work today, and the fact the MPPT PV charging led is lit (until the sun sets then it goes out), and the PV panel itself is showing a voltage if 48.6v on an overcast evening (highest I've measured on a sunnier day is 53v) - all those things point to a working solar panel.

 

The smaller 50w array has worked for a couple of years so I have no reason to assume its not working now. But I DID change something when tidying up the wiring recently.under the advice of people on this forum, I changed the 50w solar array negative from the hull earth to the battery negative terminal. Similarly the new PV panel negative it to battery negative not hull earth. The hull earth, again for reasons best known to the previous owner appears to be connected to or actually simply is the shunt for the battery monitor. So I suspect those negatives are now the wrong side of the shunt for the monitor to be able to read. This is my theory and may be utter bunkum.

 

If I move both solar panel negatives back to the hull earth, the monitor may be able to read it again. (i dont know without testing, perhaps I've missed something else) BUT! I'll be back in a situation where if the isolator switch (which is in the negative) is stitched off, everything gets earthed through the skinny solar cables, which isn't overly safe.

 

I have a new isolator switch for the positive side, however I am trying to source the fat cables with lugs pre-attached that I need before I can wire it in. In the meantime, do I:

1. 
    
   
2. Leave the set up as is, and accept I won't be able to see the charge from the solar panels with the monitor till they are earthed to the hull, which I won't do till I have the new positive isolator switch in place
   
3. Move the solar negatives back to the hull earth and just don't turn off the present isolator switch, (which sits in the negative)
   
4. Disconnect my solar panels until I can install the positive isolator switch (warning, that will make me rather grumpy coz I'm excited about them)
   
5. (I'm not giving the option of bypassing the isolator switch by connecting the negatives as I won't be able to isolate anything for now)
   
6. Any other option I've not thought of, in case there's a new safety issue I've made myself vulnerable to
   
7. Do something to the shunt / hull negative (BSS passed with present electrical set up, I hasten to add)
   

Edited June 29, 2012 by BlueStringPudding

[Chris Pink]

I haven't read everything but it sounds like your solar controller negative might be wired to the battery side of the monitor shunt

 

"This is my theory and may be utter bunkum."

 

Just read this it's not bunkum (what a delicious word)

 

I still haven't grasped your system.

 

your battery negative should be connected to your hull (and/or engine) connection and your shunt nothing else.

 

Every other negative should be connected the other side (upstream) of the shunt

[BlueStringPudding]

Thanks, Chris. I'll try to explain how the shunt appears (inherited where it currently is, from the previous boat owner) I may be able to take a photo of it tomorrow.

 

The shunt looks like two heavy duty bolts with nuts attached to them., with two tiny screws to the side. The whole shunt itself is attached to the hull. I cannot tell whether th back of the shunt is isolated from the metal hull or not.

 

The top large bolt has a big fat negative cable attached to it, coming from the batteries I assume (sorry it's dark now so I can't check). The bottom large bolt has loads of negative cables attached to it, fat and thin so is presumably the hulll earth connection (could well be wrong. The gearbox is the earth for the starter motor amd presumably the alternators, but not much else it seems). This bottom large bolt on the shunt is where the negative cable from the small 50w solar array used to be attached, and from there the battery monitor was able to read its charge.

 

The isolator switch , which is in the negative cabling, is between the battery bank and one of the shunt large bolts. (this is why I was wondering whether the shunt was behaving as the hull earth point)?

 

The two small side screws on the shunt have battery monitor wires attached to them only.

Edited June 29, 2012 by BlueStringPudding

[Chris Pink]

Sounds about right, the solar negative should go back to the bottom bolt.

 

I am assuming that the shunt is isolated from the hull in some way - it must be or you wouldn't get any reading, in or out

 

It's unlikely to be the hull bonding point though i suppose it could be if one side was isolated and one wasn't.

 

That wouldn't be very good practice though, really you should have a clear and separate hull bonding point.

 

The small screws on the shunt should go to the battery monitor but this is only for wiring convenience.

 

And the isolator is between the top shunt connection and the battery negative.

