Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 05-04-2018, 08:40   #1
Registered User
 
Macblaze's Avatar

Join Date: Nov 2013
Location: Edmonton/PNW
Boat: Hunter 386
Posts: 815
Inverter myths?

Ok, maybe they are not myths anywhere but in my head.

Our boat has a Magnum MS 2812 Pure Sine Inverter/Charger... 2800 watts.
I also have a small Motomaster Eliminator 300 W inverter (modified sine wave) that plugs into the 12v socket..

In my head it makes no sense to fire up the big inverter for no reason and I often just use the small one to charge up camera batteries etc. because it's more "efficient." But I looked at the specs today (yes, I want to be out sailing that bad...) and from what I can tell from all the gobbledygook is that the Magnum has an Inverter Efficiency (peak) of 89% and the specs on the Motomaster says Efficiency (maximum) 85%.

So that means I should just use the big one despite my inner prejudice that bigger must mean it uses more power?


The Magnum specs say:
No load (120 VAC output, typical) 30 watts
(that would be .25 a right?)

There is a spec on the Motomaster that says :
No load current draw (at 12V) <0.3 A

So... anyone care to check my math (and my assumptions)?
__________________

__________________
---
Gaudeamus igitur iuvenes dum sumus...
Macblaze is offline   Reply With Quote
Old 05-04-2018, 08:46   #2
Registered User

Join Date: Aug 2010
Posts: 1,146
Re: Inverter myths?

30 watts @ 120v = 0.25a

It looks like you mixing measurements. One is measuring Draw @ 12v, the other is measuring Output at 120V.
__________________

Shrew is offline   Reply With Quote
Old 05-04-2018, 08:46   #3
Registered User
 
Colin A's Avatar

Join Date: Mar 2013
Location: East of the river CT
Boat: Oday Mariner 19 , Four Winns Marquis 16 OB, Kingfisher III
Posts: 644
Send a message via Skype™ to Colin A
Re: Inverter myths?

Quote:
Originally Posted by Macblaze View Post
Ok, maybe they are not myths anywhere but in my head.

Our boat has a Magnum MS 2812 Pure Sine Inverter/Charger... 2800 watts.
I also have a small Motomaster Eliminator 300 W inverter (modified sine wave) that plugs into the 12v socket..

In my head it makes no sense to fire up the big inverter for no reason and I often just use the small one to charge up camera batteries etc. because it's more "efficient." But I looked at the specs today (yes, I want to be out sailing that bad...) and from what I can tell from all the gobbledygook is that the Magnum has an Inverter Efficiency (peak) of 89% and the specs on the Motomaster says Efficiency (maximum) 85%.

So that means I should just use the big one despite my inner prejudice that bigger must mean it uses more power?


The Magnum specs say:
No load (120 VAC output, typical) 30 watts
(that would be .25 a right?)

There is a spec on the Motomaster that says :
No load current draw (at 12V) <0.3 A

So... anyone care to check my math (and my assumptions)?
If it's 30W draw on the DC side (which is what I would assume) your original assumption would be correct. I have found it's usually better to have a small inveter for small loads and the big one for everything else. But there are alot of variables that can throw that off.
__________________
mysite: Colinism.com
Colin A is offline   Reply With Quote
Old 05-04-2018, 08:52   #4
Registered User
 
Kelkara's Avatar

Join Date: Oct 2016
Location: Vancouver Island
Boat: Hullmaster 27
Posts: 457
Re: Inverter myths?

I don't know anything about inverters ... but ...

for charging camera batteries, if it charges via USB, then you'll get way more efficiency by plugging a USB charger directly into the 12V without using an inverter to convert from DC to AC and back to DC again ... and if you forget to unplug it, the parasitic drain is probably less than 20mA.
Kelkara is online now   Reply With Quote
Old 05-04-2018, 08:52   #5
Registered User
 
Macblaze's Avatar

Join Date: Nov 2013
Location: Edmonton/PNW
Boat: Hunter 386
Posts: 815
Re: Inverter myths?

