Reply
 
Thread Tools Search this Thread Display Modes
 
Old 02-02-2008, 09:23 AM   #1
Rivet Master
 
davidz71's Avatar
 
1986 25' Sovereign
Southern Middle , Tennessee
Join Date: Mar 2002
Posts: 3,150
Images: 23
Current draw question

I have a question for the electrical wizzards on the forum. I found the following formulas for watts, volts, amps regarding current draw:

watts= volts X amps

amps= watts
volts

While researching led replacement bulbs for replacing my 1141 bulbs in selected fixtures and in lieu of my 3 flourescent fixtures, I have seen some flourescent fixtures with two 8 watt bulbs (16 watts) rated at 1.3 amps draw and others rated at 1.5 and 1.6 amps. According to the formula above it should be 1.33 amps (they must have rounded down) but why the 1.5 and 1.6 amp figures? Could this be a typo, the result of less efficient ballast for the higher rated amp fixtures or the bulbs themselves? Are these formulas set in stone or is there a fudge factor involved? My inquiring mind wants to know.

As an afterthought, I have also seen the 1141 bulb 18.4 watt bulb rated at 1.44 amp draw and 2.1 amp draw which is what the 1156 26.9 watt bulb is rated for. Is this just lack of attention to detail in the printing of this information?
__________________

__________________
Craig

AIR #0078
'01 2500hd ext. cab, 8.1 litre gas, 5 sp. Allison auto
3.73 rear end
Mag-Hytec rear diff cover
Amsoil Dual by-pass oil filtration system
Amsoil synthetics all around
265 watt AM Solar, Inc. system
davidz71 is offline   Reply With Quote
Old 02-02-2008, 10:49 AM   #2
2 Rivet Member
 
nangoff's Avatar
 
2004 28' International CCD
Franklin , Tennessee
Join Date: Oct 2003
Posts: 93
Craig, I'd buy a couple and series them up with a ammeter and see what you get. Don't know exactly but possibly the assembly could pull higher wattage till the components warm up so the vendor has to put the higher ratings on to size supporting equipment (fuses, wire, etc.) GG
__________________

__________________
nangoff is offline   Reply With Quote
Old 02-02-2008, 10:50 AM   #3
Rivet Master
 
Excella CM's Avatar
 
1978 31' Excella 500
Venice , California
Join Date: May 2006
Posts: 1,061
Use this: W = IxIxR
__________________
"Not all who are laundering are washed" say Bill & Heidi

'78 Excella 500,"The Silver Pullit". vacuum over hydraulic disc brakes, center bath, rear twin. '67 Travelall 1200 B 4X4 WBCCI 3737
Excella CM is offline   Reply With Quote
Old 02-02-2008, 11:05 AM   #4
2 Rivet Member
 
nangoff's Avatar
 
2004 28' International CCD
Franklin , Tennessee
Join Date: Oct 2003
Posts: 93
W=IxIxR is the same as current times volts. Also, "R" is very difficult to measure while under load so that's why most folks use IxE.
__________________
nangoff is offline   Reply With Quote
Old 02-03-2008, 09:35 AM   #5
Rivet Master
 
Join Date: Dec 2002
Posts: 1,313
Images: 4
Craig, the equations are accurate. The 1.33 amps is the theoretical current when 12 volts is applied to a 16 watt resistor. However, the voltage from a charged "12 volt" battery is way over 12 volts. Ohm's Law tells us that for a given resistance, current is proportional to the applied voltage. The resistance in this case is 12 volts divided by 1.33 amps, which equals 9 ohms. As a charged 12 volt battery will be at about 12.7 volts, the current will increase to 12.7 volts divided by 9 ohms, equals 1.4 amps. I suspect that some manufacturers are rating the bulbs for the real world of RVs, where 12 = more than 12! That enables RV manufacturers to rate their wiring and breakers for the higher current. Just a guess on my part. Nick.
__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
nickcrowhurst is offline   Reply With Quote
Old 02-03-2008, 11:25 AM   #6
Rivet Master
 
davidz71's Avatar
 
1986 25' Sovereign
Southern Middle , Tennessee
Join Date: Mar 2002
Posts: 3,150
Images: 23
Thanks Nick. I hadn't thought about the fact that my battery when fully charged is more like 12.7 volts.
__________________
Craig

AIR #0078
'01 2500hd ext. cab, 8.1 litre gas, 5 sp. Allison auto
3.73 rear end
Mag-Hytec rear diff cover
Amsoil Dual by-pass oil filtration system
Amsoil synthetics all around
265 watt AM Solar, Inc. system
davidz71 is offline   Reply With Quote
Old 02-03-2008, 01:09 PM   #7
Retired Moderator
 
john hd's Avatar
 
1992 29' Excella
madison , Wisconsin
Join Date: Aug 2002
Posts: 4,644
Images: 40
craig

also keep in mind most auto bulbs are really 14 volt when comparing wattage.

they are just called 12 volt to not cornfuse people.

john
__________________
you call them ferrets, i call them weasels.
john hd is offline   Reply With Quote
Old 02-03-2008, 09:37 PM   #8
Rivet Master
 
davidz71's Avatar
 
1986 25' Sovereign
Southern Middle , Tennessee
Join Date: Mar 2002
Posts: 3,150
Images: 23
Quote:
Originally Posted by john hd
craig

also keep in mind most auto bulbs are really 14 volt when comparing wattage.

they are just called 12 volt to not cornfuse people.

john
Hi John,
That also makes sense because the alternator guage on my t2500hd is always showing over 14 volts even though I know they aren't the most accurate things. Well, I do know that I am using less current from the leds and that is what I was after. One more fixture with dual 48 SMT leds and I'm through replacing 1141 bulbs.
__________________
Craig

AIR #0078
'01 2500hd ext. cab, 8.1 litre gas, 5 sp. Allison auto
3.73 rear end
Mag-Hytec rear diff cover
Amsoil Dual by-pass oil filtration system
Amsoil synthetics all around
265 watt AM Solar, Inc. system
davidz71 is offline   Reply With Quote
Old 02-03-2008, 09:56 PM   #9
2 Rivet Member
 
nangoff's Avatar
 
2004 28' International CCD
Franklin , Tennessee
Join Date: Oct 2003
Posts: 93
Craig, It would be good to find out, if you can, what the maximum ambient temperature the LED's can operate at. LED's are skiddish on elevated temperatures, they don't like it...so before you invest a lot of money on them its best to find out all of their charactoristics; trailers can get hot some times and when you turn the LED's on while hot they may fail. Making matters worst they don't like elevated voltages either (increases operating temperature), therefore some include voltage regulators to thwart this.

Gerry
__________________
nangoff is offline   Reply With Quote
Old 02-03-2008, 11:57 PM   #10
Site Team
 
, Minnesota
Join Date: Aug 2003
Posts: 6,940
Images: 59
I think the difference in amp draw may be due to differences in the type of driver used to power the lamps. If the lamps use a high efficiency push-pull transistor inverter, the power draw would be the lower rated 1.3 amps; if a transformer style ballast is used, it would dissipate the extra 2 watts as heat, and those two watts would increase the amp draw to 1.6 amps.

So I'm backing your "less efficient ballast" theory.
__________________
markdoane is offline   Reply With Quote
Old 02-04-2008, 07:18 PM   #11
Retired Moderator
 
john hd's Avatar
 
1992 29' Excella
madison , Wisconsin
Join Date: Aug 2002
Posts: 4,644
Images: 40
Quote:
Originally Posted by davidz71
Hi John,
That also makes sense because the alternator guage on my t2500hd is always showing over 14 volts even though I know they aren't the most accurate things. Well, I do know that I am using less current from the leds and that is what I was after. One more fixture with dual 48 SMT leds and I'm through replacing 1141 bulbs.
craig,

you would have some fun up here in the great white north! there are mornings when i leave for work with 2 batteries that are around -10 degrees i get voltage readings upwards of 15 volts!

when they warm up a bit under the hood they drop down about a volt or so. don't under estimate the voltmeters on the newer trucks, i have checked mine against my simpson and a el cheapo DMM and the one in the truck is prety close.

any work with batteries as far as voltage and current must be compensated for tempature.

this will give you a chuckle if you are into old school electric theory. also from a wisconsinite!

Automotive Ignition Systems - Google Book Search

john
__________________
you call them ferrets, i call them weasels.
john hd is offline   Reply With Quote
Old 02-04-2008, 08:46 PM   #12
Rivet Master
 
davidz71's Avatar
 
1986 25' Sovereign
Southern Middle , Tennessee
Join Date: Mar 2002
Posts: 3,150
Images: 23
John,
I scrolled through the first 20 pages of the link to the book and thought about my first year of engineering at Vanderbilt. Now I remember why I got out of engineering.
__________________
Craig

AIR #0078
'01 2500hd ext. cab, 8.1 litre gas, 5 sp. Allison auto
3.73 rear end
Mag-Hytec rear diff cover
Amsoil Dual by-pass oil filtration system
Amsoil synthetics all around
265 watt AM Solar, Inc. system
davidz71 is offline   Reply With Quote
Old 02-04-2008, 08:49 PM   #13
Rivet Master
 
davidz71's Avatar
 
1986 25' Sovereign
Southern Middle , Tennessee
Join Date: Mar 2002
Posts: 3,150
Images: 23
Quote:
Originally Posted by nangoff
Craig, It would be good to find out, if you can, what the maximum ambient temperature the LED's can operate at. LED's are skiddish on elevated temperatures, they don't like it...so before you invest a lot of money on them its best to find out all of their charactoristics; trailers can get hot some times and when you turn the LED's on while hot they may fail. Making matters worst they don't like elevated voltages either (increases operating temperature), therefore some include voltage regulators to thwart this.

Gerry
Gerry,
I have 5 led bulbs of various type now. I'm going to watch them carefully as to the amount of time I run them and general temperature. The one over the stove will stay on more than any of the others so it will get the real workout.
__________________

__________________
Craig

AIR #0078
'01 2500hd ext. cab, 8.1 litre gas, 5 sp. Allison auto
3.73 rear end
Mag-Hytec rear diff cover
Amsoil Dual by-pass oil filtration system
Amsoil synthetics all around
265 watt AM Solar, Inc. system
davidz71 is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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
Current Airstream Merchandise msterry Commercial Listings 12 02-06-2008 01:44 PM
Where Do You Draw The Line? rseagle Community Polls 34 10-13-2006 07:57 PM
Corel draw x3 Devoman Off Topic Forum 0 07-06-2006 08:20 PM
How much power should it draw? 26.982 amu Electrical - Systems, Generators, Batteries & Solar 7 04-16-2006 10:09 PM
A/C Current Draw Pick Furnaces, Heaters, Fireplaces & Air Conditioning 6 07-03-2003 08:36 PM


Virginia Campgrounds

Reviews provided by




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 06:41 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.

Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.