Magneto Magnet Strength

[groily]

Some pix I took earlier are virtually identical to yours LJ!  I shan't redo them at lower resolution to get under the threshhold here.
As to 'Why mess about with compasses?', well, just a Q of trying to get a handle on things as useful reference points for 'the next time', and simply of knowing more. Curiosity is good, even if it killed a proverbial cat or two.
As Beezermacc rightly says and MG said earlier, Ks (and MO1 magdynos and most things Lucas with those same materials in) retain their oomph well, but I have seen quite recently one K series with no discernible magnetic pull at all. It certainly wouldn't - couldn't - be made to work as it was.
Remagnetising is a service most of the professional rebuilders seem to offer, so presumably there is some history/need - and of course the Lucas service sheets covered it too in some detail (see eg http://www.brightsparkmagnetos.com/library/LWImags/Remagnetisation%20of%20magnetos,%20Sec%20D-6,%20Issue%202.pdf).

[RichardL]

Ken, Groily and, yes, all you poo-pooers,

Just to see how my mag compares with the examples given, and to make some people crazy, I've executed the experiment with the compass. My needle deflection is 41 degrees. However, the earth's magnetic field strength where I am is 54.4 mTesla. With no other way I could figure to draw a comparison between this and the 48.6 mTesla at Hampshire, I just applied a linear factor and come up with a virtual 46 degrees deflection. Hmmm? Not knowing exactly what to make of this, I am sending you my magneto case so you can do the test there. Naaaaah! Anyway, unless someone screams otherwise, I think I'll put it back together with the new Brightspark and the existing coil and magnet. I think I'll know right away if the spark is stronger, and disassembly, if needed, is not a big problem.

Just in case, any suggestions where to get magnetized (so many joke lines here) around Chicago, or in the U.S., for that matter.

Richard L.

[KenF]

Ummm, Richard ... I stand to be corrected, but the following makes sense to me at least ...

What's making your compass needle point North-South is the component of the Earth's magnetic field in the horizontal plane, so you need to multiply by the cosine of the dip angle. So for you in Chicago, it's 54 cos 72 = about 16.7 uT. For me in Hampshire, it's 48 cos 66 = about 19.5 uT.

With the magneto body pulling the compass needle East-West, I'd have thought that there's a tangent relationship, i.e. flux density caused by the magneto = Earth's flux density in horizontal plane times the tan of the compass needle deflection. So, for you, that's 16.7 tan 41 = about 14.5 uT. For me, it's 19.5 tan 45 = 19.5 uT.

It's probably safe to assume that the flux density caused by the magneto 15 inches to its side is proportional to the flux density in the centre of the housing (where you want it) and that the constant of proportionality is the same for any K-series magneto. I know from my uncalibrated (but linear) gaussmeter that the flux density in the centre of my magneto that caused the 45 degree compass deflection was 156 KenFgauss. So, it would seem that the flux density at the centre of your magneto is 156 x 14.5/19.5 = 116 KenFgauss. I also know that if I remagnetise the magneto, it reads about 225 KenFgauss on the gaussmeter. So, that all seems to suggest that you mag has only got 116/225 = about 50% of its magnetism 

From experiments I've done, 50% magnetism results in about 50% HT spark current, and more than double the speed required to get a spark in the first place.

Of the magneto people in the States, I've only ever heard good reports about Doug Wood in PA. Google "Doug Wood magneto".

Ken.

[RichardL]

Well,  while thinking about all that (applying the tangent to the needle deflection raises a hand that scratches a head), I have a question about magneto construction. On the humpy side,  There is curved piece of material between the laminated pole piecs.  Is that the alnico magnet or a wedged-in piece that holds the actual magnet in place?

Richard L.

[beezermacc]

That's the magnet. The 'humpy bit' houses the magnet which is a bar magnet with its poles in contact with the laminated pole pieces (shaped like cheeks) which are mild steel. You get a better view of the magnet in an MO1 magdyno where the magnet is a bar magnet with its end exposed

[RichardL]

Thanks.

[RichardL]

Posting this in anticipation. I found a local commercial/industrial magnet supplier who has volunteered to re-magnetize my magneto on one of their big machines. I'll be doing this tomorrow, 44 miles round trip. I figure between the magneto and just seeing a cool place, it'll be worth it. Anyway, we have the interstate highway system that will make it pretty quick. I try to get some photos.

