Mirage TS Charging Conundrum

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grahamf505

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Hi All

OK, this is going to be a bit of a long post, but wanted to give you all the details so far as to my investigations into finding out why my charging system didn't appear to be charging as it should.  The problem originally started with a flat and ultimately defunct, battery.

So, work done so far in my efforts to fix it...

1. New battery fitted
2. New regulator/rectifier fitted (Electrex RR51)
3. Any dodgy wiring connections between alternator, RR and battery re-made and now good

RR is wired as it should be.  Red wire and green wire from RR to White in Loom and -ve battery post respectively.  White from RR to red/green in loom (generator warning light working as it should).  Two yellows from RR to yellow and yellow/black from alternator.

Voltage across the battery with engine running at about 3,000 rpm is 13.5 without lights and approx. 12.75 with lights on.  Feel I should be getting more voltage than this with the lights on as it's suggests a very marginal (if any) charge that's going into the battery.  Two black wires (sense wires?) from loom left disconnected.

Understand that the original Laverda R/R would have had a sense wire to detect voltage drop with lights on and increase output. This one doesn't, but the data sheet says you don't need it as the internal wizardry takes care of this by monitoring the output lead to the battery.

AC test across the two alternator yellow wires (there isn't a third) shows circa 30V at around 3,000 rpm - all seems good.

Next test was to load test the alternator to see how much current I could pull from it and check it wasn't breaking down under load. Connected two 55w bulbs in series across the two yellow wires and hey presto, I'm getting two very bright bulbs at 3,000 rpm - any more revs and I'd swear they'd blow.

Schoolboy physics tells me that 110 watts takes just over 9 amps at 12v, but I'm assuming I need to do the calc at 30V which would be around 3.7amps so that tells me the alternator is able to sustain output under load.  I guess for a load test to check current draw at 12V I could parallel up a couple more bulbs to double the load and then see what level of brightness I get. However, my fag packet test seems to show the alternator being to maintain voltage under load.

Before this, I rode it for a couple of hours on Saturday with the lights on, after which I stuck it on the optimate. The optimate was charging for 5 hours at 0.8 amp until it brought it up to spec so that suggests I used around 4 amp/hour of battery reserve. If you do the maths with head and tail light on (60W combined) for two hours riding, that would consume approx 10 amps of capacity, plus what's being consumed for ignition, brake light, indicators, etc. So it does seem like some charge is going in there, even if it's not as much as it should be.

Wondered if anyone might have any other ideas as to where I might go looking as I don't want to knacker up another battery by excessively draining it.  At this point in time, I'd prefer to work with what I've got rather than upgrade alternators, etc.

Cheers

Graham

 
Graham I m no whizz but do you have an Odyssey fitted? they don t work on a single phase alternator ? I had one die on me with the TS myself.

Also they don"t like optimates, C-Teks recommended.This might not be the problem, but may help?

Shaun
 
Hi Shaun

Thanks for your reply.

Standard Yuasa lead acid battery fitted.  I might try re-connecting the previous rectifier to see what I'm getting now I have the new battery fitted as that may have been OK.

Cheers

Graham
 
13V with lights on will be about maximum of what the MkI alternator is capable of.

Fit a 20W halogen pilot lamp for daylight running if required, and leave main lights off.  Won't drain the battery during general tootling around.  Has worked for me the last 25-odd years.  Passing through civilised areas with full lighting can be a challenge in the dark hours, or you accept you won't make many friends and dare not return! :D

piet
 
grahamf505 said:
Connected two 55w bulbs in series across the two yellow wires and hey presto, I'm getting two very bright bulbs at 3,000 rpm - any more revs and I'd swear they'd blow.

Schoolboy physics tells me that 110 watts takes just over 9 amps at 12v, but I'm assuming I need to do the calc at 30V
Click to expand...



