Ammeter technical question

Thanks for useful info.
It is true that my question has nothing to do with monitors, I simply had no feel for what meters consume. After all, it would be nice to watch the solar power flowing in, but with a Briish summer and a 60watt panel wasting a quarter of an amp (3watt) would be too much, but a fraction of that would be acceptable. I think that I will fit one 5amp fsd meter for the pv and one 15amp fsd for the wind generator. Obviously it would be better to spend my time on the boat actually sailing, life does not always go according to the preferred plan.
 
john_morris_uk said:
I If 50mV across the shunt were equal to 50 amps (Not an unreasonable ball park figure for such a device) then the resistance is R=.05/50 =0.001 Ohms and the power loss though having the device in circuit when 50 amps are flowing though it will be 2.5 Watts
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Do not forget that Hall effect shunts drop no voltage, and cannot be overloaded, even engine starting, so fit on positive battery lead or on battery terminal.

Brian
 
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I replaced the 3 shunts on the negative side of both domestic and engine batteries with hall effect shunts from a well known supplier in Cornwall UK and they work very well.

I changed then due to the high volt drop when using my bow thruster and windlass.

Very happy and no connection with the supplier.
 
Here's an alternative that wont cost you any significant leccy. Carefully measure the resistance of the supply wire ( pos or neg doesnt matter) from the solar panel to the battery. Find some convenient points - for example my solar panel goes into a deck socket and then to the regulator so I would use the bit of wire from socket to regulator - its inside the boat, permanent etc.

Once you have that resistance then a simple calc based on Ohms law will allow you to draw up a graph equating the voltage drop along that wire with the current flowing through it. Wont take any significant extra leccy since you will be using that supply wire as your shunt.

Results wont be woldly accurate but then the info you get on momentary current is worth damn all. And you'll save yourself the cost of two ammeters.

No doubt some miserable sod will now come along with a fault in my scheme :D
 
pvb said:
Really? My common-or-garden 500A shunt only drops 50mV at 500A; doesn't seem very high to me.
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Mine droped 200mV at 200 Amp at I was feeding a 200mV DVM.

When I ran my bow thruster I was drawing over 500Amp so droping over half a volt just in the shunt.
 
No doubt some miserable sod will now come along with a fault in my scheme

Carefully measure the resistance of the supply wire ( pos or neg doesnt matter) from the solar panel to the battery
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How would one measure that resistance with a reasonable degree of accuracy and precision
The cable used will probably have a resistance of a few milli-ohms per metre ...1.0mm² for example is approx 0.017 ohms per metre
 
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If you are using a battery monitor to determine the state of charge you need to pass all the charging and discharging sources through a shunt.
An alternative is to run the bow thruster from the start battery. Most boats only monitor the AHrs in and out in the house battery bank so there is no need for a shunt.
 
VicS said:
How would one measure that resistance with a reasonable degree of accuracy and precision
The cable used will probably have a resistance of a few milli-ohms per metre ...1.0mm² for example is approx 0.017 ohms per metre
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Vic

I agree.

The bottom line is that using proper shunts in the circuits DOESN'T give you any significant losses. The losses are miniscule and can safely be ignored for all practical purposes.

If you have a bow thruster which takes 600 amps (thats 750 watts!!) then don't run that through the shunt - run it off its own battery or the engine start battery (which should be one that is designed for cold cranking amps.. and can take that sort of hammering.)

Its the domestic bank that most people want to monitor charge in and out of. Adding an ammeter into the circuit with a shunt (cheap) or a Hall effect device - slightly more expensive, but a good idea and a cunning plan) won't make any significant difference to the charge that is going into the batteries.
 
Rogershaw said:
I replaced the 3 shunts on the negative side of both domestic and engine batteries with hall effect shunts from a well known supplier in Cornwall UK and they work very well.

I changed then due to the high volt drop when using my bow thruster and windlass.

Very happy and no connection with the supplier.
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Re the good Hall Effect sensor supplier in Cornwall. Can you name him please?
 
I'm unclear on the whole concept.

So, you end up knowing what any given MOMENTARY input from your two sources may be.

But that doesn't help, 'cuz what you really want to know is the total amperage in over time.

So instead of buying two separate shunts and ammeters, why not get one battery monitor?

You can also use it to see the momentary input (say covering your solar to read the instantaneous from the other source, but you will get a wealth of more information.
 