Richard L.

P.S. Don't forget to vote for best picture. Vote for whom you will, but be sure to vote.

[RichardL]

Gents,

First, I've decided I will be the unforgivable hound, and remind everyone, again, to vote for best picture of 2010-2011. Erling's efforts should be respected and justified.

On to magneto magnets...

I made it out to the magnet factory and it was quite intersting. They had some really big magnetizers, but the fellow helping me did not know the ampere-turns in them. Anyway , the upshot is that I was able to improve the compass deflection (using the method described in this topic) from 41 degrees to 53 degrees. I'd call that a great improvement. What do you think?

We tried three different magnetizers before getting a good result. The first one, with vertical flux, didn't get a close contact with the housing and I saw little or no improvement. The second one was a tunnel with flux running the lentgh of the tunnel. That one tried to fling the housing out the end of the tunnel and actually seemed to demagnetize a bit. The third was a twin-shoe type and did the trick, so much so that the large bearing race was pulled out from the insulating shim. I thought from the beginning that this would be the right one, but my host was magnetically attracted to the others. In fact, the twin-shoe was just like one I saw charging magnetos on YouTube.

Here are the photos, in order. The fourth photo is a magnetizer not tried. The fifth is the factory (sort'a).  

 

[KenF]

Glad to see from the 'Brightspark condenser' thread that you're getting the mag sorted, Richard.

By comparison, I'm attaching some pics of our remagnetiser and magnetometer.

Ken
Brightspark Magnetos

[RichardL]

Well, that's different. Does it use the laminated poles of the mag to route flux through the magnet, or does it have a circular field, or.......?

Richard L.

[KenF]

The former, Richard. The remagnetising core is put into the mag body so that the pole faces of the core line up with the pole faces in the mag body (one way round or the other depending on where you want North), and then a big capacitor in the black box, charged up to 340V, dumps its charge into the remagnetising core. A lot of the flux gets routed by the laminated steel in the mag body through the magnet. It also has to be said that quite a bit of flux no doubt goes the other way and jumps the 1/8" aluminium-gap in the laminated steel directly opposite the magnet, but whichever way you remagnetise a K1F / K2F / KVF there's no getting away from that (unless there's some technique I don't know about for extracting the magnet out of the aluminium casting). Of course, some of the flux with find a leakage path through the air.

I drive the thing well into saturation, but the question is, 'What is getting saturated: the magnet; the magneto's steel, or the remagnetiser's core?' I have to admit that I don't know for sure. But what I do know is that, so far, I haven't come across a K-series mag that is more magnetised than I can get them, and that includes a K2FC that Groily had remagnetised the traditional way not long ago. So, I'm fairly confident I'm getting them as good as they can be got.

All good fun.

Ken
Brightspark Magnetos

[RichardL]

It looks like it may be the best way to get in very close proximity to the flux path through the pole pieces. In the top photo I posted, the big cabinet in the background is the capacitor bank. The cables are shown plugged into the 800V output, the connections on the front of the cabinet are 1400V.

So, does the magnetizing plug work for all magnetos for which EasyCaps are available?

This stuff fascinates me to my ultimate demise or exposure of stupidity, or both.

Richard L.

[KenF]

The remagnetising plugs we've made so far are designed for use with the K1F / K2F / KVF where the nominal armature diameter is 2". We haven't tried yet, but they would no doubt work with the MO1 magdyno, perhaps with some sheet steel packing to take account of the extra 175 thou (mil) in diameter. Haven't investigated BT-Hs yet.

We are thinking of offering a remagnetising service. Is that something people would be interested in, I wonder. The question is how does anybody tell whether their mag needs remagnetising. For that, were are currently experimenting with a magnetometer that can give you the answer while the mag is still on the bike. Early days for that yet, but if it proves successful, we may well offer it for purchase or hire.

Ken
Brightspark Magnetos

[KenF]

Further to my earlier post, remagnetising is now available. £15 (if provided with the bare mag body) + return P&P. More details at:

http://brightsparkmagnetos.com/products/remagnetisation.htm

Ken
Brightspark Magnetos