General Alternator Capacity Query

jfheath

jfheath

John Heath
Joined
Mar 18, 2006
Messages
3,143
Age
71
Location
Ilkley, W Yorkshire, UK
Bike
2013 ST1300 A9
This isn't specifically ST related, but I'd like to know anyway.

My brother has purchased a very nice looking Deauville NT650V2. Nice looking little brother to the ST and I must admit to having looked at them with a keen eye in the past.

He wants to fit some daytime driving lamps. So I start delving into the circuit diagram. There are some very interesting figures in there.

The total value of the 6 fuses in the fuse box is 46A (4x10A and 2x3A). The main fuse on the starter relay unit which supplies the power to all of these fuses is 30A
So it is clear that if all of the fuses were subject to their maximum power rating, the 30A fuse would blow without affecting the individual fuse. That's OK - its normal to put in the next higher rated fuse to protect a circuit. But it means that I can't rely on the fuse value for finding any spare capacity.

The lamps would need to be connected direct to the battery anyway - with its own fuse and with a relay. That's not a problem either.

Ive edited my original post - I referred to an 'alternator', but in view of @mjc506's post, I need to change this to 'stator' or 'generator'. The fiches say 'generator'.

The battery has an 8 Amp/Hour rating, and the generator is .24kw = 240W (which is about 20A to keep the maths simple).

There's a distinct possibility that the 2x60W driving lamps (say 10A to keep the maths simple) that he want to install will exceed the capacity of the generator, and the extra power demand will then be taken fromt he battery, which will eventually go flat while he is riding. So if there is no spare capacity on the generator the full 10A will have to come from the battery, which gives him about 48minutes.

All of this I can understand and work out for myself. For example, brake lights, both headlight filaments, indicators, horn are not drawing power all of the time, and the battery can provide the power and then recharge for the periods when they are not being used. So in effect, I can dismiss some of that power demand.

But my knoweldge hits a buffer at that point. So the question is (and you knew I'd get there eventually).....

What happens to the generator if the load of switched on equipment exceeds the capacity of the alternator - apart from the fact that it cannot charge the battery ?

Does it risk damage ? Does power start to flow from the battery and try to operate like a motor? Does it overheat ?

I haven't got a clue.

I'm sure less inquisitive people would just stick the lights on the bike and not worry about it and say it seems to work. I don't know how many of them then get left at the side of the road with a flat battery !
 
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I think if you ran anything at max draw for extended periods of time it might not end well. It's a motor and will heat up. It's also harder on bearings as it's working harder. Heat kills, how quickly? "It depends." No one's ever stated what the expected lifespan of an alt is under normal bike load without farkles and why some alts die early and some go forever.

Alternatively I don't know how much excess an alternator at speed puts out that is dumped by the VRR as to prevent frying the battery. I think there's as much a mechanical issue as well as electrical component in this equation.

This is indeed a good question.

As far as the extra lights, is your brother going halogen/incandescent/HID or LED? Two 60w lights leads me to think they are not LED, which would certainly help with the draw.
 
Is the Deauville an alternator or in-flywheel-stator?

Either way, if you draw more power from the system than the generator is able to 'produce', then the excess will be drawn from the battery, which will eventually go flat. The alternator/stator will likely produce more power as battery voltage falls, but not by much, and that will cause increased load on the alternator.

If it's a car-style alternator (like the ST), its regulator will be varying the field current to regulator the output power (well, actually, changing the field current will change the output open-circuit voltage, but since the alternator will (should) never be open circuit, it's pretty close to regulating current into the battery). So less electrical load means less (thermal) load on the alternator and less (mechanical) load on the engine. Overloading a car style alternator will usually kill the rectifier diodes first (overcurrent and thermal damage to the diode). But alternators are usually pretty over-designed so can withstand quite significant overloads reasonably happily.

