pvb
Well-Known Member
But surely your alternator charges the domestic bank?
Volts but no amps?
- Thread starter BobnLesley
- Start date
But surely your alternator charges the domestic bank?
PaulRainbow
Well-Known Member
It does. But as i said, the windlass runs from the engine battery.
Connecting the engine negative to the shunt will mean the monitor sees the usage from the windlass and from the starter motor, this will be calculated as coming from the domestic bank as far as Ah used and SOC are concerned. The monitor will then see all of the alternator output and treat that as if it all went to the domestic bank, again, as far as Ah and SOC are concerned.
By not connecting the engine battery negative to the shunt the monitor does not see the power used by the starter or windlass. Granted, it also won't see what goes back in from the alternator, but that will be a small amount anyway, because of my solar panels.
It might be six of one and half a dozen of another, i might also be being a bit over fussy, but i think the errors in Ah used and SOC will be less with the engine battery negative not connected. It'll be different for others, who may have the windlass connected to the domestic bank or who do not have solar power. I can see what's happening with the alternator to a degree as i have an ammeter and the engine battery has its own voltmeter.
Either way, the fact that the OP does not see (and has never seen) the current from his alternator is likely because he also does not have the engine battery negative connected and it's all a red Herring with regards to his original post.
Heckler
Well-Known Member
Go back to my original, if the meter isnt showing amps going in, either wired incorrectly OR the shunt could be faulty, the guage depends on detecting voltage difference from either side of the shunt to show amps.
Stu
pvb
Well-Known Member
I'm afraid that's fundamentally wrong. The shunt, if correctly wired, will be the only thing connected to the domestic battery negative. The other side of the shunt will be connected to the boat's common negative. The shunt will only measure any current in or out of the domestic bank - it won't measure starting current out of the engine battery.
BobnLesley
Well-Known Member
PaulRainbow
Well-Known Member
Last edited:
pvb
Well-Known Member
I think you need to consider this a bit more. In particular, how does the alternator charge get into the domestic bank without being detected by the shunt?
PaulRainbow
Well-Known Member
Reading back, i misdescribed how mine is wired, i've edited it.
If i connect the engine negative to the shunt it measures the starter and windlass current, plus the alternator input. Leaving it off of the shunt it does neither. This is what i described in post #22.
pvb
Well-Known Member
OK, so you "misdescribed" your system. However, you haven't answered my question - how does the alternator charge current get into the domestic batteries without being detected by the shunt?
PaulRainbow
Well-Known Member
Because the engine negative is not connected to the shunt.
pvb
Well-Known Member
In normal systems, the shunt for the battery monitor is fitted in the negative lead of the domestic bank. On the battery side of the shunt, the only wire should go to the domestic battery negative pole, and no other wires should be connected to the domestic battery negative pole. In this way, the shunt will detect all the current either flowing in to, or flowing out of, the domestic bank.
The other side of the shunt would normally be connected to the boat's negative ground (usually the engine block). If it isn't, charging current couldn't reach the domestic bank from the alternator. Is that really how yours is wired??
PaulRainbow
Well-Known Member
No, as i keep saying. The engine is not connected to the shunt. If i connect the engine negative to the shunt how you describe the battery monitor measures starter and windlass current (as well as all alternator output).
My three domestic negatives and the engine battery negative are all connected together. The shunt is wired to the end domestic battery negative. The other side of the shunt is connected to all domestic inputs and outputs, therefore it measures everything into and out of the domestic bank, except the alternator.
The engine and windlass negatives are taken from the batteries. This way the monitor does not measure current going from the engine battery, back to the engine battery or any alternator output, because the alternator is wired to the engine battery. It charges the domestic bank via the VSR.
I realise this isn't the "normal" way to connect the shunt, but i don't want to be measuring the starter and windlass currents. It's worth remembering that i have solar panels and a dual sensing VSR.
BobnLesley
Well-Known Member
OK, so what have I learned/know new this morning: I have re-made and checked every connection from the display unit to the shunt/battery/ground and all appeared to be and remain sound - I got continuity all the way, on every cable; the only section not checked is from the unit itself, to the first chocolate-block connector (ours has two of those, no doubt made it earier to fit/wire on original installation. Also all cables/connections are unchanged from where they were connected for the six years we've owned the boat; all seemed good before, so nothing's changed since doing this - it still displays ampage going out, but not ampage coming in.
With regard to alternator ampage not and never having shown, I note that the one of the cables going from the shunt connects to a domestic battery negative post, precisely as shown on the NASA wiring diagram (our domestic battery bank shares a ground/earth cable and final connection with the start battery) whilst the other shunt cable, which nasa only note as connecting to 'load (neg)' runs to the earth bus-bar shared by most, but not all of the boat's electrical draws. I cannot see how re-locating that connection would help with this weeks problem, but I do wonder if it going to there is perhaps why the battery-monitor has never sensed the alternator's ampage input?