 

If your monitor doesn't show a large engine start current then there will be a connection between the top bolt and your engine. This should really not be through the hull but should be an earth strap from engine to batteries.

 

I think that's about it.

Edited June 29, 2012 by Chris Pink

[BlueStringPudding]

Thanks, Chris. The monitor shows a large starter motor draw but never seems to show a particularly high domestic alternator current. Maybe that's correct, and really is the alternator's output, or maybe it isn't. (tends to show 4A-15A or so, for a 70A alternator). Batteries are pretty new though and not too molested by my power usage yet!

[BlueStringPudding]

Sounds about right, the solar negative should go back to the bottom bolt.

 

 

 

If I take the negative from the 50w solar array off the starter neg and back to the bottom bolt, and take the MPPT negative off the busbar which is connected to the domestic battery neg, and move that to the bottom bolt, that will sort it? It'll smeg up my nice tidy busbar wiring though Simply passing all the negs on the busbar (including bilge pump etc) straight onto the shunt?

 

If the bottom bolt of the shunt was the hull earth, that would bipass the isolator switch.

Edited June 29, 2012 by BlueStringPudding

[kathleen bridget]

I am suprised that your batteries are showing 100% when at 12.7V., mine sit at 12.86 ish when fully charged.

 

Did you get the MT5 remote panel for the Tracer unit, would be interesting to compare the V readings on that as opposed to the Mastervolt

I am suprised also that it is not showing the domestics over 13V at 7.30pm, it doesn't appear to be giving you what it should.

 

by the way, this is mathleen not kathy

Edited June 29, 2012 by kathleen bridget

[BlueStringPudding]

I am suprised that your batteries are showing 100% when at 12.7V., mine sit at 12.86 ish when fully charged.

 

Did you get the MT5 remote panel for the Tracer unit, would be interesting to compare the V readings on that as opposed to the Mastervolt

I am suprised also that it is not showing the domestics over 13V at 7.30pm, it doesn't appear to be giving you what it should.

 

by the way, this is mathleen not kathy

 

I thought that was an unconventional post for Kathy!

 

No I didn't buy the extra meter for the MPPT, seemed like a waste of money when I already have a battery monitor installed. The voltage at the solar panel itself was 48v this evening which I checked with a multimeter.

 

Like I said above, I don't know if there is just an issue with my battery monitor wiring, or also with the new PV panel (possible), or also the wiring between the PV panel and the MPPT. I notice that the PV Charging green led on the MPPT although lit is a fraction fainter than the green led showing battery status. I wonder if that's normal or might indicate a weak connection on the PV wiring?

 

If I wake up early enough in the morning (banter to travel to later) I'll shove my multmeter pokey things* into the screw terminals of the MPPT to see if I can get a voltage reading there, and how it compares to the voltage PV end of the cabling.

 

* stop me if I get too technical for you

Edited June 29, 2012 by BlueStringPudding

[kathleen bridget]

 

Like I said above, I don't know if there is just an issue with my battery monitor wiring, or also with the new PV panel (possible), or also the wiring between the PV panel and the MPPT. I notice that the PV Charging green led on the MPPT although lit is a fraction fainter than the green led showing battery status. I wonder if that's normal or might indicate a weak connection on the PV wiring?

 

The MPPT green light will start to fade as the sun drops down, it eventually pops off just after sunset.

[BlueStringPudding]

Ok. I have yet to see it in daytime bright sunlight as I only finished wiring it in properly last night and I worked all day today. I'll look at it tomorrow.

Edited June 29, 2012 by BlueStringPudding

[RLWP]

Bet it isn't charging much right now

 

Richard

[BlueStringPudding]

 

Can't tell, me battery monitor wiring is iffy

[Grace and Favour]

Bet it isn't charging much right now

 

Richard

 

What about BSP's natural glow?

[BlueStringPudding]

unprovoked flattery will get you everywhere. Greenie time

[Chris Pink]

If I take the negative from the 50w solar array off the starter neg and back to the bottom bolt, and take the MPPT negative off the busbar which is connected to the domestic battery neg, and move that to the bottom bolt, that will sort it? It'll smeg up my nice tidy busbar wiring though Simply passing all the negs on the busbar (including bilge pump etc) straight onto the shunt?

 

If the bottom bolt of the shunt was the hull earth, that would bipass the isolator switch.

 

When you say 'busbar" do you mean this connects the battery negatives together?

 

if so the only thing that should connect to that is the shunt top bolt ( via the isolator) and battery negative terminals

 

All other negatives should connect to the shunt bottom bolt (make another busbar?)

 

Your engine starter negative connects to here too so your hull bond should also connect at this point

 

ps when I 'connect' I mean electrically which might not be the same as physically (as in smiletpete's advice to connect your new solar to your inverter)

 

Sounds like the 50W solar is already in the right place electrically.

 

if it was me I'd want to know what isolates the shunt from the hull (but as it seems to be working ok it's not crucial)

[Gibbo]

BSP

 

I don't think you've given enough information to be certain of this but I think your shunt is wired incorrectly (from reading between the lines).

 

All the domestic bank negatives should be connected together, then all connected to the battery side of the shunt. There should be nothing else connected here (which I think is what you have... so far, in the main). But the engine start battery negative should be connected to the other side of the shunt, not the same side as the domestic negatives.

 

Your monitor will not (and should not) show any current into or out of the engine start battery, which yours does, which is why I think it's wired up wrong.

 

With it wired as it is, it doesn't stand a chance of monitoring the domestics properly.

 

Connecting your solar panels to the battery negatives, instead of the other side of the shunt, is definitely why they're not showing on the monitor.

 

I know it's in the pipeline, but you really do need to get rid of that negative isolator and replace it with two in the battery positives. The problems negative battery isolators can cause are many and horrendous.

 

The small screws on the shunt should go to the battery monitor but this is only for wiring convenience.

 

This is wrong. It isn't "only for wiring convenience."

[BlueStringPudding]

BSP

 

I don't think you've given enough information to be certain of this but I think your shunt is wired incorrectly (from reading between the lines).

 

All the domestic bank negatives should be connected together, then all connected to the battery side of the shunt. There should be nothing else connected here (which I think is what you have... so far, in the main). But the engine start battery negative should be connected to the other side of the shunt, not the same side as the domestic negatives. The starter battery negative is connected in series to the domestic negatives, which in turn go through the isolator to the shunt. I appreciate you're saying that's wrong.

 

Your monitor will not (and should not) show any current into or out of the engine start battery, which yours does, which is why I think it's wired up wrong.

 

With it wired as it is, it doesn't stand a chance of monitoring the domestics properly.

 

Connecting your solar panels to the battery negatives, instead of the other side of the shunt, is definitely why they're not showing on the monitor? Okay, thanks for clarifying .

 

I know it's in the pipeline, but you really do need to get rid of that negative isolator and replace it with two in the battery positives. The problems negative battery isolators can cause are many and horrendous.

 

 

 

This is wrong. It isn't "only for wiring convenience."

Edited June 30, 2012 by BlueStringPudding

[Gibbo]

"The starter battery negative is connected in series to the domestic negatives, which in turn go through the isolator to the shunt."

 

This is wrong. It cannot work properly wired up like that.

 

The engine start battery negative should be connected to the load side of the shunt. The battery monitor will then not show any engine start battery currents (in or out) but it will be able to correctly measure the domestic battery currents.

 

PS. You're boat is not alone in this. Almost nobody seems capable of wiring a shunt up properly. Hence this...

 

 

Has been up on the website for years and gets thrown out again every couple of months because, yet again, a shunt is wired incorrectly.

Edited June 30, 2012 by Gibbo

[BlueStringPudding]

When you say 'busbar" do you mean this connects the battery negatives together? Yes

 

if so the only thing that should connect to that is the shunt top bolt ( via the isolator) and battery negative terminals It does connect to the battery negative, then through the isolator to the shunt. I'll need to check which shunt bolt in a moment.

 

All other negatives should connect to the shunt bottom bolt (make another busbar?)

 

Your engine starter negative connects to here too so your hull bond should also connect at this point .

