'Overloading' shunt and battery monitor

[LittleSister]

I would like to fit a battery monitor - nothing fancy, just to keep track of battery charge/discharge. Money is tight. I have available such a monitor (Blue Sea, if I remember correctly - can't lay my hands on the documentation just now) and shunt. The shunt is rated at 200 amps.

Most of my loads are modest (a few lights, a few instruments, small fridge, small diesel blown air heater, small domestic water pump, etc.), but I've had a bow thruster fitted of 'nominal' current draw of 315A and recommended fuse of ANL 250, i.e. higher than the 200A rating of the shunt. (In a previous thread it was said that such motors have very high initial momentary current draw then it drops, but I don't know whether that is true or by how much it drops.)

1) If I put this in the monitored circuit will it fry the shunt, or fry or confuse the battery monitor?

2) If I run the bow thruster separately (i.e. bypassing the shunt), will this render the battery monitor readings completely meaningless most/all of the time, bearing in mind that I don't anticipate using the bow thruster often, and very rarely for more than a few seconds? (He said tempting fate!)

 

[rogerthebodger]

I had a similar issue as my bow thruster was rates at 600 Amps.

I replaces my shunt with a hall effect sensor to reduce the overload and volt drop

Got mine from Halcyon of this parish from the UK

 

[William_H]

It is doubtful if the shunt itself a resistor would be overloaded as in smoking hot. Usually a big lump of resistor. At 20mv and 200 amps power dissipation would be 4watts. Almost nothing. Double the current and so volt drop you get 16w which might raise the temperature a bit. Now what your monitor would do with a double normal max voltage in (ie 40mv) is a good question. Perhaps to destroy but certainly not likely to register the current. ol'will

 

[Caladh]

Why put the bow thruster thru the shunt? You know it’ll gun the batteries for less than a minute. You know it’ll take a chunk of amps while you run it. I'm assuming you’d run it with the engine running. You battery monitor will show the alternator chucking in some amps after you‘ve used the bow thruster….. so go with your option 2.

 

[simonfraser]

are you sure the bow thruster is going through the shunt ?
mine has a battery up front to take the initial load

 

[Neeves]

Don't you also have a windlass?

Jonathan