measure amp usage - Page 2 - SailNet Community
Reply
 
LinkBack Thread Tools
post #11 of 18 Old 03-29-2010
A New Adventurer
 
funjohnson's Avatar
 
Join Date: Aug 2008
Location: Grand Rapids MI
Posts: 283
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 7
 
Keep in mind that you are charging via AC and that needs to be changed to DC. I would assume that there will be loss there just from the conversion via your charger. A multimeter is a low cost item that will be needed later on, and will give you a more accurate reading on your real 12v use.

1989 Sabre 34II Targa
mjsailing.com
funjohnson is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #12 of 18 Old 03-29-2010
Senior Member
 
Join Date: Aug 2006
Location: Arlington, VA
Posts: 1,853
Thanks: 0
Thanked 11 Times in 9 Posts
Rep Power: 10
   
Mick,

OK, let's talk about DC systems (battery powered systems), NOT about shore power. No spinning dials. DC meters don't work that way.

There are several ways to measure DC amperage draw. These include:

1. a simple multimeter placed in series with the power lead to a particular piece of gear; however, these can only be used up to about 10A maximum, i.e., for gear which doesn't draw much power.

2. a DC ammeter in-line with the power lead -- much like the old DC ammeters in cars and boats. Not a good solution.

3. a modern DC ammeter connected to a shunt, usually mounted in line with the negative or ground lead. These come in assorted sizes and can measure up to hundreds of amperes. So-called "battery monitors" fall into this category, but they have some additional capabilities which many boaters find useful.

4. a good clamp-on AC/DC ammeter. This is an excellent tool for most boat owners. A good one, like the Mastech 2138R, can be bought for about $100 and will pay for itself quickly in avoiding lost time, blind alleys, and big mistakes.

You can also draw up an energy budget using a pencil and paper, or a spreadsheet if you're computer-inclined. Most equipment is labeled with amperage draw, or it's wattage (which is easily converted to amperage). Once you have inventoried every electrical thing on board, you can figure out pretty easily how much power you draw in typical circumstances, and how much battery power you need (a minimum of twice the daily amp-hour draw). If, for example, you find that you use about 100AH per day, then you need a house battery bank of at least 200AH capacity. 300-400 would be better.

That then leads to the size of the battery charger. Typically, for flooded batteries you'd want a battery charger with about 20-25% of the capacity of your house battery bank. Say, a 25-30A charger for a 100AH battery bank.

The wiring size depends on the load to be put on each circuit, and how much voltage drop is permissible. For lights and other non-critical gear, a 10% voltage drop is acceptable. For more critical systems (like bilge pumps, frigs, radios, etc.) you'd want wiring which would have not more than a 3% drop. For charging wires from the battery charger and/or alternator, I'd go with even less voltage drop, i.e., larger wire sizes.

If all this sounds like Greek to you, it would be good to buy a book on basic marine electrical wiring (Charlie Wing's book is very good), and read it carefully. Then, before you get started with the rewiring project, get a qualified marine electrician -- preferably ABYC certified -- to have a look at your boat and/or your plan and finalize it. The $100-200 spent for such a professional look will save you lots of $$$, heartaches, and worse as you go forward with the rewiring project.

Bill

Last edited by btrayfors; 03-29-2010 at 01:46 PM.
btrayfors is offline  
Quote Quick Reply Share with Facebook
post #13 of 18 Old 03-29-2010
A New Adventurer
 
funjohnson's Avatar
 
Join Date: Aug 2008
Location: Grand Rapids MI
Posts: 283
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 7
 
Edit-Bill beat me to it with a much better explanation

1989 Sabre 34II Targa
mjsailing.com

Last edited by funjohnson; 03-29-2010 at 02:17 PM.
funjohnson is offline  
Quote Quick Reply Share with Facebook
post #14 of 18 Old 03-29-2010
Senior Member
 
Maine Sail's Avatar
 
Join Date: Jan 2003
Location: Maine Coast
Posts: 5,877
Thanks: 20
Thanked 219 Times in 167 Posts
Rep Power: 16
       
Quote:
Originally Posted by QuickMick View Post
I need to rewire the boat, and it has been widely (and wisely) advised that the first place to start is to figure out my consumption pattern. Is there an easy way to do this by using the demised electrical box on the dock? take a reading on a friday at 5, sunday at five, divide result by two (i thought a two day sample would be more accurate). anyone know 1)if this makes sense and 2)how the heck do i read an electric meter?

thanks
Please do not take this the wrong way as I mean it in sincerity and with the safety of you, your crew and your vessel in mind.

If you are asking this question, the way you are, you really should do a LOT more reading on the subject of re-wiring your boat.

