Revs go up - Volts go down

Message

randomsquid · #1 Post by **randomsquid** » Tue Mar 06, 2012 8:47 pm

Took the bike off the optimate the other day and pressed the go button. It just went urgh. Took the seat off and shoved the old Gunson smart charger on it and half an hour later it started more or less before it had a chance to turn over. So either the optimate or more likely the lead to the battery is playing up.

I've got one of those optitest multimeter for dummies things so I plugged that in and the numbers on that matched the numbers on the dash.

Here's the thing. Ticking over it reads about 13.3 although it does drop a touch and occasionally wanders up to 13.6. Rev the bike to 4 grand and it drops to 12.9. This doesn't strike me as healthy.

Am I going to have to bugger about with it?

MartDude · #2 Post by **MartDude** » Tue Mar 06, 2012 9:08 pm

I don't know if the Futura & Falco are identical in this respect, but that's a well-known issue with Futuras which have the OEM reg/rectifiers

randomsquid · #3 Post by **randomsquid** » Tue Mar 06, 2012 9:43 pm

I don't know but it doesn't sound unlikely.

If that's the problem then I'd guess the easy option would be one of those mosfet reg/recs from the States?

Last year I went through all the connectors and didn't find any gunge or melted bits.

MartDude · #4 Post by **MartDude** » Tue Mar 06, 2012 10:04 pm

I fitted an Electrex reg/rect soon after I got this bike (nearly 4 years ago now), and I've never had any charging problems. I have no idea what the voltage output is now, but at the time it was acceptable.

But that was before the mosfet things became so fashionable

#5 Post by **mangocrazy** » Tue Mar 06, 2012 10:06 pm

On another forum I frequent (for old VFRs) a very popular mod is to fit one of these:

http://www.ebay.co.uk/itm/150479033981? ... 1423.l2649

It's a natty little tri-state LED gizmo that monitors battery voltage and changes colour accordingly. One of the few weak points on VFRs of a certain vintage are the reg/recs, annd this gives advance warning if the RR is going South. I'm toying with the idea of fitting one to the Falco as a precautionary measure.

anzacinexile · #6 Post by **anzacinexile** » Tue Mar 06, 2012 10:18 pm

Whoah - steady boys

What you're seeing is perfectly normal and expected. Its caused by the rectifier diodes taking a finite time to switch. The faster the motor runs, the higher the frequency of the AC current from the alternator so the higher the losses become.

What is obvious is your volts are a little low so you can either do the infamous wiring mod or do what I do at every service and thats clean the plugs 'n' sockets with switch cleaner. There's the 2 brown connectors that join the alternator to the regulator and the white connectors that sit after the regulator and I see a healthy 14.6 volts @ tickover falling to a perfectly respectable 14.2 @ 4000rpm

randomsquid · #7 Post by **randomsquid** » Tue Mar 06, 2012 11:58 pm

mangocrazy wrote:
It's a natty little tri-state LED gizmo that monitors battery voltage and changes colour accordingly. One of the few weak points on VFRs of a certain vintage are the reg/recs, annd this gives advance warning if the RR is going South. I'm toying with the idea of fitting one to the Falco as a precautionary measure.

Thanks for that.
The testmate mini I have does a similar thing (duno why I thought it was called an optitest, old age maybe) but with separate leds for each step.
I'll try lashing that in the cockpit somewhere and watch what happens. It's waterproof and has a couple of holes for cable ties. I'd just have to get an extension for the optimate lead.

randomsquid · #8 Post by **randomsquid** » Wed Mar 07, 2012 12:04 am

anzacinexile wrote:
What is obvious is your volts are a little low so you can either do the infamous wiring mod or do what I do at every service and thats clean the plugs 'n' sockets with switch cleaner. There's the 2 brown connectors that join the alternator to the regulator and the white connectors that sit after the regulator and I see a healthy 14.6 volts @ tickover falling to a perfectly respectable 14.2 @ 4000rpm

Thanks for the explanation, I gave them a dose of wd last year but I'll pull them and clean them with switch cleaner and see what happens. Have to be next week though as the suspension folk have got it this weekend. I've looked at the wiring mod. It frightened me.
Priorities - 1 make it handle - 2 make it start...

MartDude · #9 Post by **MartDude** » Wed Mar 07, 2012 12:04 am

As a matter of interest - do Falcos have the same problem with the brown connectors as Futuras - do they melt & occasionally catch fire if neglected? Just curious.

MartDude · #10 Post by **MartDude** » Wed Mar 07, 2012 12:08 am

anzacinexile wrote: the higher the frequency of the AC current from the alternator so the higher the losses become.

Would you mind explaining that a little further, please, in layman's terms? Not doubting you for a minute - just inquisitive.

D-Rider · #11 Post by **D-Rider** » Wed Mar 07, 2012 12:48 am

MartDude wrote:
anzacinexile wrote: the higher the frequency of the AC current from the alternator so the higher the losses become.
Would you mind explaining that a little further, please, in layman's terms? Not doubting you for a minute - just inquisitive.

..... How deeply do you want to go into the quantum mechanics of this Mart?

... or will the simple answer suffice that it takes a finite time for the diodes to start conducting and ramp up to being fully switched on. While they are "turning on" they effectively have an impedance which means that power is lost (well, dissipated) through them (you'll notice they get hot)
When the frequency is higher they are being asked to turn on and turn off more frequently .... but this period during which they transition from being off to on is of the same duration - but a longer proportion of the cycle - therefore the overall losses increase.

MartDude · #12 Post by **MartDude** » Wed Mar 07, 2012 1:22 am

D-Rider wrote:
MartDude wrote:
anzacinexile wrote: the higher the frequency of the AC current from the alternator so the higher the losses become.
Would you mind explaining that a little further, please, in layman's terms? Not doubting you for a minute - just inquisitive.
..... How deeply do you want to go into the quantum mechanics of this Mart?

... or will the simple answer suffice that it takes a finite time for the diodes to start conducting and ramp up to being fully switched on. While they are "turning on" they effectively have an impedance which means that power is lost (well, dissipated) through them (you'll notice they get hot)
When the frequency is higher they are being asked to turn on and turn off more frequently .... but this period during which they transition from being off to on is of the same duration - but a longer proportion of the cycle - therefore the overall losses increase.

I did say "in layman's terms"

That is both comprehensible and satisfying to my curiosity, ta very much.

anzacinexile · #13 Post by **anzacinexile** » Wed Mar 07, 2012 8:36 am

MartDude wrote:
anzacinexile wrote: the higher the frequency of the AC current from the alternator so the higher the losses become.
Would you mind explaining that a little further, please, in layman's terms? Not doubting you for a minute - just inquisitive.

....or, its all down to pixie dust and magic

anzacinexile · #14 Post by **anzacinexile** » Wed Mar 07, 2012 8:38 am

MartDude wrote:As a matter of interest - do Falcos have the same problem with the brown connectors as Futuras - do they melt & occasionally catch fire if neglected? Just curious.

I've never heard of them catching fire but I've seen a few melted examples "over the other side".

Like most things, a bit of TLC occasionally goes a long way

anzacinexile · #15 Post by **anzacinexile** » Wed Mar 07, 2012 8:40 am

randomsquid wrote:
anzacinexile wrote:

Priorities - 1 make it handle - 2 make it start...
Aahh but if it doesn't start then you dont have to worry about it not handling surely