How to measure electrical consumption

[Ex-SolentBoy]

With only that many items to check, why not first do the calculation theoretically. Look up the spec of the model on the Internet. The always list the power consumption. You can then make a calculation on how long you will use the item for.

Lights are easy, as you should know the bulb wattage anyway.

I know this is not a perfect solution, but in terms of telling you where your main problems lie, it is a very good start.

 

[ostell]

To measure at the breaker panel all you need to do is leave the item switched off and put the meter across the switch contacts, no disconnects.

Or disconnect one side of the battery and connect battery post to battery connector and switch items on and off.

Lights: probably max of 2 amps
VHF: less than 1 amp on standby, 6 amps on transmit
GPS less than 1 amp

The manuals should tell you the consumption.

Amps = watts/12

 

[Ru88ell]

I seriously doubt that. You might be able to, but I suspect it would take me half a week, and still look a bodge.

And unless they are filled with hydrogen, they weigh something. Adding weight that doesn't make the boat go faster is a no-no. An electrcian has - quite seriously - advised me to remove the clamps for the battery terminals, drill down into the terminals a bit, then tap them. Then screw a bolt into the terminals and attach everything to that. Just to remove the weight of the clamps (and he says it will also make a better electrical connection).

Maybe when I'm feeling a bit more courageous with my electrical skills.

I, too, was a complete electrical novice, but fitting a NASA BM1 compact was very easy. Wiring is colour coded, so even a child could do it. As for weight, well it weights practically nothing. It's a very light plastic box 124mm x 62mm x 23mm which can be fixed with double sided sticky pads or two screws. If you scrap the battery terminals as suggested you'll only need a screwdriver to install it.

If the tiny weight of this item is such a big thing, I trust you are on the diet from hell, have a shaved head, trim nose hair and clip big toe nails every other day.

 

[Rigger Mortice]

2x105 Ah batteries with a 1-2-both-off switch for powering the consumers. Charging is via a 25 watt solar panel and a fuel cell. Both have a 1-2-off selector, so I can run on one battery while charging the other, or (for example) leave one battery fully charged while I run on the other and also run the solar panel to it so it doesn't discharge so quickly (or at all during peak sun hours).

Unless I am missing something, I can't understand the advantage of working the batteries like that. In simple terms, one battery 100% charged and the other battery 80% charged will be no different from both batteries being 90% charged so, surely you may as well keep them both connected all the time?
I don't know how much power you get from a fuel cell, but a 25watt panel is not going to put a lot of power into the batteries; probably no more than around 20AH per day. Doubling up the batteries will have no affect, in the long run, on how much power you have available; you won't get more out than you put in.

You said earlier that weight was important to you. Perhaps you should consider getting rid of one of those batteries?

 

[ghostlymoron]

It looks as if I may not be able to go sailing tomorrow - pilot still in for repairs.

In case I can't go out, I'd like to use my time productively, and perhaps measure the electrical consumption of everything on the boat. That will help on longer trips, as I'd like to know what are the big consumers and shut them off if not necessary.

I have a multimeter, but how do I actually measure consumption? Where do I put the probes and what should I be measuring?

I really need an idiot's guide to doing this. Step by step. The only thing you can take for granted is that I can read English.

I think for your purposes a desktop investigation would be sufficient. Read the working current off each device (it should be marked next to the serial number) for lights the wattage will be marked on the bulb, devices that are not marked can be looked up on the net. As someone has already pointed out, starting currents are often several times higher than operating current so you'll have to make allowance for that.
As far as this exercise providing information to tell you what to turn off, do as I do, turn off anything you're not using at the time. For example only turn the water pump on when you are using water, turn off the saloon interior light when you are in the forecabin etc. Steering by hand saves power over autopilot (a lot if it's rough), you don't need the chartplotter on when you're away from the shore (perhaps put it on every hour or so to plot you current position. VHF - hmmmmmmmmmm should be on all the time really.
I don't see that knowing the current draw of something advises you whether it should be turned off - if its off, it isn't pulling down your battery.

 

[pelissima]

consumptions

In a similar day and mood last year, I first studied my cheap multimeter -something I advise- then, to avoid complications I took e achrespective fuse out and putting the probes at the contacts. You read directly consumption. Without extra care you will short the probes and blow either your multimeter or its fuse. To minimise this risk I would use one negative directly from batteries. By the way, your pilot is not as hungry as you think. Your fridge is.

 

[bbg]

If the tiny weight of this item is such a big thing, I trust you are on the diet from hell, have a shaved head, trim nose hair and clip big toe nails every other day.

You sound like my wife - especially the diet part.

Seriously, I have been able to remove about 15 kilos of stuff from the boat since I bought her. That has probably been more than offset by the stuff I've added, but everything I've added makes the boat go faster (or make it safer e.g. SeaMe), or is mandatory.

Rigger Mortice - the two batteries are mandatory under class rules.

 

[bbg]

Unless I am missing something, I can't understand the advantage of working the batteries like that. In simple terms, one battery 100% charged and the other battery 80% charged will be no different from both batteries being 90% charged so, surely you may as well keep them both connected all the time?

I haven't decided how I'm going to use the batteries. Maybe split, maybe together.
The only thing that worries me about using them together is if one fails it could bring down the other, and then I'd be in deep poo.

I think I'll do the desktop estimate for now.

 

[rob2]

I think you're right to do calculations based on the manufacturers' specs and your best estimate of the actual usage. A battery monitor, such as the Nasa, is still useful as it is monitoring in real time. After all, if your electrical consumption is giving cause for concern, you can usually switch off the fridge overnight and steer by hand as much as is practical.

It is commonly considered prudent to run on a single battery, the other being isolated and held in reserve. As said, should one battery develop a fault it can drain the other, good battery. In your case it sounds like the reserve can be recharged from the fuel cell whilst in isolation, allowing rotation of power sources.

Rob.