How do Atom Computer Ignition modules work?

[debe]

Ken W, give it a try as R1 is 1K in the Brown & Blue Atom modules, Ive also tried using 2 Zenner diodes 90v & 30V in series (120V) 5watt ones across C & E of a BD651. It still gives a sharp blue spark from crank upto 3000RPM on my test unit. CRO wave shows the Ign spike cliped at 120V protecting the BD651. The zenner diodes do get slightly warm, so don’t know about there long term reliability. Not sure where you guys bought your 2SD1071 transistors from but the 20 I purchased some time a go from China ive tested & all of them work fine.

[legendre]

Quick update, I’ve ordered a new batch of 10X 2SD1071L (apparently L = no lead, RoHS compliant) from a different eBay vendor. Price was a bit higher than the last batch (which was refunded by the previous seller).

We’ll see what shows up this time around..

[debe]

Well my 10, 2SD1071 transistors arrived today. On testing them I find 3 out of the 10 don’t work. The other 7 do work but not aswell as the the original ones I purchased 2 years ago. The diference in the 2 are the flywheel needs to turn a bit faster to get spark. I have also tested them on a Digitec component tester. It came up with some interesting data. Hfe will not be accurate due to B/E shunt resistor, this measures 1.5K ohms, also says there is a C/E protection diode. Hfe 5, Ic test 2.5Ma, B/E 1.12V, Test 4.18Ma. These are certainly very differen to the orig ones. The ones I purchased 2 years ago, Hfe 20597, Ic test 2.5Ma, B/E 1.22V, Test 4.18Ma. On these the tester didn’t say there was any resistor or int diode. And checking B/E there was no resistance reading. BUT these orig transistors work perfectly & you get a good spark just by flicking the flywheel over by hand. One wonders if some of the cheep Ebay ones are out of spec transistors being flogged off.

[legendre]

@debe

it appears that the 2SD1071 may be obsolete. Neither Digi-Key, Mouser nor Allied even recognize the part number. At this point, my thought is that we might consider evaluating potential replacements, such as the previously mentioned BU931 or ST901T.

Perhaps even the MJE13007A could be used, as the output device of a discrete Darlington pair with an appropriate low-power HV transistor on the driver side.

[debe]

Its certainly worth a try. I did do some tests on my dodgy ones & found the RPM when they reliably start is 700 RPM, were the others & the BD651 start at 300RPM. At this stage I have more than enough suitable transistors. Ive already spent more than enough money on Genuine Atom modules & pulling them apart to find the values at ($30 Aust each). Looking at the US patent 4,163,437, the gain of the switching is the important point.

[debe]

Did some tests on the 3 original Atom modules I dismantled switching transistors. Using a Digitec Component tester. All test as NPN darlington, & Hfe is not accurate due to B-E resistor of 2.2K, all have internal protection diode C-E. Two of the modules had a custom transistor marked A1, Hfe 8 Ic test 2.5Ma B-E 1V. Other one marked A2, Hfe 9 Ic test 2.5Ma B-E 1V.

[phil-b]

quote debe:

Did some tests on the 3 original Atom modules I dismantled switching transistors. Using a Digitec Component tester. All test as NPN darlington, & Hfe is not accurate due to B-E resistor of 2.2K, all have internal protection diode C-E. Two of the modules had a custom transistor marked A1, Hfe 8 Ic test 2.5Ma B-E 1V. Other one marked A2, Hfe 9 Ic test 2.5Ma B-E 1V.

I’d always assumed higher gain was needed. Here are some current "ignition darlingtons":

[legendre]

quote Phil B:

quote debe:

Did some tests on the 3 original Atom modules I dismantled switching transistors. Using a Digitec Component tester. All test as NPN darlington, & Hfe is not accurate due to B-E resistor of 2.2K, all have internal protection diode C-E. Two of the modules had a custom transistor marked A1, Hfe 8 Ic test 2.5Ma B-E 1V. Other one marked A2, Hfe 9 Ic test 2.5Ma B-E 1V.

I’d always assumed higher gain was needed.

It most definitely is an absolute requirement. The power NPN won’t turn-on soon enough with an hfe in the single or double digits, and this is very easy to demonstrate. Even the low hundreds is probably insufficient.

The hfe readings that debe posted are obviously incorrect, some sort of measurement artifact – possibly the result of an overflow error? The gain of a Darlington stage is: HFEd = (HFE1 * HFE2) + (HFE1 + HFE2) so it’s essentially impossible to have a Darlington with single-digit gain figures. Darlington gain is typically in the range of 500-2500 or better.

@debe

Would you have the time to make some manual bench measurements of gain in those Atom A1 and A2 parts? You know, just set up a variable PSU, a couple of ammeters and a resistor or two.. try a range of base currents from (perhaps) 1mA to 50mA, a total of ten points, and record the corresponding BE voltage, base current and emitter current.

Even if the supply is limited to 1A or 2A, that should give you a very solid picture of the current gain figures.

[ken-w]

My BU931T’s came in today, and I am a very happy camper. It fires a bright blue spark with no changes to debe’s design. Looks to be a good replacement for the 1071’s.

[legendre]

quote Ken W:

My BU931T’s came in today, and I am a very happy camper. It fires a bright blue spark with no changes to debe’s design. Looks to be a good replacement for the 1071’s.

Got one or two to share out? I’d like to experiment with this device..

PM on the way.

[Author]

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