Graham, your schoolboy physics is letting you down. With identical bulbs connected in series, you're getting half the voltage drop through each bulb. If you were to connect the two bulbs in series to a 12V supply, you'd only draw about 28W and get a very dim glow from each bulb.

You need to connect them in parallel to draw 110W at 12V.

The 55W rating is at 12V. Feed it a higher voltage and you'll get more Watts. So you're better off looking at resistance.

Doing the sums for 12V DC. We know that Power = V x I (I being current), so I = Power/V =55/12 = 4.6 Amps.
Now, the globe's resistance, R = V/I = 12/4.6 = 2.6 Ohms (at normal operating temperature)

So, putting two 55W globes in series gives 5.2 Ohms. Apply 30V across that and you get 5.7 Amps (I=V/R) and power = 172 Watts (Power = V x I). So yes, you're pushing them to about 156% of normal operating capacity.

Ohms Law generally only applies to DC circuits. But applying DC electrical calcs to an AC circuit is valid in this case because a light globe is a pure resistor (no power factor involved).

However, the resistance of the globe filament varies with temperature, so if your globes are glowing brighter than normal, they'll be hotter, which increases resistance and power dissipated. Your overloaded globes may be drawing more like 200W because of the overheated filaments. With increasing voltage, you will eventually get to a point that the globe filament will melt. You could also overheat your alternator coils to the point of failure, which would be a little more tragic than a blown globe.

I don't think there's anything wrong with your charging system. 13.5V (or 12.75V with lights on) is normal for the old single phase Laverda alternator. Anything approaching 200W (uncontrolled) is a pretty good output for that old system.
 
sfcpiet said:
13V with lights on will be about maximum of what the MkI alternator is capable of.

Fit a 20W halogen pilot lamp for daylight running if required, and leave main lights off.  Won't drain the battery during general tootling around.  Has worked for me the last 25-odd years.  Passing through civilised areas with full lighting can be a challenge in the dark hours, or you accept you won't make many friends and dare not return! :D

piet
Click to expand...
Piet, my Mk1 Bosch alternator (formerly HKZ, now converted to BTZ by installing a DMC ignition) is hitting the voltage limit of 14,4 Volts, as set by the R/R, at about 2800 rpm with main lights on and battery charged.
To achieve this, I have incorporated some slight upgradres to the system:
-mains relais to avoid voltage drop/losses at the ignition switch
-relais for the headlight bulb to avoid voltage drop/losses at the light switch
-led instrument lighting (consumption 2W instead of 13,6W)
-lead rear light (consumption 1W instead of 5W)
-lead brake light (consumption 2W instead of 21W)
Excluding the power drawn by the ignition, the conversion to LEDS reduced the power consumption for riding with main lights on from originally 73,6 Watts down to 60 Watts (including the power drawn by the coils of the added relais).

Additionaly, I fed the wires of the 2 alternator charging coils separately to a home-brewn R/R unit, where each coil has its own rectifier bridge and its own set of SCRs, controlled by a common voltage sense circuit.

I can not tell which of the changes did most of the improvement, but the system works perfectly well for me, didn' t touch the Odyssey PC680 during the last 5yrs, let alone recharging it.

The only bit of common sense I usually apply during riding is to switch down to pilot lights when sitting idle at red lights in city traffic.

Regards,
Stefan


 
Thanks all for your insight and suggestions...much appreciated that you took the time to reply..in particular, Dellortoman who marked my homework ;-).  It's great to have this forum as a support network.  It sounds like I should stop trying to fix a problem that doesn't exist and get there and ride it whilst we still have some nice weather ;-).

Absolutely loving the bike.  First Laverda I've ever owned and it's everything I hoped it would be.  The more I ride it, the more I want to ride it.  My wife is getting used to my half hour ride outs that typically last for 3 hours!

One thing I notice about this forum compared to others I've been on is that it's grown up.  Nothing worse than getting silly comments back when you're struggling to fix something that might be obvious to others, but not to yourself as a new owner.

Cheers

Graham
 
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