If it's a more-'normal' stator within the flywheel, then it's slightly different... Instead of the wound rotor of the alternator, giving variable field strength, there are permanent magnets mounted to the flywheel: a fixed field strength. This means a fixed open-circuit voltage/nearly constant power output for a particular rpm, varying nearly linearly with rpm. Most motorcycle regulators then regulate system voltage/current into the battery by shorting the output of the stator! ('Shunt' type. At high frequencies/varying duty cycle) This does various strange things with stator voltages, but the main effect is that the stator basically runs at maximum power all the time (which also means mechanical load on the engine doesn't change with electrical load) and any 'extra' power generated by the stator that the bike's electrical system doesn't use is burned up as heat in the regulator and the stator. So higher electrical load gives a cooler running regulator... Some (usually aftermarket) regulators operate differently, and instead 'open-circuit' the stator (again, at high frequencies/varying duty cycles) to regulate power. This is kinder to the regulator (runs cooler at lower electrical load), and results in less electrical load on the stator, but can result in high voltages in the stator (but this shouldn't matter much if the stator insulation is in good condition. Potentially more electrical/radio noise)

For a car-style alternator, or a switching style regulator, I'd be tempted to 'encourage' lower wattage LED driving lights (and headlights etc etc) to reduce electrical load - cooler running, less mechanical load on the engine, more spare capacity for battery charging or other accessories. For a 'shunt' regulator, there is some benefit to having a slightly higher electrical load to keep the regulator and stator a little cooler, but you still don't want to exceed the rated output. I'd still go for LED driving lights :) (the system will have been designed to mange the stock system, and LEDs would be a smaller additional than halogens, and you still want to leave plenty of margin for charging the battery etc).

A small voltmeter visible to the rider wouldn't be a bad investment...
 
As a point of information the NT650V Deauville does not have an automotive style alternator. It has a conventional stator/generator type fully contained within the engine cases.
 
I'd echo @mjc506's suggestion regarding a dash mounted voltmeter. If you exceed the alternator's capacity, the voltage will drop from a normal 13+ volts into the low 12's as the battery makes up the difference.
 
Simply, the bike uses the power it needs to run the engine and lights, and any left over charges the battery, unless you're trying to use more of that excess power for accessories, in which case the battery contributes.

Even then, it is very unlikely to actually discharge the battery of a bike that is being ridden, because much of the load is intermittent, such as turn signals and brake lights, leaving plenty of capacity for accessories.

What matters is that the battery charges more than it discharges over time, so the average current into it is additive, rather than subtractive. Sitting just idling is a very different story; the alternator needs RPMs.
 
I’ll put in a plug here for voltage monitors instead of a volt meter to keep an eye on electrical system. These consist of a single LED that flashes green, show steady green, show yellow or flash red depending on the voltage present in the electrical system. It’s what I install so the state of charging is apparent with a glance. The LED is tiny and installs easily in a multitude of locations on a motorcycle.

www.signaldynamics.com

Head's Up™ Voltage Monitor

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Single LED Voltage Monitors - Gammatronix

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dduelin said:
As a point of information the NT650V Deauville does not have an automotive style alternator. It has a conventional stator/generator type fully contained within the engine cases.
Click to expand...
The successor (pretty much identical engine design except enlarged displacement with EFI + ABS added) NT700VA had an OEM front fog light kit in the accessory catalogue (and a fog tail-light, and a stereo with 6xCD-changer, and a satnav kit, and heated handles...) which seem to work with 2 pcs H7 bulbs; would need to dig deeper to see if they'd beefed up the alternator and/or rectifier there...
OTOH would selecting an LED kit be the more conservative/safe decision...
 
Wow - thank you for the replies. Matt's reply was excellent - very detailed and full of the the sort of stuff that I knew nothing about, but everything that has been said is adding to the overall picture. I think that I was probably right to be concerned. It's not something that I have ever had to worry about on the ST1300.

And - yes, I think the Deauville does not have an alternator - it has a 'Stator' - it shows it as a 'Generator' in the fiche headings. I knew of the terms magneto, stator, alternator, generator. I didn't know the difference ! I'll go back and change the word 'alternator' to 'generator' in my original post to keep it the same as the fiches.

The lights that my brother is considering are LEDs but still 125W combined - so 10Amps (ish). But whether they are quoting power consumption, or have quoted a wattage to compare brightness with Halogen bulbs, I don't know. I'll do a bit more digging for him to see what else is out there for lights.
 
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Sounds like 'halogen equivalent' (sales crap) to be honest, but worth double checking actual amp draw :)
 
Most of the LED lights out there - well, I should say many - inflate the lumens but state the wattage draw of the lights correctly. Most of the LED's in use now are good for 100 to 125 lumens per watt, with some newer ones upping the higher number somewhat. Spiderman told me that it's better to go by the wattage (over the lumen output) for this reason. I admit to some confusion when reading the advertising descriptions - are they telling me the total wattage for two lights or the wattage for one? In these cases, I go back to lumens or look at similar fixtures.

As an example, if most 2" lights that can be mounted low on your forks are listed as 1000 lumens and 10 watts each, but the one you are thinking of buying says it is 20 watts and 2000 lumens, it is a good guess the latter is for the pair. Note that higher end luminaires like Clearwater or Denali might have outputs higher than the lumens/watt noted above.
 
The first thing to do is change all the halogen lights to LED's.
This will save you some power that you can apply to the extra lights.
For example your halogen headlight is 65 watts, dropping to a 33 watt LED will save power and give you more light.
Go LED for day time driving lights, more is better, that are spread out, than a few that are brighter.
Mellows bike is a good example of many lights. Also set of yellow zoom lights down on the forks would set him apart.....
But you may have limitations on what you can do, since you are on the other side of the pond.....
Watt for Watt you will get about a 5:1 increase going from halogen to LED.

There might be a Stator/regulator upgrade but that might be more work than it is worth.
 
Additional tip: Change flasher to an LED-compatible one if you install LED signal bulbs, and not resistors that waste the energy usage you're trying to reduce.
 
oude geit said:
So do I understand you have a 240w power source, feeding a 360w fuse (30a). And you want to add more load....
Click to expand...

Yes, that is what it amounts to, although the sequence is the other way round. He wants to add more demand, but I'm telling him that he has only a 240W generator, and that it may damage the generator or it may leave him with a flat battery part way into a ride.

As fair amount of the current demand that is catered for in the fuses -tnis far from continuous. So does the extra load damage the generator, or is it just supplied by the battery. Matt has already given as good an answer as I could have wished for.
Honda may have taken this into account leaving no room for additional farkling.

The separate problem is ensuring that the generator is able to recharge the battery when the temporary power demands are not required if these regular but temporary loads do not present problems for the generator.

Flash, brake, hazzards, horn are respectively. 60, 21, 84, 36 watts max = 201w So that is a bit under 16 amps must be catered for within the main 30A fuse. But even a 30A power draw exceeds the capacity of the generator.

The safest way is to fit led lighting all round, perhaps disable the flash button (60w), and then use the figure for the wattage that has been saved as the maximum for the driving lamps. That keeps the total current draw within the original specs.
Eg if (say) LED bulbs half the wattage, then just replacing bulbs would save 35w continuous and 52w intermittent. Plus 60w if the flash/pass button is never used. That would be plenty to play with - 147w - if as @spiderman302 suggested that LEDs halve the wattage.

I've never done this on my own bike. I'll have to start researching what lamps are available.
 
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Flash, brake, hazards, horn are briefly and intermittently used and the extra power required is easily handled by the battery. What you have to watch is the continuous power needed.
fuses values are way over what is needed otherwise you would be blowing them often. your most likey only using less than half of the available power. so there is margin to add lighting/farkels.
 
Agreed. Except I think in this case I think that Honda may have taken that into account already. The total fuse value is 46A. The main fuse that feeds them is only 30A. The generator puts out only 20A. I'm using the 20A figure as a safe maximum, yet those intermittent devices use 16A if they are all on together. So I suspect that my leeway has all been used up.
 
I'm with Spiderman here John. I'd pretty much ignore the intermittent loads, the battery will definitely fill the gaps. I think the easiest and best solution to retain the draw you have now is save the wattage with the headlamp bulb, so go LED there and just fit Led axillary lights. You should really be back where you started with minimal work.
I spose at a later date if other bulbs blow then consider LED upgrades there too.
Good luck.
Ray.
 
JMHO but as evidenced by my XL600 the battery is a ballast; dead or probably even missing, it kick starts easily but doesn't run or drive as well; being a thumper with the variation in alternator excitation, voltage ranges considerably and it feels notchy.
I think the battery will tandem with your alternator when net draw exceeds alternator capacity, which will vary according to rpm and eventually your measurable [combined] system voltage will "brown down" under sustained excessive amperage draw until things start to go sideways
 
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