Ignition Current draw Calculations please

Jota Rob

Jota Rob

Hero member
Location
England
Ok, can someone help me with some figures please ?

I want to know, how much current draw Im likely to use based on the following assumptions.

Forget lights and starter motor. that means ignore everythng except current draw from ignition system.

Ignition system comprises, 1 x single ND Coil, 1 x Double ND coil, 1 x ignitec unit, 2 bosch pickup, although I dont think these take current but generate electrical pulses instead.

Assume an average of 6500 rpm for 15 minutes or 12 miles

Cheers Rob
 
I see where your heading with this! Can't give you any figures but I suspect that you will only need quite a small battery.

Loosing the starter and alternator is going to save quite a lot of weight  :)

James
 
Hi Rob - what we need here is someone who has made measurements of your setup.  I assume you want to size a battery for your ignition?  I believe the Ignitech allows you to control dwell setting which will have an impact on current draw. 

All I can offer is based on a DMC pulling ~50 watts at a nominal 14v - that's 3.6 amps. If you want to keep running for 15 minutes then in theory a 1AH battery would suffice.  However, that would not support the required discharge rate. You should also aim to discharge no more than 50% to retain some sort of economic battery life (lead acid type), not to mention reasonable terminal voltage.  Then there's self-discharge to think about.  Having a quick look at spec sheets suggests a 4AH is required - something like Yuasa YB4L.

HTH
 
When we were measuring stuff for Reds 320W alternators I measured the current draw from the ingnition out of interest, now it was a sasche unit, although I don't know what coils but it was only drawing about 1.5A even when revved up. It was certainly less than what I thought it would be. We recently put an Ignitech onto the Dyno but I didn't think to measure it but next time it is up and running I will do.

Can't help too much more than that except the current draw is only low so any half decent multimeter on the 10 amp scale will measure it easily. if you get it up and running yourself.
 
Well done, I found I've got a 10A scale on the multimeter so I'll do it this week and post up what I find, that'll give a difinitive answer, thanks for the help all...

Rob
 
Rob,

My mate Olivers' BMW that you've seen in Spa has an Ignitec, 1 stock Lav Bosch pick-up and 2 double Jap coils of approx 1.5 kOhm primary resistance firing his dual plugs with a wasted spark every revolution.  

Ignition draw is approx 0.7A at around 4-6000rpm.  A 5Ah battery is enough to get him through an entire Spa weekend without needing to recharge.

The Laverda BTZ ignition we rigged up for the bike before, drew almost 10 times that amount, needing a battery recharge after every turn!

piet
 
Hey Rob,

I've measured the Ignitech on my SFC and it pulls less than an amp (running one Dyna coil).  The small LiFePo4 batteries as used in RC helis etc are great.  I use this one:
http://epbuddy.com/index.php?main_page=product_info&cPath=22_7&products_id=21
This is based on the A123 cells, 4 in series to give 13.2V and 2.3Ah and weighs about 300g. Thus far it has been plenty for a couple of races/sessions in a row, with seemingly plenty of charge left when put on the charger.  You can get them in a block shape like this, or a flat pack configuration.
Given the weight of a triple you could go a bit more conservative and get the 8-cell version - still only ~600g - and you can probably run a whole day or even a meeting on it.
Note - you need the special balance charger to suit.

Cheers
Steve B
 
Morning...haha, you saw through my plans. Piet Fantastic, that's as close as you can get with the results, short of measuring mine....Steve, funny I wasn't going to post it but that's exactly where i was going.

Thanks again
 
Hi Rob,
Been running total loss for years on Monty,with the std iginition she was using just over one amp when the motor wasn't running,and just under one amp when running.
In theroy a battery say 10Ah should give you 1 amp per hour for 10 hours - thats the theroy but in practise it doesn't work out .
I current run a MOTOBATT battery of 5.5 Ah that last at least  a days racing.I re charge overnight for the following days activities,and carry a spare.Weight wise well around 2kg .
My advice would aim something around the 7/8 Ah size,check out the MOTOBATT website because they give you dimensions of the battery plus weight of.

Andy

 
Hi Andy, point taken on theory not being the same as reality.

Just for reference, the current draw test was quite intereting, Ammeter wired in series and swapped for main lead once motor running, I dont fancy testing my ammeter on the starter circuit.

Idle 800 rpm, current draw, 0.2 amp

Soon after, rises to around 0.9 - 1 amp, between 2 and 5 k revs
approx 6K = 1.3 amps, highest I saw was 1.4 amps and thats as high as I was prepared to rev it without load.

All the above runing motor with 12.44 volts showing at battery.

Rob
 
Hi Rob - Used to use a 7A/H battery on my racer - had a spare one that i used on the 2nd day if I couldn't trickle charge it overnight. Not oversure the weight benefit outweighs the convenience of a starter motor though !! - Regards - Phil
 
Hi Phil,
You have to look further down the line......no starter motor,dump alternator and starter clutch etc.Weight saving 4kg,ok 3.5. Also an extra .5bhp to the back wheel instead of being used to spin up alternator.More responsive thottle etc

Andy
 
Hi Andy - i think i would still prefer the convenience of the s/motor - have tried both ways - restarting a high comp triple on a wet grid on my own decided me  :D :D - Regards - Phil
 
Maybe ask the Kawasaki riders in SBK,there the only ones without and in the last submarine events in not so sunny England they were missed.Good to watch if its not been seen
 
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