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businessjett avatar image
businessjett asked

How to measure amp hours on my boat

I’ve read I need to go through my boat and 1 by 1 turn on all my stuff and measure it’s amp hours of each.


For example , fridge, toilet, anchor light, cockpit lights etc.


But I do I do this ? . Do I just have the fridge runnning and put the multi metre on the battery ? I read I might need to buy a multi metre with an amp clamp. But if I do what do I camp it onto ?

I plan to test the Amp hour of the fridge , then anchorage light, cabin lights, cockpit lights etc . 1 by 1


I’d like to do all these checks before I buy any of the Victron stuff to ensure I get all the right products

AGM Batteryamps
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Sarah avatar image
Sarah answered ·

Hi @businessjett, first thing you will need is a shunt. A multimeter on its own would be very limited. Unless you have a very large boat with large inverters the entry level 500 amp shunt will be appropriate. You can then go for either a standalone smart shunt with Bluetooth, BMV 712 which includes a shunt, or the Smart Shunt plus Cerbo GX. Each option will deal with the same amount of current - the difference is the connectivity options (VictronConnect via Bluetooth, the nice round screen on the 712, or the Rolls Royce Cerbo with touch screen and internet connectivity with VRM) and the budget. Either way the shunt gets wired in directly to the negative terminal in series with the boat load.

Sarah.

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businessjett avatar image businessjett commented ·
Thanks sarah . Yes it’s just 27ft. I will get the shunt and install it . Will that then tell me the amp hours ?
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kevgermany avatar image kevgermany ♦♦ businessjett commented ·
It's not quite that simple.

A BMV712 is a great thing to have, highly recommended. But it's an expensive way. And you need to disable ALL charging while you're taking the measurements. Amp hours are measured over time, so for decent numbers you need to think about how you will use the boat over the day/week. But it does record amp hours. It must also be installed correctly.

A simple current clamp simply clips around one wire going to the light/fridge etc. You will need to set to AC or DC. It measures amps. Be very careful with AC, there are often exposed live terminals when you take covers off to get to single cables.

Remember with amp hours that you take a reading with the appliance on, then estimate how long you'll use it during the day.

Also look at maximum current. What will the current be when everything is turned on at the same time? You probably think this won't be the case, but then someone leaves a heavy consumer on that you're not aware of and you plug in a kettle....

Personally I wouldn't measure. I'd simply calculate based on the rating for each appliance and how long it would be used each day.

At it's worst this exercise is guesswork. At best it's an estimate, so add a margin for safety. And if you're sizing batteries as well, think about how far you want to discharge them and how big a reserve you need between charges. This is especially important with lead based batteries.



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