28 replies to this topic

[amarcd]

I'm thinking of removing the alternator on my hillclimb mini to increase horsepower a bit, does anyone know how much by?. I am currently stripping an old alternator so all thats left is the casing and the shaft so i can still adjust and keep the belt tight. Has anyone done this before and what sort of time does the battery last running just the engine and an electric fuel pump and a rev limiter?

Is there any changes I need to make to the electrics or is it just a case of covering the socket that went to the alternator?
Regards
Alan

[Ibexx]

Personally I wouldn't bother. It will probably give you about 3 or 4 hp extra. Have you looked at the Nippon Denso conversion? That should save you about 2 hp and you won't have the troubles of charging the battery and you can have a smaller battery. I chose the Denso alternator and a Varley Red Top 15. Without an alternator and a normal battery you can probably drive for about an hour.

[TopCatCustom]

Remember that the alternator keeps the system at about 14.4v unless under major load, so your battery at say 12.5v (about 2v lower which is 13% lower) may struggle to do anything well, and your coil will be seeing 13% less voltage which could mean you get a smaller spark. Also you have the constant drain of fuel pump etc which could lower the voltage further, and should you happen to stall or need the wipers etc... well it's food for thought!

I'm not an electric genius but that how I understand it before I potentially get ripped apart by a grumpy ass!

Edited by C4NN0N, 13 April 2011 - 08:40 AM.

[Stevee]

Remember that the alternator keeps the system at about 14.4v unless under major load, so your battery at say 12.5v (about 2v lower which is 13% lower) may struggle to do anything well, and your coil will be seeing 13% less voltage which could mean you get a smaller spark. Also you have the constant drain of fuel pump etc which could lower the voltage further, and should you happen to stall or need the wipers etc... well it's food for thought!

I'm not an electric genius but that how I understand it before I potentially get ripped apart by a grumpy ass!

and with all them issues its lowering BHP

[TopCatCustom]

Some rwd racers drive the alternator from the prop shaft instead of engine, alternators don't have to sping as fast as they do on racers, but if they were geared down then on idle they would be useless, so they run them at propshaft speed which is slower and drags less as not directly connected to the engine. (well it is but I know what I mean!).

I guess we'er limited on how to do that on a fwd mini though!!

[amarcd]

so going by all the answers so far i'm better off leaving it as is, with an alternator rather than with non.

[Ivor Badger]

Most classes specify that a charging system must be fitted, it just doesn't say what charging system. The original trick with the dynamo was to cut the wire to the field coils, which cut most of the drag from charging, but still left you with the weight. So the utltimate cheat was to go to the bike shop and by one of those bike lighting dynamos that you clip to the frame that springs againt the tyre wall. Remove the standard dynamo/ alternator, fit a short belt between the bottom pulley and the water pump and set the bike dynamo to run against the back of the belt. No weight, no drag and it charges when you connect a bulb for demonstration if required.

The voltage of a fully charged lead acid cell in 2.2v, so the battery voltage fully charged is 13.2v. A fully charged Varley or even small car battery will run the car all day at a hillclimb/ sprint. Just don't start it 25 times.

[cooperrodeo]

If the alternator is only providing power for the ignition system and assuming approx 50% efficiency of the alternator, then you will gain in the order of 0.1 bhp by disconnecting it. Perhaps double this if you include windscreen wipers.

If you want to to go uphill faster, you would be better off looking to save weight, like going on a diet.

[dklawson]

Remember that the alternator keeps the system at about 14.4v unless under major load, so your battery at say 12.5v (about 2v lower which is 13% lower) may struggle to do anything well, and your coil will be seeing 13% less voltage which could mean you get a smaller spark.

Regarding spark... by the time the battery voltage impacts the spark voltage you are well down on the cells. The spark voltage is controlled by the gap at the spark plugs, not the coil output voltage, and not by the battery voltage (at least not until the battery is very near being completely discharged).

I was actually going to post what Ivor Badger did. Check with your race sanctioning body regarding whether or not the alternator has to be present AND whether it has to be functional. Those are two separate points... present & functional. If you are allowed to run without an alternator, jump start the engine off another battery when possible. If you start off a different battery, the engine will be able to run for a very long time using the one in your car. Engine starting is what really sucks the power out of a battery quickly.

The comment was made earlier that you may "only" pick up 3 or 4 HP without the alternator. Taken as a percentage of the engine output that is nothing to make light of as it would be significant. However, the gain would not really be that high. Power = Watts = volts x Amps. Let's say your alternator puts out 30 Amps immediately after you start the engine (to recharge the battery). Let's also say that the alternator is putting out 14.5 Volts (not unreasonable). 14.5 x 30 = 435 Watts. 746 Watts = 1 HP, therefore, you are saving 0.6 HP (plus frictional losses for the bearings and belt drive). Chances are that if you allow the engine to warm up a bit before your race (recharging the battery and lowering alternator current output), you would see almost no power lost to the alternator during your race.

[Ivor Badger]

If the alternator is only providing power for the ignition system and assuming approx 50% efficiency of the alternator, then you will gain in the order of 0.1 bhp by disconnecting it. Perhaps double this if you include windscreen wipers.

If you want to to go uphill faster, you would be better off looking to save weight, like going on a diet.

Have you weighed an Alternator/dynamo?

[Timinichelsea]

You could look into getting a small kubota dynamo, these are run on the top Mig's & 7's

[matt large]

majority of autograss racers remove alternator as any little gain is a worthwhile gain.

would manage to run a whole meeting on a fully charge battery, that would include 3 maybe 4 5 lap races with cranking of the same battery. If you used a slave battery for starting then we never had any issues.

Granted not alot of electrics in a grasser, ignition, fuel pump, some maybe a water pump, so depends on how long your runs are for

matt : )

[MRA]

Mini's work best with a large spark... therefore reducing the voltage will have a direct negative effect on the power.

Curious about the proshaft trick.... as the current consumed will have to be replaced, and as far as I know the alternator is more efficient at higher speeds than at lower speeds ..... and for every Amp of current that is required to be charged that will require a proportional amount of engine power or indirectly propshaft power to generate it...

There are of course more efficient alternators, I am lead to believe that the Kubota alternator is very efficient.

[Paul Wiginton]

I tried it and went slower up the 1/4 mile by 3/10s.
Use a Nippon Denso, at high revs they shut off the charging circuit automatically and effectively become just a tensioner which frees up (minimal) hp

Paul

[amarcd]

Many thanks for everyone's input. I have also been looking on Google for general information on this and i've come to the conclusion that that the best thing to do is rig up a switch so that when its at full throttle the alt cuts out giving the extra little bit of HP but when at lower revs keeping battery topped up and running ignition at full voltage. O and cheaper than buying a Nippon Denso