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DT 175 MX 12volt conversion

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My plan was to convert my DT175MX from 6 volt to 12 volt and if it worked then do the write up.

However, a fellow DT rider, kiln was also doing something similar but had only upgraded the regulator and bulbs.
So I brought forward the write up but the project is not finished yet and I can't say that it works 100%.
(as I've not had enough time to evaluate the success.) I may have to edit this post in the future!
i can say it works 100% I updated the topic after 9 months of use at the end.

Disclaimer. This is what I did to my own bike, i can't be held responsible if you fry your electrics or your own bike if you try repeating it. tongue.gif
It's up to you to satisfy yourself that the advice, solution, method is right for your bike

Why ?
As many of you will know the DT175MX and I'm sure many other bikes are 6volt.There are many reasons why manufacturers use 6v instead of 12v
They don't fit 6v for the fun of it, after all they spent their money doing the research. However, a lot will be to do with physical sizes of the generator itself and to some extent the space available for the parts to be stowed on the bike.

The late 70's, early 80's DT range is one of these bikes.
It has a physically small generator in comparison to other bikes around during this period. Many bikes of this time were 12volts, but their generators were much bigger, afterall you don't get something for nothing.
The good news is time changes many things. I can't imagine many new bikes today are 6volt, advances in Electronics and technology will ensure you don't ride around in the dark!

Some guys in the past have tried to convert their bikes to 12v some clearly fail and some no doubt succeed, I hope to be one of the latter!

I purchased my DT175MX at the beginning of 2011, two weeks later it failed its MOT...on the lights and horn. They were not adequate for the test: whilst the indicators did indeed flash, the brake light thought it was an indicator too.
The horn sounded like a fart, and not a very loud one at that!
The culprit was poor earthing, but once fixed it did all work, but it wasn't a sound and light show.
The MOT guy suggested converting it to 12volt to avoid problems like this in the future and was confident there was probably a 'kit' somewhere which would do the trick. Sadly, after many hours of trawling the net I couldn't find one. There are indeed plenty of 12v conversions for other bikes, just not the smaller DT range, but one thing's for sure they weren't cheap either!!

I then spent more hours trawling the net and came across the post in the forum about the guy who swapped his magneto over for one from a 12volt Honda C90 cub,
Take a look here the trouble was he never finished the write up and never said it worked without any problems..maybe he set fire to his bike in the process. ohmy.gif

Nonetheless, the very fact that a modern 12volt system could be, in theory, transplanted into the ageing DT filled me with inspiration. I set about doing my own home work and started project 'firefly' (Small glow-worms which emit very small amounts of light just like a DT175!) biggrin.gif

Part 2 to follow

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A bit of theory Einstein. Any concerns about wiring.?

Will the wiring for 6v be ok for 12v?

Yes it will. Its all to do with amps and a few electrical laws

Do you recall at school, you only needed any 2 values to get the third?

Volts = watts divided by Amps V=W/A

Amps = Watts divided by Volts A=W/V

Watts=Volts times Amps W=V x A

Not very inspiring is it? Let me apply it to the DT.

The main headlight uses a 6volt 35w bulb

As we have the watts and volts, so we can use the above equation to work out the Amps it uses. This can be written as 35W / 6V = 5.8Amps

so the wiring deals with 5.8A simple? Eh?

Therefore, if you replace the bulb with a 12v /35W one.

35 w / 12v = 2.08 A

The Amps loading is half and subsequently the wiring does not need replacing. Of course you need to add up all the bulbs on the circuit to get the total number of amps the wiring has to cope with, but it will always be half the amps the 12volts needs when compared to 6volts.

Or you can look at it another way in fact 6 volt wiring has to cope with MORE amps than 12v. Clear as Mud I hear you say!! Trust me this is how it works, the wiring will be fine.

However, My DT175MX's wiring is now over 30 years old and one of the reasons it failed the MOT was poor earthing. Unfortunately, it wasn't just a clean up of the frame ground which allowed the lights to work again. I had to clean up EVERY contact. All the connectors were badly tarnished, the wiring in places is quite brittle and on closer inspection the copper wire has gone green. This increases the resistance of the wiring and means the electrical flow will be impaired adding further problems.

All these are signs that over 30 years the atmosphere had got into the copper and oxidised it. At the end of the day, nothing last forever, and the 30 year old loom will need replacing. I'm only replacing mine because its old and the resistance is higher, but all the conversion was done on the existing loom.

