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Bob Brugge
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PostPosted: Sun Mar 10, 2019 11:20 am    Post subject: Electrical math Reply with quote

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?
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Dale M.
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PostPosted: Sun Mar 10, 2019 11:57 am    Post subject: Re: Electrical math Reply with quote

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 Winterburn
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PostPosted: Sun Mar 10, 2019 1:29 pm    Post subject: Re: Electrical math Reply with quote

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.
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PostPosted: Sun Mar 10, 2019 1:41 pm    Post subject: Re: Electrical math Reply with quote

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


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
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nsracing
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PostPosted: Sun Mar 10, 2019 3:17 pm    Post subject: Re: Electrical math Reply with quote

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? Very Happy
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PostPosted: Wed Mar 13, 2019 7:45 am    Post subject: Re: Electrical math Reply with quote

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.
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Dan Ruddock
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PostPosted: Wed Mar 13, 2019 8:25 am    Post subject: Re: Electrical math Reply with quote

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
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PostPosted: Wed Mar 13, 2019 4:45 pm    Post subject: Re: Electrical math Reply with quote

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
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PostPosted: Fri Mar 15, 2019 5:09 pm    Post subject: Re: Electrical math Reply with quote

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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PostPosted: Sat Mar 16, 2019 12:50 pm    Post subject: Re: Electrical math Reply with quote

and try to remember red+ black usually + smoke....and wore out shews.
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EVfun
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PostPosted: Sat Mar 16, 2019 1:06 pm    Post subject: Re: Electrical math Reply with quote

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. Laughing

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.
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Dale M.
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PostPosted: Sat Mar 16, 2019 1:50 pm    Post subject: Re: Electrical math Reply with quote

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
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PostPosted: Sat Mar 16, 2019 4:14 pm    Post subject: Re: Electrical math Reply with quote

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.
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Last edited by EVfun on Sun Mar 17, 2019 9:11 am; edited 1 time in total
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HotStreetVw
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PostPosted: Sat Mar 16, 2019 4:24 pm    Post subject: Re: Electrical math Reply with quote

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.
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Bob Brugge
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PostPosted: Sat Apr 20, 2019 4:21 pm    Post subject: Re: Electrical math Reply with quote

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.
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PostPosted: Sat Apr 20, 2019 6:28 pm    Post subject: Re: Electrical math Reply with quote

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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