Quote:
Originally Posted by Shrew View Post
30 watts @ 120v = 0.25a

It looks like you mixing measurements. One is measuring Draw @ 12v, the other is measuring Output at 120V.
And...?

My understanding of the math is not up to understanding the implications.

Quote:
Originally Posted by Colin A View Post
If it's 30W draw on the DC side (which is what I would assume) your original assumption would be correct. I have found it's usually better to have a small inveter for small loads and the big one for everything else. But there are alot of variables that can throw that off.
But the specs imply otherwise don't they? .25 vs .3, 89% vs 85%

But I still want to believe you.



The specs imply the bigger unit is more efficient but...
__________________
---
Gaudeamus igitur iuvenes dum sumus...
Macblaze is offline   Reply With Quote
Old 05-04-2018, 09:18   #6
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jul 2005
Location: Bellingham
Boat: Outbound 44
Posts: 7,378
Re: Inverter myths?

Quote:
Originally Posted by Macblaze View Post
And...?

My understanding of the math is not up to understanding the implications.



But the specs imply otherwise don't they? .25 vs .3, 89% vs 85%

But I still want to believe you.



The specs imply the bigger unit is more efeinet but
Compare watts to watts, not amps. .3 amps at 12 volts is 3.6 watts. Much less than the 30 watts wasted with the larger inverter.
Paul L is online now   Reply With Quote
Old 05-04-2018, 09:23   #7
Registered User
 
Macblaze's Avatar

Join Date: Nov 2013
Location: Edmonton/PNW
Boat: Hunter 386
Posts: 815
Re: Inverter myths?

Quote:
Originally Posted by Paul L View Post
Compare watts to watts, not amps. .3 amps at 12 volts is 3.6 watts. Much less than the 30 watts wasted with the larger inverter.
Ohhhhhhh... Duh. We never talk watts when we are aboard so I was just comparing amps to amps.

Thanks.
__________________
---
Gaudeamus igitur iuvenes dum sumus...
Macblaze is offline   Reply With Quote
Old 05-04-2018, 09:30   #8
Are you serious?
 
sailorboy1's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: On the boat somewhere
Boat: Hunter 410
Posts: 15,362
Re: Inverter myths?

The efficiency matters what the load is. Doubtful that the big unit is 89% when running a small load

Using my little 400w inverter for charging phones etc and watch tv uses 2 amps less than if using my 2000e inverter. I care about amps not efficiency
__________________
jobless, houseless, clueless, living on a boat and cruising around somewhere
sailorboy1 is offline   Reply With Quote
Old 05-04-2018, 10:09   #9
Registered User
 
thomm225's Avatar

Join Date: Aug 2011
Location: Virginia Beach, VA
Boat: Bristol 27
Posts: 5,448
Re: Inverter myths?

Quote:
Originally Posted by Kelkara View Post
I don't know anything about inverters ... but ...

for charging camera batteries, if it charges via USB, then you'll get way more efficiency by plugging a USB charger directly into the 12V without using an inverter to convert from DC to AC and back to DC again ... and if you forget to unplug it, the parasitic drain is probably less than 20mA.
My $20.00 PWM Solar Controller has USB Ports also where you can charge camera batteries, phone batteries, lap tops etc

https://www.amazon.com/dp/B01MU0WMGT...a-584565296832

My 400 Watt Inverter does also but it's way better just to plug into the controller. My 1500 Watt inverter spare is still in the box
thomm225 is offline   Reply With Quote
Old 05-04-2018, 10:19   #10
Registered User
 
Macblaze's Avatar

Join Date: Nov 2013
Location: Edmonton/PNW
Boat: Hunter 386
Posts: 815
Re: Inverter myths?

Quote:
Originally Posted by sailorboy1 View Post
The efficiency matters what the load is. Doubtful that the big unit is 89% when running a small load

Using my little 400w inverter for charging phones etc and watch tv uses 2 amps less than if using my 2000e inverter. I care about amps not efficiency
Sometimes I think the manuals need manuals so you can interpret the numbers.