Part3 next..the lighting coil biggrin.gif

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Part3 The lighting coil
Let there be light.

My Dt has three coils, Two source coils which are attached one on top of another and are part of the CDI (electronic ignition) One of these creates the spark at low revs the other at higher revs. Used together this way, maintains the spark across the revs range.
The other coil is the lighting coil. It has two windings over one core. One winding terminates as a white wire and is responsible for the charging the battery. The other wire, the yellow wire runs the 6v lights.

Because it’s only a small coil, (12 volt coils have more windings) it’s output is limited. Nonetheless, it will still generate 12volts. The trouble is you don’t get something for nothing and it takes a lot more revs to do so

With the engine running and the generator disconnected from the rest of the bike, the output is as follows: Read the RED scale on photo below of the meter for AC volts.
Yellow wire (lighting circuit)
2000 revs = 6v
4000 revs = 11.5v
5000 revs = 14v
6000 revs= 16.5v

It’s the function of the regulator to ‘clip’ the voltage to 6v thereby maintaining the 6volts across the revs range.

White wire (charging circuit)
2000 revs = 11v
4000 revs = 18v
6000 revs = 26v

this wire is the charging circuit and it too is clipped by the regulator so the voltage remains steady. This circuit also runs through the rectifier. This device can be likened to a one way valve and ensures the voltage only goes in one direction to charge the battery.

So it can be seen that there is 12 volts output from this coil, but you need higher revs to get it. the other factor is that changing the regulator to a 12v means the voltage will be clipped to 12 volt above 4000 revs hence the reasons the lights go dim on tick over and up to about 3500revs. (you can’t tell 11v from 12v)

In theory you could run the lights off the charging circuit and use a 12volt regulator to maintain the 12 volts, but you wouldn’t have anything to charge the battery. Having said that you could simply run everything off this circuit without a battery! I might give it go just to see what happens!! biggrin.gif


Reads: 0-5-10-15-20-25-30



Part 4 next, any other options before we start!

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This is how I understand it to be.

The regulator has no other purpose than to stop you blowing headlight bulbs, it has no function in the charging of the battery, the battery simply acts as a soak as was common with many small bikes of the era. (essentially they are two circuits) it is an AC regulator and the headlamp (only) runs with AC.

Great post so far NEO ;)

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Thinking about it though I might be wrong in believing that. The lighting /charging coils hace two windings, so by regulating one...depending on the construction of the coil maybe the other is regulated too...

easy to prove this, just unplug the regulator and measure the battery voltage, if it rises considerably, it is indeed regulated by said regulator

I better shut up :rolleyes:

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The regulator has no other purpose than to stop you blowing headlight bulbs, it has no function in the charging of the battery,

Don't shut up mate, but the regulator is involved in the charging circuit.

Part 3b The Regulator

As you can see from photos the white wire output (charging coil) is over 6volt in fact it goes well over 25 volts, what stops this increased volts frying your battery as you ride? the regulator.

On the 6volt regulator, it clips the volt to 6 volt, in your words its acts as a soak, which is probably a better description it certainly gets warm which is why it has those cooling fins, but it has an internal threashold which means, it 'soaks up everything above 6volt.

Take a look at the wiring diagram of the DT and the internal switch arrangements.
[from generator:- Lighting circuit yellow wire:charging circuit white wire]

In position 1 on the ignition switch, (engine run on lights off) the white wire from the generator goes to the switch and is connected to the yellow/white wire to the regulator. In essence soaking up the excess volts which would fry the battery.

In position 2 (engine run, lights on) the yellow wire from the generator is switched to the yellow/white wire to the regulator. The tail light and pilotlight (parking light) are both on drawing current from the battery.
Switch the headlight on, the regulator 'soaks up' the excess current, in essence, and you're right, stopping the bulbs blowing.
This 'draw' on the circuit causes the field in the generator (remember its the same coil) to partly collapse, thereby reducing the output from the white wire which prevents the battery frying.

Elementary physics? or have I turned into brian cox!

Here's a simplified diagram from later on in this thread, brought forward here to show the connections.

The block shows the connections within the ignition switch making up the circuits in the various key positions of I, II, III.


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Any other options?

My original inspiration came from the post about fitting the Honda C90 stator plate and CDi unit as a whole into the DT.

The way it is described suggests you have to sacrifice your flywheel to obtain the collar part to fit the C90 flywheel onto. The two flywheels fit but are not aligned with the woodruff key and the timing needs to been adjusted.

