Simultaneous monitoring of battery discharge and charge

[stephen_h]

Apart from the expensive Victron displays is there a simpler way of seeing amp usage and charging simultaneously?
I have a Merlin smart meter that tells me the state of all four batteries - 2 x starter and 2 x domestic (linked).
I would like to see what various items such as fridge are drawing and how much solar/engine charging is going in.

 

[davidej]

NASA make a charge/ discharge meter for about £100 that also shows voltage and percentage charge in the battery.

 

[Andrew_Trayfoot]

Victron Smart Shunt is £85 and does much more than the NASA offering...
https://www.amazon.co.uk/Victron-En...t=&hvlocphy=1006680&hvtargid=pla-905632901260

 

[Sandy]

Do yo have any devices that display the solar/engine output?

 

[Refueler]

Apart from the expensive Victron displays is there a simpler way of seeing amp usage and charging simultaneously?
I have a Merlin smart meter that tells me the state of all four batteries - 2 x starter and 2 x domestic (linked).
I would like to see what various items such as fridge are drawing and how much solar/engine charging is going in.

The problem is you are wanting to see amps in and amps out as I understand it. If you are thinking you can do that at battery - then sorry - not possible as the displayed figure would be the net result of those two factors.
You would have to monitor at the units themselves to determine what they are putting out / drawing ...
If you have Solar - most controllers will show output of the panels through controller.

 

[Slowboat35]

Unsure of the concept of "amp usage" (sic) and charging as being seperate. The electrical consumers draw an many amps as they require, some for the fridge, some for the instruments, some for the autopilot and some for battery charging. The battery charger unit itself is not part of this when the engine is running, it only operates when connected to an external 220v power source. The batteries absorrb as much power as their internal resisitance allows or as much as is available after the demands of the others when fed 13.8v by the alternator
You probably could attach a shunt and meter to the battery cable to see what the bank is absorbing and do the same for the rest of the consumers but why would you want to do this? What useful info would it tell you? I can't imagine.

 

[B27]

You can put ammeters or hall-effect current sensors at various points in the circuit.
0.94€ 89% OFF|Halle Amperemeter Voltmeter DC 0 300V ± 50A 100A 200A 400A Batterie Monitor LED Digital Strom Spannung meter 12V 24V 36V 48V 60V AUTO| | - AliExpress

or there's these which will integrate current to tell you the charge:
Hall Effect Coulometer Digital Voltmeter Ammeter Energy Meter DC300V 100A 200A | eBay

There are other variations on the concepts.

 

[Minerva]

We have a generic £20 shunt on the battery betwixt the neg terminal and busbar wire;
https://amzn.eu/d/7zKTytS

That shows our consumption.

Your (well my at least) solar mppt charger has a Bluetooth app &/ display that shows the power produced and sent to batteries.

Good enough for our porpoises.

 

[PaulRainbow]

The problem is you are wanting to see amps in and amps out as I understand it. If you are thinking you can do that at battery - then sorry - not possible as the displayed figure would be the net result of those two factors.
You would have to monitor at the units themselves to determine what they are putting out / drawing ...
If you have Solar - most controllers will show output of the panels through controller.

This is the correct answer.

 

[William_H]

A DC clamp meter used on alternator output lead will show alternator charge. Move it to the load wires of all or specific loads to get that current. Move to solar charge wire to get solar charge current. This may satisfy your curiosity. Or if you want add hall effect current meters to all 3 for continuous readout. Get a cumulative amp meter if you want total information. ol'will

 

[michael_w]

Blue Seas digital ammeter. Simples.
Those battery 'fuel guage' are pretty inaccurate. Just keep a mental note of amps flowing in and out.

 

[Stemar]

I've ordered a couple of these, hoping that they'll do more or less what you want. You won't get the consumption of individual items, but I'm expecting to see amps going in and out, and the voltage, which will give me an idea of the state of charge.

DC 100V 50A 100A Digital Voltmeter Ammeter Dual LED display Volt Amp Meter Shunt | eBay.

I'll tell you in a few weeks if they're any good

 

[michael_w]

The shunts might not be man enough for engine starts. IRRC the Blue Sea ones are 100A

 

[stephen_h]

Victron Smart Shunt is £85 and does much more than the NASA offering...
https://www.amazon.co.uk/Victron-En...t=&hvlocphy=1006680&hvtargid=pla-905632901260

Thanks for all the suggestions.

One of my mppt's is Victron with bluetooth so I think the smart shunt is what I need.
May have to change the other mppt to bluetooth as well so all info is on my phone.

 

[Stemar]

The shunts might not be man enough for engine starts. IRRC the Blue Sea ones are 100A

I won't be putting the shunts where the starter current goes through them. I know that's a lot, but only for a few seconds, so not too important. I'm really only interested in the current on the domestic side. Keeping an eye on the voltage of the starter battery is nice, though I may decide only to use one on the domestic side, where amps dribble out constantly.

 

[VicS]

The shunts might not be man enough for engine starts. IRRC the Blue Sea ones are 100A

There are various shunts available from Blue sea from 50A to 500A but these current figures are for a calibration of 50mV potential difference not their max current carrying capacity.

It is recommended that the continuous rating is 2/3 these figures but their intermittent rating is 3x these for 3 seconds.

.

 

[B27]

I've ordered a couple of these, hoping that they'll do more or less what you want. You won't get the consumption of individual items, but I'm expecting to see amps going in and out, and the voltage, which will give me an idea of the state of charge.

DC 100V 50A 100A Digital Voltmeter Ammeter Dual LED display Volt Amp Meter Shunt | eBay.

I'll tell you in a few weeks if they're any good

I have some of those LED ammeter volt meter units, I use them for non-boat stuff.
They are fine for what they do, but they don't indicate negative current, so if you set them up to read the discharge, they will read zero if there's a net charge current going through them.
Also, the shunt is in the negative side. That's OK for e.g. measuring current from a solar panel, it just means the panel's -ve side is not the same as the boat's GND or Zero volts.
You can put one in line with your fridge for instance, but it means your fridge's -ve is not longer the same as other things on the boat.
Unless you know exactly how all the ground returns etc are configured o n your boat, it quickly becomes a limitation, in relation to the value of the information it gives.
Hence I take an interest in the Hall effect sensors and ammeter which can go in the positive side of circuits.

I've used a few isolated current sensors like this to mess around with Arduino current and charge monitors:
ACS712 Hall Board Current Sensor Module 5A /20A /30A -UK | eBay

But now I know roughly how the cookie crumbles, I just keep an eye on the volts and would turn the fridge of if I thought I needed to save power. The fridge will stay cool enough for another day.
I expect I will look at this a bit more if I think autumn is promising for sailing, with longer dark evenings and using the heater significantly.
Other priorities right now.

 

[rogerthebodger]

I have separate current shunts on the feed wired from mt solar panels going to my domestic batteries. I also have a hall effect shunt on the negative feed to my domestic battery thus displays both the input and output as + current or - current in or out.

My hall effect shunts will handle 600 Amps consumed by my bow thruster.

All you need to do is separate the wires charging the battery and the output wires and fit separate shunts into these 2 wires. I used to also have a wind generator with a separate shunt in the feed wire so I could monitor the current supplied by the wind generator

 

[KompetentKrew]

Thanks for all the suggestions.

One of my mppt's is Victron with bluetooth so I think the smart shunt is what I need.
May have to change the other mppt to bluetIf ooth as well so all info is on my phone.

Good idea.

You can "smart network" Victron Smart Solar controllers with the Smart Shunt - supposedly this makes solar charging more efficient, allowing the controller to account for any voltage loss between it and the batteries.