It makes sense that bigger loads would be more efficient on the bigger unit. I will just have to do some real time testing. Frankly, we hardly ever fire up the Magnum...it just feels like overkill, but it came with the boat and we are grateful to have it if we need it.
__________________
---
Gaudeamus igitur iuvenes dum sumus...
Macblaze is offline   Reply With Quote
Old 05-04-2018, 10:24   #11
Senior Cruiser
 
senormechanico's Avatar

Cruisers Forum Supporter

Join Date: Aug 2003
Boat: Dragonfly 1000 trimaran
Posts: 6,683
Re: Inverter myths?

Inverter efficiency curves generally show the best % around a 90% load.
30 watts at idle means at 12 volts input it's drawing around 2 1/2 amps from the battery.

Use a USB outlet for charging your camera etc. if you can.
__________________
One should try to "Die Young" as old as possible.
senormechanico is offline   Reply With Quote
Old 05-04-2018, 11:34   #12
Registered User

Join Date: Jan 2017
Posts: 11,761
Re: Inverter myths?

Yes, quality expensive ones are more efficient.

But the actual numbers vary amazingly, need a Watts Up to actually check your unique scenario.

If you really care, avoid using them, 90% of the load devices I see plugged into them come in DC versions, or are **actually DC internally**. Certainly anything with a battery is!
john61ct is online now   Reply With Quote
Old 05-04-2018, 11:50   #13
Are you serious?
 
sailorboy1's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: On the boat somewhere
Boat: Hunter 410
Posts: 15,362
Re: Inverter myths?

The problem with plugging DC devices that use AC and then convert them to DC is that lots of times they don’t like the way boats DC varies. On my boat the voltage of house battery varies between 12.1-14.9V. So don’t just think you can cut off the plug “brick” and connect directly to the batteries.
__________________
jobless, houseless, clueless, living on a boat and cruising around somewhere
sailorboy1 is offline   Reply With Quote
Old 05-04-2018, 11:53   #14
Registered User
 
Macblaze's Avatar

Join Date: Nov 2013
Location: Edmonton/PNW
Boat: Hunter 386
Posts: 815
Re: Inverter myths?

Quote:
Originally Posted by senormechanico View Post
Inverter efficiency curves generally show the best % around a 90% load.
30 watts at idle means at 12 volts input it's drawing around 2 1/2 amps from the battery.
This is what is frustrating about forums sometimes. Is this correct based on what I wrote or did you just read too quickly? This stuff confuses me enough as it is :-)

Quote:
Originally Posted by Macblaze View Post
The Magnum specs say:
No load (120 VAC output, typical) 30 watts
(that would be .25 A right?)

There is a spec on the Motomaster that says :
No load current draw (at 12V) <0.3 A
__________________
---
Gaudeamus igitur iuvenes dum sumus...
Macblaze is offline   Reply With Quote
Old 05-04-2018, 12:01   #15
Are you serious?
 
sailorboy1's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: On the boat somewhere
Boat: Hunter 410
Posts: 15,362
Re: Inverter myths?

30 watts divided by 12.5V DC is 2.4 amps. So if at 0 amps 120 volt AC uses 30w of power you are losing 2.4 amps DC to do nothing but be in standby waiting for an AC load. If you left that on all day that’s 57.6 amp-hours. That’s a lot of wasted power !!!!
__________________

__________________
jobless, houseless, clueless, living on a boat and cruising around somewhere
sailorboy1 is offline   Reply With Quote
Reply

Tags
inverter

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not 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 Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Watermaker Myths Kenomac Health, Safety & Related Gear 106 16-08-2016 17:33
Sea Myths and Sayings Mariners The Sailor's Confessional 5 29-09-2011 13:51
Cruiser Myths and Poopy-Copters svBeBe Our Community 9 13-06-2011 02:33
Mixing Metals Beneath the Waterline - Facts / Myths ? James Dieterich Plumbing Systems and Fixtures 28 08-11-2010 00:47
Calculating Amps Drawn Before Inverter and After Inverter ? impi Electrical: Batteries, Generators & Solar 23 26-09-2010 22:24



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 18:07.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.