With regard to alternator ampage not and never having shown, I note that the one of the cables going from the shunt connects to a domestic battery negative post, precisely as shown on the NASA wiring diagram (our domestic battery bank shares a ground/earth cable and final connection with the start battery) whilst the other shunt cable, which nasa only note as connecting to 'load (neg)' runs to the earth bus-bar shared by most, but not all of the boat's electrical draws. I cannot see how re-locating that connection would help with this weeks problem, but I do wonder if it going to there is perhaps why the battery-monitor has never sensed the alternator's ampage input?
pvb
Well-Known Member
Ah, we're finally getting somewhere. You haven't wired your shunt in the normal way.
If you wired it in the normal way, your monitor would show alternator charge current. Indeed, there doesn't seem much point in having a monitor if it doesn't show all the charge current.
Here's a little diagram I did as a suggestion for another forumite. He was wanting to power his windlass from the domestic bank, so in this case the shunt would measure windlass current as well. But the shunt can't detect starting current.
PaulRainbow
Well-Known Member
Nope, been saying that since post #22, at least.
I'll have a move round of some wiring when i get a minute.
BobnLesley
Well-Known Member
Possibly an answer along with a further issue to resolve:
I now believe that my solar panels' MPPT controller is probably knackered - my fault, I thought it was rated for 25 amp maximum input, but on closer scrutiny, I find that it's only rated for fifteen and having fitted a third solar panel (215 watt total), I reckon at peak on a sunny day, I've probably been exceeding that - only by 10-15%, but that or something else seems to have been enough to kill it. So with a u/s solar charge controller, the amps that I've been stuffing into the batteries of late have been coming in at 19/20v.
So, does this get me any further forward in getting the battery monitor to display both in and outgoing amps, rather than only showing the output amps? As the solar panels' amps are coming into the battery bank at 19-20v, could it be that the monitor fails to sense/read them at that voltage, or is it more likely that this higher voltage has permanently knackered that element of the monitor?
In the short-term until I can get to somewhere with a solar controller for sale, I will continue to free-flow the solar panel input directly into the battery bank, whilst carefully monitoring the bank's temperatures and voltage (I've loads of distilled water to hand) as I can't see 15-20 amps going into a 450 amp/hr bank doing too much harm in the short-term, it might even clean some of the calcification off the plates? If the bank's voltage or temperature starts looking high I'll simply disconnect, similarly if we're both ashore together I'll shut it down. Any opinions about after dark; will any stored battery amps be lost into the no longer charging panels overnight?
I now believe that my solar panels' MPPT controller is probably knackered - my fault, I thought it was rated for 25 amp maximum input, but on closer scrutiny, I find that it's only rated for fifteen and having fitted a third solar panel (215 watt total), I reckon at peak on a sunny day, I've probably been exceeding that - only by 10-15%, but that or something else seems to have been enough to kill it. So with a u/s solar charge controller, the amps that I've been stuffing into the batteries of late have been coming in at 19/20v.
So, does this get me any further forward in getting the battery monitor to display both in and outgoing amps, rather than only showing the output amps? As the solar panels' amps are coming into the battery bank at 19-20v, could it be that the monitor fails to sense/read them at that voltage, or is it more likely that this higher voltage has permanently knackered that element of the monitor?
In the short-term until I can get to somewhere with a solar controller for sale, I will continue to free-flow the solar panel input directly into the battery bank, whilst carefully monitoring the bank's temperatures and voltage (I've loads of distilled water to hand) as I can't see 15-20 amps going into a 450 amp/hr bank doing too much harm in the short-term, it might even clean some of the calcification off the plates? If the bank's voltage or temperature starts looking high I'll simply disconnect, similarly if we're both ashore together I'll shut it down. Any opinions about after dark; will any stored battery amps be lost into the no longer charging panels overnight?
pvb
Well-Known Member
It's incorrectly wired.
BobnLesley
Well-Known Member
Insofar as having the monitor show the alternator's input, I suspect I ought to replace the shunt to bus-bar connection, with a shunt to engine casing connection to achieve that?
However, until yesterday morning the battery monitor has always displayed amps coming in and those going out and since yesterday morning it's shown only the amps going out. The wiring as it stands has not been changed in the last week/month/year, so your insistence that 'it's incorrectly wired' whilst no doubt true with regards to sensing alternator output, cannot possibly have any bearing on the immediate problem that I'm trying to address.
pvb
Well-Known Member
In which case see post 13.
PaulRainbow
Well-Known Member
Forrget about being incorrectly wired, as i keep saying, that and the failure to display alternator amperage is irrelevant to the current problem, that's a separate issue for another day, along with looking into my suggestion for better isolator switching and a dedicated starter battery.
The current problem is the lack of any reading of input from the solar controller. If the solar controller has failed in such a way that it is allowing the full output of 215w of solar panels to be fed to the batteries unchecked it will cause a lot more damage than a fried controller. I cannot see the batteries surviving such treatment, let alone electronics.
The current problem is the lack of any reading of input from the solar controller. If the solar controller has failed in such a way that it is allowing the full output of 215w of solar panels to be fed to the batteries unchecked it will cause a lot more damage than a fried controller. I cannot see the batteries surviving such treatment, let alone electronics.