Swapping the entire stator plate means you also sacrifice the DTs own CDI unit which works fine as it is, You have the potential to lose the power of the spark at high revs, which is why my DT has 2 source coils for this.

The other concern is on the DT the pulser coil is on the inside of the circle so to speak, on the C90 the pulser is on the outer circle and will only fit in one position in the crank cover, hence the reason why the timing needs to be adjusted as its all slightly misaligned.

Going by the original poster he got his DT working with this set up, but he never got back to us to tell us how successful it actual was.

Anyway I don’t want to replace the CDI unit on the DT the set up works just fine. It’s the lights which are the problem.

The potential good news is if you really want to swap the 6v lighting coil for a 12volt one, the C90 is 12 volt and the unit on the whole is the same size as the DT, which means the lighting coil may fit providing the magnets of the DT flywheel give it clearance and the fixing holes are the same.

The other promising part is that the C90 has a large following and many alternative hybrids utilise the C90 engine.

Which means new dirt bike stators to go on C90 based engines are easily available and they are all 12 volts, including the lighting coil. Even better they are all under £20 new.

However, I kept the 6 volt lighting coil, because of its power output as seen in the photos. Which also means you don’t need to worry about removing the flywheel, well not today anyway!

Still interested? Part 5 shows the parts needed to make the 12v conversion,

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Any other options?

........... which is why the DT has 2 source coils for this.


You have said this a couple of times NEO but actually the majority of Dt175's had only one source coil, all the later square section swing arm ones. Of course they were different spec and a different CDI but worked equally as well, maybe better ;)

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Oooops I must confess my knowledge is a bit limited on the various models. :blush:

My research comes form the forum and the ol' Haynes manual.

I've corrected my posts to reflect this.

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Cant wait for part 5, sunglasses at the ready :DB)

I'm intregued too, my only thought so far is all those voltage figures were no load. How much actual power can that little coil handle?

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Part4a That little coil beavering away!

The measurement for Power in electricity is the WATT.

that little coil produces 0 to 20v plus on the charge circuit

and 0 to 16v on the lighting coil

On the 6v original system the Bulbs on the lighting circuit

Headlight and 3 instrument lights

all add up to 45.2 Watts

(The indicators,flasher unit,tail/brake,pilot,neutral,oil,indicator telltale and horn all run off the battery)

The total wattage is 35w +10.2w = 45.2Watts

(3.5w x3 =10.2 main beam tell tale + 2 x instruments lights)

Thats the POWER of Watts the lights use, its probably not the limit of the wattage the coil produces

If we replace all the bulbs with the same wattage but in 12volts

the wattage remains the same, its still 45.2Watts

the total AMPS used by the 6volt system is 7.5Amps (45.2w/6v) (Amps=Watts divided by Volts)

the total Amps when its 12volts will be 3.7Amps (45.2w/12v)

The difference is the coil produces 6 volts at low revs but generates over 20 at high revs.

To produce 12volts at low revs there needs to be more windings the Watts output may well be lots more but the lights will still only uses 45.2watts maximum

I think I know what your concerned about but its the Watts which are the key.

If you turn on two 60watt bulbs indoors you still use 240volts but consume 120watts of Power. you don't have 480volts going through the mains.

Does this help? :blink:

I'm busy writing the next few parts....Its almost exciting isn't it? :D

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yes almost exciting indeed but what is the point of keeping to a 35w headlamp. It's the 35w that gives the light, does it matter whether it's 35w from a 6v supply or a 12v supply? they will both be the same brightness? I dont see where the 'upgrade' aspect is :unsure:

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Am I not winning you over?

I wasn't able to buy a headlight bulb in anything higher than a 35w one.

But the taillight is noticeably brighter and at higher speed the headlight,I must confess, does look brighter to me.

However, I think the upgrade aspect for me comes from having a 12 volt battery to deliver much brighter indicators a brighter brakelight and a more powerfull horn. You can't run an airhorn off 6 volt.

If the car user can see my intentions and the pedestrians move when they hear the horn, then surely its got to be worth it?

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I was kinda hoping you would say that you can now see where you are going on unlit roads though, I remember how bad they are in these conditions. Good point about the horn though, are you saying that tiny battery can handle a stebel :o

My DTR is 12v and its a 2003 bike, the headlight is just the same, it shuts down at idle and gives an orange glow at above idle, I wouldnt dream of using it on unlit roads, but hey I'm a lot older now and dont stray that far :D

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Part 5

What needs to be changed and how much will it cost!

