I have just accuired a motorbike motor, Rotax V990 from Aprilia RSV Mille -01. 125bhp V2. I`m planning to build a trike with one rear wheel. Basically a car with three wheels.

The altenator is only 400W. For what is it good for? How can I calculate the total power needed in the vehicle? Do I need to take some power losses etc. in account?

Is there any possibiltity to “tune” the alternator to produce more current? The alternator is inside the engine under the cover and directly connected to the crankshaft, like a magneto in moped. Do modern Japanese motorbikes like R1 or Hayabusa have it also like that or how?

400W is approx 30A at 12V.

Total power for your car will be a lot less than any tin-top (fan on, wipers on, windscreen heater on, main beam on, braking, radio on max volume, indicating, fuel pump and ECU+spark, kids watching a video in the back while playing with the electric windows ) most of which you won't have, and much closer to the original bike.

Worse case will probably be fuel pump, braking with full beam while indicating, ECU+sparks. So add those up and add a bit in the best belt and braces engineering style. Depending on your design you may have an extra headlight over the bike so that's the place to worry if any.

You can pull more than 30A for a short time as the battery averages the demand for you but long term you will be draining the battery if you are taking more.

It is plenty, the bike the engine came from will have had:

2 headlights.
2 Sidelights.
2 Taillights
2 Stoplights
and on.
About the only thing the bike won't have had is windscreen wipers and a heater fan, and you're not building a car which will make much use of those.

If you are worried use LED lights, they are available for everything including headlights (but the headlights are prohibitively expensive currently). I'm using all LED except headlights.

Which brand led lights are you using? Where to buy?

I've got a 28A alternator. It's okay even if it's a bit borderline if I have the main beams on and the wipers going at the same time....

30A should be fine.

Anyway if it's a trike you might not have wipers

As stated by others, 400W (30A) should be adequate.

The things that you might be running that draw additional power are:
Additional headlight, definitely needed (55W)
Additional rear light, definitely needed (5W)
Additional fan, optional (60W)
Separate electric water pump, optional (60W)
Cigarette lighter for stuff, optional (12W)
Wipers (what are they?)


LED rear lights (you need good ones if you don't want to be shunted from behind if you have combined brake and rear lights) can save you about 8W, led sidelights at the front can save you about 8W.

HID can save another 15-20W per lamp, and gives good bright lights.


I have read that when alternators get warm that their performance degrades. I don't think this is true for your type (where the rotor is within the engine cases) but it is something to be aware of (I think it is the problem that I am having, that and a crap battery, and the fact that I now have a fuel pump (40W), and all the associated power draw of an EFI system).


Regarding upgrading the alternator. I don't think it is necessary in your case, but it is possible on some bikes. Bikers seem to do it to allow them to fit electrically heated accessories for winter riding (i.e. heated vests, gloves, socks etc.). The cost seems pretty high and I don't know whether it is possible for your bike.

Matt

Just below 28 amp ----- OK for carbs getting marginal for fuel injected.
Don't forget the battery also has to get charged