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Bob Brugge Samba Member
Joined: April 09, 2015 Posts: 721 Location: Missoula, MT
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Posted: Sun Mar 10, 2019 11:20 am Post subject: Electrical math |
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Sorry in advance, math is not one of my strong suits.
I got the digital 6A. The destructions say you need at least 15 amp/hour for every half hour of operation. It also says it uses .9 amps for every 1k rpm. How can it be both?
My Bosch gennie looks like p/n GR15N found here: https://www.jbugs.com/product/GR15N.html which is a 30 amp gennie.
Not sure if it is or not, where is the p/n on the gennie? My bug is under about 2 feet of snow atm so looking is not really an option, at least till the snow melts.
So if this thing uses 15 amp/hour for every half hour of operation and I am on an hour long trip, something is going to get hot, I would assume. Does this mean on a 90 minute trip my car is going to die from lack of juice? I can just see me running down the road in the middle of the night with the radio blasting and the lights on and having it expire smack in the middle of no where...
Can someone help me make sense of these numbers? _________________ Keep on Dubbin'! |
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Dale M. Samba Member
Joined: April 12, 2006 Posts: 20365 Location: Just a tiny bit west of Yosemite Valley
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Posted: Sun Mar 10, 2019 11:57 am Post subject: Re: Electrical math |
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Not sure where the amp hour rate comes in but the MDS WTDN (Wiring Diagrams and Technical Notes) for Digital 6AL-2 (PN 6421) states it draws 0.7 amp per 1000 rpm... So if you are running down the road at 3500 RPM by the WTDN you are only going to draw 2.45 amps..... (0.7 X 3.5 = 2.45)
Dale _________________ “Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
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All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ... |
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Fred Winterburn Samba Member
Joined: April 17, 2013 Posts: 423 Location: Ripley Ontario Canada
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Posted: Sun Mar 10, 2019 1:29 pm Post subject: Re: Electrical math |
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Yeah, and the current rating will be based on an 8 cylinder, so about half of the current draw on a 4 cylinder for the same rpm. So in fact the MSD will use less current on average than the standard Kettering system. Fred
Dale M. wrote: |
Not sure where the amp hour rate comes in but the MDS WTDN (Wiring Diagrams and Technical Notes) for Digital 6AL-2 (PN 6421) states it draws 0.7 amp per 1000 rpm... So if you are running down the road at 3500 RPM by the WTDN you are only going to draw 2.45 amps..... (0.7 X 3.5 = 2.45)
Dale |
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Dale M. Samba Member
Joined: April 12, 2006 Posts: 20365 Location: Just a tiny bit west of Yosemite Valley
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Posted: Sun Mar 10, 2019 1:41 pm Post subject: Re: Electrical math |
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Fred Winterburn wrote: |
Yeah, and the current rating will be based on an 8 cylinder, so about half of the current draw on a 4 cylinder for the same rpm. So in fact the MSD will use less current on average than the standard Kettering system. Fred
Dale M. wrote: |
Not sure where the amp hour rate comes in but the MDS WTDN (Wiring Diagrams and Technical Notes) for Digital 6AL-2 (PN 6421) states it draws 0.7 amp per 1000 rpm... So if you are running down the road at 3500 RPM by the WTDN you are only going to draw 2.45 amps..... (0.7 X 3.5 = 2.45)
Dale |
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Fred:... Does the amp/hour rate mean anything to you?... Always though amp/hour was related to battery capacity, where watts per hour was total consumption for stated time frame...
Dale _________________ “Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ... |
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nsracing Samba Member
Joined: November 16, 2003 Posts: 9437 Location: NOVA
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Posted: Sun Mar 10, 2019 3:17 pm Post subject: Re: Electrical math |
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I am really understanding what you are asking here.
The generator has an output of 30 amps. YOur unit anly draws 6 amperes. The requirement for the line is at least 15 amperes. So what are you concerned about?
My point is - your only concern is to make sure the supply line has ample amperage or you will short it - overload!
If you have a 15 amp line and you stick a tool in it that draws 20 amps, hell ya you will blow a fuse or trip the breaker.
Did I make it worse? |
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runamoc Samba Member
Joined: June 19, 2006 Posts: 5593 Location: 37.5N 77.1W
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Posted: Wed Mar 13, 2019 7:45 am Post subject: Re: Electrical math |
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Quote: |
thing uses 15 amp/hour |
This is part of the 'formula' for the power company to charge you for electricity used. Say 15 amps @ 240 volts = 3600 watts. They will charge you 3.6 Kilowatts of electricity for 1 hour of consumption. 15 amps @120 volts = 1.8 Kilowatts. As for your self contained power generating equipment, time is not an issue. Amps on the other hand are. Fuses are sized to protect wires.
Your generator can produce 15 amps as long as the motor is running. _________________ Daily driver: '69 Baja owned 44 yrs - Plan B: '81 Rabbit Diesel LS Deluxe - Plan C: '72 Ghia
Yard Art: 2 Sandrails
Outback: '69 Ghia - '68,'69,'70,'72 Beetle - '84 Scirocco, GTI - Pair of '02 Golfs-
VW Wiring = It's just wires |
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Dan Ruddock Samba Member
Joined: October 25, 2012 Posts: 3574 Location: Sarasota, in my adopted state of Florida
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Posted: Wed Mar 13, 2019 8:25 am Post subject: Re: Electrical math |
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On your four cyl VW engine that will be .9 amps per 2k rpm as most MSD stuff has a 8 cyl mentality.
Dan |
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modok Samba Member
Joined: October 30, 2009 Posts: 26743 Location: Colorado Springs
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Posted: Wed Mar 13, 2019 4:45 pm Post subject: Re: Electrical math |
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The CDI box will draw less juice than the stock ignition system, no worries.
Take the instructions to mean they would like you to size the wires and battery as if it draws 15 amps, for your monster racing truck which does not have an alternator. |
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Fred Winterburn Samba Member
Joined: April 17, 2013 Posts: 423 Location: Ripley Ontario Canada
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Posted: Fri Mar 15, 2019 5:09 pm Post subject: Re: Electrical math |
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No,
All one needs is amps based on spark rate. Another useful but not so important amp rating is the amount of draw when the CDI is powered up but not delivering any spark. Some like the old Bosch 6 pin would draw 2 amps without doing any work. And then it would only draw another 1 amp from idle to the full spark rate. The MSD only draws a few milliamps when not doing any work, and then uses current as need be based on the spark rate as a function of rpm and also the multispark capability.
MSD should quote the current draw with reference to number of cylinders. I've never seen this spec that relates it to watts per hour. Energy consumption really only matters if running without an alternator. Maybe has some use for folks that run a race with only the battery and no alternator in the mix. Perhaps that is why they advertise it that way, Fred
Fred:... Does the amp/hour rate mean anything to you?... Always though amp/hour was related to battery capacity, where watts per hour was total consumption for stated time frame...
Dale[/quote] |
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mark tucker Samba Member
Joined: April 08, 2009 Posts: 23937 Location: SHALIMAR ,FLORIDA
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Posted: Sat Mar 16, 2019 12:50 pm Post subject: Re: Electrical math |
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and try to remember red+ black usually + smoke....and wore out shews. |
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EVfun Samba Member
Joined: April 01, 2012 Posts: 5446 Location: Seattle
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Posted: Sat Mar 16, 2019 1:06 pm Post subject: Re: Electrical math |
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Bob Brugge wrote: |
Sorry in advance, math is not one of my strong suits.
I got the digital 6A. The destructions say you need at least 15 amp/hour for every half hour of operation. It also says it uses .9 amps for every 1k rpm. How can it be both? |
33,000 rpm will do it.
On a more serious note, perhaps it means a 15 amp fuse is required? It may be that it draws 15 amps peak, but only for a small percentage of the time. Most of the time it draws almost nothing with a series of short quick bursts for coil charging. You need to fuse for the peak or the fuse may fail. _________________
Wildthings wrote: |
As a general rule, cheap parts are the most expensive parts you can buy. |
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Dale M. Samba Member
Joined: April 12, 2006 Posts: 20365 Location: Just a tiny bit west of Yosemite Valley
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Posted: Sat Mar 16, 2019 1:50 pm Post subject: Re: Electrical math |
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EVfun wrote: |
Bob Brugge wrote: |
Sorry in advance, math is not one of my strong suits.
I got the digital 6A. The destructions say you need at least 15 amp/hour for every half hour of operation. It also says it uses .9 amps for every 1k rpm. How can it be both? |
33,000 rpm will do it. :lol:
On a more serious note, perhaps it means a 15 amp fuse is required? It may be that it draws 15 amps peak, but only for a small percentage of the time. Most of the time it draws almost nothing with a series of short quick bursts for coil charging. You need to fuse for the peak or the fuse may fail. |
What fuse ?.... Where is it?.... Main power cables go directly to battery.....
https://www.jegs.com/InstallationInstructions/100/121/121-6425.pdf
Dale _________________ “Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ... |
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EVfun Samba Member
Joined: April 01, 2012 Posts: 5446 Location: Seattle
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Posted: Sat Mar 16, 2019 4:14 pm Post subject: Re: Electrical math |
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Even without a fuse, if the peak current is 15 amps it needs the wiring sized for 15 amps. If it is not the momentary voltage drop at full load will be undesirable. Capacitive loads can be brutal. It looks like they are just suggesting a battery sized large enough to handle these peak loads without excess sag. _________________
Wildthings wrote: |
As a general rule, cheap parts are the most expensive parts you can buy. |
Last edited by EVfun on Sun Mar 17, 2019 9:11 am; edited 1 time in total |
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HotStreetVw Samba Member
Joined: October 03, 2004 Posts: 871 Location: Wild West
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Posted: Sat Mar 16, 2019 4:24 pm Post subject: Re: Electrical math |
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I really struggled with the digital 6. I had a high RPM miss that kept me chasing my tail. Shielded cables, etc. failed attempt after failed attempt. I bought a 6-al2 and the miss was gone immediately. I know of several other racers with issues with the digital 6.
Also, MSD asks the end user to return defective units to them, instead send it back to the retailer. It’s a lot easier to have Jegs force the return with MSD since they buys 100Ks from them, rather than you deal with MSD. _________________ 4inBhore
50 Split - 2724cc NA. Haltech injected
62 Notchback - 2542cc Turbo WIP |
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Bob Brugge Samba Member
Joined: April 09, 2015 Posts: 721 Location: Missoula, MT
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Posted: Sat Apr 20, 2019 4:21 pm Post subject: Re: Electrical math |
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HotStreetVw wrote: |
I really struggled with the digital 6. I had a high RPM miss that kept me chasing my tail. Shielded cables, etc. failed attempt after failed attempt. I bought a 6-al2 and the miss was gone immediately. I know of several other racers with issues with the digital 6.
Also, MSD asks the end user to return defective units to them, instead send it back to the retailer. It’s a lot easier to have Jegs force the return with MSD since they buys 100Ks from them, rather than you deal with MSD. |
At what RPM did you have the miss? 3600 is as about as high as I turn it. I can return to the retailer as I work there, not a huge issue. I am going to instal this thing hopefully this weekend. Motor is out ATM till I get my carbs back so the wiring is wide open.
Not racing the bug all tho I would murder countless numbers to do so, just looking for the most efficient set up ever. _________________ Keep on Dubbin'! |
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King_vw61 Samba Member
Joined: February 03, 2018 Posts: 1383 Location: Southern California
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Posted: Sat Apr 20, 2019 6:28 pm Post subject: Re: Electrical math |
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i went from a old 7al to a 7alPlus and had to cross the green/purple wires from the crank trigger, ran like it had a rev limiter on, also had to re time it. It was 15 degrees once wires were swapped. It was at 30. 2 people have seen my car and asked if I figured out the wires needed to be crossed. MSD was no help at all. I even ran the shielded pick-up wires and re wired the coil so they were no where near each other.
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