The biggest stumbling block in the past is trying to source a 12volt battery small enough to fit in the same space as the 6volt one.

Well, good news folks, there is one…hurray!

Battery codes are : YB3L or FB3L or CB3L

The dimensions are:

Length 98mm Width 56mm Height 110mm (the 6volt one is 6N6-3B-1 : 99mm x 57mm x 111mm)

These 12v batts are listed for:

Cagiva 350cc T4R (1987-90)

Fantic Motor 125cc Raider LC

Fantic Motor 250cc Raider LC

Honda LS110 TH (1989-92)

Honda CG125 -IR (1992)

Honda MTX125 RW RW-TH (1985-90)

Honda NZ125 (1993)

Honda NSR150 R R2 (1994-98)

Honda MTX200 RW (1985)

Honda XL200R (1983-1984)

Honda XL250 R (1984-87)

Honda XL250 RC (1982-83)

Honda XL250R (1982-87)

Honda XL350R XR350R (1984-87)

Honda XL500R (1982-87)

Honda CRM50 (1993-94)

Honda MBX50 FW FWD S SD SWD (1985-87)

Honda MTX50 FR RS S (1985-89)

Honda NS50F NS 1 (1990-99)

Honda NSR50 A F (1987-95)

Honda XL600 R (1983-87)

Honda CRM75 MTX75R (1989-94)

Honda MBX75 FW (1983)

Honda NSR75 (1992-1994)

Honda MBX80 SW SWD 2 FWD (1985-87)

Honda MCX80 S (1983)

Honda MTX80 R2 RS (1987)

Kawasaki KDX125 A1-A4 SR (1994-95)

Kawasaki KDX125 B1-B4

Kawasaki KDX200 B1-B2 (1984-92)

Kawasaki KH125 K7 - K10

Malagutti Runner VS Rally (1987-90)

MBK 50 X-Limit DT50 (1997)

Yamaha DT50 R (1989-1997)

Yamaha V100 (1993-94)

Yamaha DT125 LC (1984-87)

Yamaha DT125 RE (1988-96)

Yamaha RX150 (1995)

Yamaha DT200 RE (1993)

Yamaha SDR200

Yamaha XT250 (1984)

Yamaha XT350 H N (1985-00)

Yamaha XT500 (1986-89)

Yamaha DT80 LC LC II (1983-96)

Yamaha RD80 LC II (1983-86


I used the AGM Motobatt gel battery MB3U order code ASIN: B004EE2I62 available from Mad4bikes via Amazon.co.uk (cheaper than ebay) £19.99 (02/2011)

The conversion will require:

12 volt battery (see sbove)

4 x indicator bulbs 12v/21w

1x tail/stop bulb 12v 21/5w

1 headlight bulb 12v/35w

1 pilot bulb

6 x dash bulbs (oil. Neutral etc)

1 x 12v flasher unit

1 x 12v Combined Regulator/rectifier

2 lengths of wire and connectors

I already had all the bulbs from my car spares and box of bits kept over the years. I had to purchase the battery £19.99 and the flasher unit £3.50 from the local car accessory shop. The 3 hole headlight bulb came from a buy it now on ebay for £1.75. The regulator was on ebay for £4.99 no one else bid! New ones can be obtained for about £15. Postage was free on the battery!

The cost to me was under £30 and most of this was the battery! :)

If your aging 6v battery needs replacing then for a little more expense you might want to consider the conversion…… B)

Part 6 next how to wire it into the DTMX

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:D Great stuff Ne0! This exactly what I was looking for!I highly suspect my problem also lies with the 6v rectifier and seperate 12v regulator.Can you please give me direction to a model of 12v regulator/rectifier I can search for on eBay or even Yambits?

Maybe you can include model or part numbers available in a project pdf download after the whole write up is complete?

I can't wait for episode 6...sorry part6 etc. ;)

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Part 6 contains all about the regulator, should be done before the weekends out....

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Part 6 contains all about the regulator, should be done before the weekends out....

NE0, If at all possible, please include picture of the connectioins into the loom.I looked around on the net and I see aome inexpensive 12v regulator/rectifiers with 5 wires available for mainly the chinese GY6 engines.Only trouble is which wires are incoming and which are outgoing and how can this benefit us...(Wire colours are yellow,pink,green etc. I can't wait till the weekend as I would love to apply these alterations as soon as I have a chance. Thanks again for all your knowledge and research made available for all.

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