How to test amp draw of everything connected to house battery

businessjett

businessjett

Member
Jun 10, 2021
79
Mooloolaba Sunshine Coast Qld Australia
Boat Info
2004 SeaRay 275 ( 260DA in USA )
#USSERR7124K304

5.0 Mercruiser Bravo 3 leg
Engines
2004 5.0 Mercruiser with Bravo 3
Serial No OM684005
Hello

I bought a multi metre and googled how to measure the amp draw from each device. Eg the fridge .

They seem to suggest I need to remove the fuse for the fridge and connect my positive and negative to each side so the multi metre becomes part of the circuit . But I have no idea where the fuse is ?

Would I get the same result if I did this at the battery ? By just putting the multi metre on the terminals.

it’s been suggested I 1 by 1 measure everything. Fridge, radio, lights , water pumps , so I know how big my new lithium house battery needs to be for it to last a few nights out.


I have tried to use the search feature but not very good with it
 
The "fuse" is actually the breaker that's in the MDP.

For a comparison... I ran 3 days on a group 27 DC battery (lead acid) as a "trial" - same boat (US version, of course) as you. Throughout those three days, the engine was run for maybe an hour total. Fridge ran the whole time... lights as needed and some stereo... anchor light (LED) overnight... and of course water pump and Vacuflush. It even started the engine on the last day.
 
If you're just looking to estimate your current load for the new battery, you should be able to garner that from the manuals for those devices, and/or straight from the placards on them. You sure can use an ammeter to determine the current draw, but keep in mind that most multimeters can't handle more than 10 amps. Compressor devices (A/C, refrigerators), can demand a pretty hefty surge current to start, then drop down quite a bit once running. That surge would most likely blow the fuse in your meter.
 
do you not have an amp meter on your DC and AC panel? You should be able to add one load at a time and see the needle climb with each load.
 
If testing individual pieces of equipment, if anything draws more than 10 amps, per manual, don't use the DVM or Multimeter, as they blow the internal 10A fuse.

Use a clamp on ammeter (good ones do AC and DC), which most better ones have leads and can also be used as a a DVM
 
An Amp meter will have some limit in the amount of current it can handle before it becomes your fuse, and blows. To measure from the battery, you are best off installing a shunt which effectively "shunts" a small but fixed proportion of the current to your meter. From there it is just a simple math exercise to calculate the actual current draw. This is how most battery monitors work.
 
As mentioned above, you should already have a current meter in you panel. But that meter is only going to give you a rough reading. You really need to plan for the max loads, that will be labeled on each appliance. The best way to get an idea of the individual loads is to use a correct current meter, and you digital meter is not that in this case. You need to use one with an inline shunt with a meter. If you don't want to put in a permanent one then this could be connected temporarily to get your readings. But if your going to get a lithium battery you will need something like this mounted in you panel permanently.
 
Just a side note... he has a small DA - they don't have a amp meter - only a voltmeter in the panel.
 
ttmott said:
10 amps in almost all meters.
Click to expand...

I was referencing a stand alone shunt that could handle above 100 amps. Inductive DC current monitoring is not as accurate as using a shunt in DC in my experience. But agree that 10A is not enough in a hand held meter.
 
SKybolt said:
I was referencing a stand alone shunt that could handle above 100 amps. Inductive DC current monitoring is not as accurate as using a shunt in DC in my experience. But agree that 10A is not enough in a hand held meter.
Click to expand...
Of course - probably my mistake assuming they were talking about hand held meters.
 
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