The supplier of my bow thruster states 5.4 kW 7.3 HP.

But they also quote a figure of 580 Amp at 12VDC for max 3 mins.

I know 5.4 kW is only 450 Amp at 100 % efficient

Their 7kW is only available at 24 VDC

BTW my bow thruster can be powered from either of my domestic battery banks being 600 Ah each or my engine start battery.

The wiring is in fact 40mm by 20mm aluminium bus bars through very heavy duty switched.

AOWYN

Have a look at the web side in the post above my first post in this thread
 
Stu Jackson said:
I'm unclear on the whole concept.

So, you end up knowing what any given MOMENTARY input from your two sources may be.

But that doesn't help, 'cuz what you really want to know is the total amperage in over time.

So instead of buying two separate shunts and ammeters, why not get one battery monitor?

You can also use it to see the momentary input (say covering your solar to read the instantaneous from the other source, but you will get a wealth of more information.
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Find me a battery monitor that will allow me to read 3 battery banks. 3 separate solar panels and a wind generator. Plus I have 2 alternators on my main engine and a 50A mains battery charger which can feed each battery banks separately.

Sailing where I sail I want multi redundancy.
 
Many battery monitors will read 2 battery banks, typically a house bank and the voltage of a dedicated start battery. 3 banks is less common and less efficient as well. Anyone with 2 large house (domestic) banks would be better off to combine them as one bank twice the size. They will be drawn down less, will last longer, and will charge faster as well as their acceptance will be greater than a smaller bank. For a dedicated start battery that is seldom down more than 1 or 2 AH voltage is all that is necessary.
 
mitiempo said:
Many battery monitors will read 2 battery banks, typically a house bank and the voltage of a dedicated start battery. 3 banks is less common and less efficient as well. Anyone with 2 large house (domestic) banks would be better off to combine them as one bank twice the size. They will be drawn down less, will last longer, and will charge faster as well as their acceptance will be greater than a smaller bank. For a dedicated start battery that is seldom down more than 1 or 2 AH voltage is all that is necessary.
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True, but some people erroneously think they should have 2 domestic banks, alternate their use, and "rest" them.
 
2 separate house banks as well as a separate start battery makes a lot of sense for a long distance cruising boat.
The 2 house banks can easy be paralleled, but each can be monitored separately. It allows batteries of 2 different ages and even chemistries to used.
Good batteries are difficult to buy in remote parts of the world, shipping is expensive and may be very difficult due to the hazardous classification.
The versatility outweighs the slight extra cost IMHO.
 
Rogershaw said:
Find me a battery monitor that will allow me to read 3 battery banks. 3 separate solar panels and a wind generator. Plus I have 2 alternators on my main engine and a 50A mains battery charger which can feed each battery banks separately.

Sailing where I sail I want multi redundancy.
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What are you looking to monitor ?

Brian
 
Rogershaw said:
Find me a battery monitor that will allow me to read 3 battery banks. 3 separate solar panels and a wind generator. Plus I have 2 alternators on my main engine and a 50A mains battery charger which can feed each battery banks separately.

Sailing where I sail I want multi redundancy.
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Well, that helps, but doesn't answer my question. Why not get two battery monitors?

pvb said:
True, but some people erroneously think they should have 2 domestic banks, alternate their use, and "rest" them.
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I agree, erroneously is very well said. That is sooo 1970s. Brian's post is right, the largest house bank offers longer battery longevity.

noelex said:
2 separate house banks as well as a separate start battery makes a lot of sense for a long distance cruising boat.
The 2 house banks can easy be paralleled, but each can be monitored separately. It allows batteries of 2 different ages and even chemistries to used.
Good batteries are difficult to buy in remote parts of the world, shipping is expensive and may be very difficult due to the hazardous classification.
The versatility outweighs the slight extra cost IMHO.
Click to expand...

Your statement refutes itself. If separated for different ages and chemistries, then your second sentence says combine. I don't get the advantage, although I understand the "design" concept, but simply disagree.

A single larger house bank with a separate start (or reserve) bank is simple, extends battery life for the exact same amount of lead, reduces the number of potentially problematic connections (which are the weak link of any electrical system) and reduces the number of switches.

Going back to my original question: Why instantaneous ammeters instead of "over time" monitors? All battery monitors can read instantaneous amps in anyway.

That's all.
 
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