 

ps when I 'connect' I mean electrically which might not be the same as physically (as in smiletpete's advice to connect your new solar to your inverter)

 

Sounds like the 50W solar is already in the right place electrically. The 50w solar is directly connected across the starter battery. Technically it shares the same negative as everything else at the moment because the starter battery negative is wired in series with the domestics, through the negative isolator. If I understand Gibbo correctly, the starter battery will need a different negative to hull connection once the isolator switch is changed. Which will mean the 50w solar array negative will no longer be wired in series with the domestic bank.

 

if it was me I'd want to know what isolates the shunt from the hull (but as it seems to be working ok it's not crucial)

 

"The starter battery negative is connected in series to the domestic negatives, which in turn go through the isolator to the shunt."

 

This is wrong. It cannot work properly wired up like that.

 

The engine start battery negative should be connected to the load side of the shunt. The battery monitor will then not show any engine start battery currents (in or out) but it will be able to correctly measure the domestic battery currents.

 

PS. You're boat is not alone in this. Almost nobody seems capable of wiring a shunt up properly. Hence this...

 

 

Has been up on the website for years and gets thrown out again every couple of months because, yet again, a shunt is wired incorrectly.

 

Thanks Gibbo. Are you telling me this wring diagram IS how to do it. Or is WRONG? Can't quite tell from your wording. It looks right to me.

 

Interesting that my current wiring set up will be what gives me confused readings from the battery monitor. I've often wondered wheterh it's trying to average out the voltage between the starter and the domestics rather than accurately measuring one or the other. The monitor always does show a is offering starter reading to the domestics reading, but not always what I'd expect.

 

Thanks.

Edited June 30, 2012 by BlueStringPudding

[David Mack]

 

Has been up on the website for years and gets thrown out again every couple of months because, yet again, a shunt is wired incorrectly.

 

And the batteries??

[Gibbo]

Thanks Gibbo. Are you telling me this wring diagram IS how to do it. Or is WRONG? Can't quite tell from your wording. It looks right to me.

 

The diagram is correct as it is. The words show you what you shouldn't do. Yours isn't wired like the diagram. You have your engine start battery negative connected to the other side of the shunt.

 

Interesting that my current wiring set up will be what gives me confused readings from the battery monitor. I've often wondered wheterh it's trying to average out the voltage between the starter and the domestics rather than accurately measuring one or the other. The monitor always does show a is offering starter reading to the domestics reading, but not always what I'd expect.

 

It's measuring the current into and out of each battery, but it has no way of knowing which battery it's going into or out of. It can only monitor one battery for state of charge. So when you charge into your start battery, it thinks that is going into the domestic battery.

 

And the batteries??

 

?

[David Mack]

 

?

 

And the (domestic) batteries are wired incorrectly in that diagram, at least according to some bloke called Gibbo...

[Gibbo]

And the (domestic) batteries are wired incorrectly in that diagram, at least according to some bloke called Gibbo...

 

Ahh right. It's not my diagram. Someone uploaded it with the engine battery on the other side of the shunt to show what he had in his boat. I moved that link to where it should be and reposted it. We were discussing shunts so the other bit got left.

[Bob-18]

Looking at the DOMESTIC battery.

The positive wires go off the the things they do already, via fuses, switches etc. No change.

 

ONE connection only, and ONE, only to the negative terminal

This connection goes to one side of the shunt.

And on the other side of the shunt you have all the negative ("earth") returns from all the domestic kit.

A connection to the negative terminal of the "start" battery

A connection to the hull.

 

 

 

(Obviously if you have some sort of BATTERY voltage monitor on the domestic battery that will be connected to the domestic battery positive and negative terminals directly - remember shunts work by "dropping" a tiny voltage across them, and the magnitude of this voltage varies with the current passing through the shunt...)

[BlueStringPudding]

Gibbo, please excuse the quick adaptation of your diagram but this appears to be the present set up. It's not difficult t see how to get from this set up to the one above.

 

 

I checked the top bolt of the shunt, only the negative from the isolator switch is connected to that. All other negatives are connected to the other side of the shunt

Edited June 30, 2012 by BlueStringPudding