We also don't know which consumption you are trying to ascertain? DC consumption? This is the wrong way to go about trying to figure it and one that is not likely to be accurate even if you do all the math including charge efficiency factors, inverter efficiency factors, charger / acceptance factors etc. etc. on and on.

Figuring "consumption" for 110v shore power is rather non-sensical as you size the wiring, over current protection and circuits based on loads. A 30 amp shore power system should be more than adequate for a G-30.

Charlie Wing and Nigel Calder's books are about the best going. I always recommend Charlie's book first as it is more simple and to the point and includes multiple wiring diagrams.

If you don't know how to figure basic consumption, re-wiring a whole boat could be a scary & unsafe process in the end result. Please, please, please educate yourself on marine AC/DC wiring before undertaking this project. Burn down a marina due to non-accepted wiring practices and your insurance company may not stand behind you.. Please be careful!

There are many ways to ascertain DC consumption but the most accurate, because many items are variable consumers, is a battery monitor.

You can also take a guess at hours/use/amps, based on rated amperage of an item, but in the case of a stereo, VHF, refridge, copmputers or other variable consuming items you will still likely have about a 10-15% variance from actual..

______
-Maine Sail / CS-36T


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.




© Images In Posts Property of Compass Marine Inc.


Maine Sail is offline  
Quote Quick Reply Share with Facebook
post #15 of 18 Old 03-29-2010
Telstar 28
 
sailingdog's Avatar
 
Join Date: Mar 2006
Location: New England
Posts: 43,290
Thanks: 0
Thanked 15 Times in 12 Posts
Rep Power: 14
         
That was my intent in another thread on solar power... as sizing a battery bank really requires you have some idea of what your daily usage is...

Then, if you are long term cruising, you multiply the daily usage by the number of days you want to go between recharging and then multiply that by THREE to get a rough bank size. This is based on the idea that you will generally not be recharging to 100% but to 85%, since it takes a lot more energy to go from 85% to 100%...

Then you try and size your passive recharging capacity to equal or be a bit more than your average daily usage.

Quote:
Originally Posted by btrayfors View Post
Uhhh....I think we have a disconnect here (pun intended).

Don't know what amp measurement of shorepower really has to do with rewiring the boat.

I suspect that whoever made the suggestion to "figure out my consumption pattern" was talking mostly about 12V DC power, i.e., power drawn from the batteries. That is very much related to boat wiring.

Am I right?

Bill

Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.
sailingdog is offline  
Quote Quick Reply Share with Facebook
post #16 of 18 Old 03-29-2010
Senior Member
 
Join Date: Jun 2006
Posts: 5,006
Thanks: 5
Thanked 18 Times in 18 Posts
Rep Power: 12
     
I assumed that the OP knew about DC amp measurements and was asking about shore power for a reason, am I wrong ?

What are you pretending not to know ?

Please support my
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
wind_magic is offline  
Quote Quick Reply Share with Facebook
post #17 of 18 Old 03-29-2010
Telstar 28
 
sailingdog's Avatar
 
Join Date: Mar 2006
Location: New England
Posts: 43,290
Thanks: 0
Thanked 15 Times in 12 Posts
Rep Power: 14
         
Probably.
Quote:
Originally Posted by wind_magic View Post
I assumed that the OP knew about DC amp measurements and was asking about shore power for a reason, am I wrong ?

Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.
sailingdog is offline  
Quote Quick Reply Share with Facebook
post #18 of 18 Old 03-31-2010
Don Radcliffe
 
Join Date: May 2007
Location: Santa Cruz
Posts: 396
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 9
 
I've been in marinas where I've had to pay for my electricity, and my estimate of liveaboard usage is 1-1.5 kwh/day. That is equivalent to 80-120 amp-hours at 12v, but it is hard to get an accurate estimate. The battery chargers are notoriously inefficient, I leave my solar panels connected, and we tend to leave things like the TV plugged in at the dock.
donradclife is offline  
Quote Quick Reply Share with Facebook
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
autopilot amp usage Brezzin Gear & Maintenance 4 01-02-2007 02:47 PM
VHF Radio: Usage and Etiquette Sue & Larry Learning to Sail Articles 0 05-14-1999 08:00 PM
VHF Radio: Usage and Etiquette Sue & Larry Seamanship Articles 0 05-14-1999 08:00 PM
VHF Radio: Usage and Etiquette Sue & Larry Gear and Maintenance Articles 0 05-14-1999 08:00 PM
VHF Radio: Usage and Etiquette Sue & Larry Her Sailnet Articles 0 05-14-1999 08:00 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome