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Car battery in BEC?
fege - 8/7/08 at 10:49 AM

I'm using a R1 engine for my MNR Vortx and since the local SVA authorities only permit 15kW/100 kg I need to weight my car down. I'm planning to use a big, heavy car battery but will this cause any problems for the alternator/rectifier?

Mr Whippy - 8/7/08 at 10:52 AM

no

and I think you have just won the crazy rule award, congratulations

[Edited on 8/7/08 by Mr Whippy]

SeaBass - 8/7/08 at 10:52 AM

In the name of safety and stability I would fit a lead floor too!

Can you remove the weight once the vehicle is on the road??

JC

BenB - 8/7/08 at 10:57 AM

If you make sure the car battery is constantly well charged I suppose it might not complain. If you attached a fully discharged car battery to a bike reg it might not like the current being pulled and let out the magic smoke....

Personally I'd just make a boot box out of 15mm MDF. And maybe make a radiator shroud. Out of lead.

MikeCapon - 8/7/08 at 10:58 AM

I can't see how the larger battery could cause a problem. See here where the very subject is being discussed.

RazMan - 8/7/08 at 11:03 AM

How about using two batteries in parallel for extra weight (I can't believe I just said that )

Richard Quinn - 8/7/08 at 11:06 AM

One of my previous Grassers had a very highly strung Pinto in it. That used 24v starting!

Dangle_kt - 8/7/08 at 11:08 AM

You could make the battery box out of steel girders?

Guinness - 8/7/08 at 11:08 AM

I used a car battery, the standard Sierra one, for about a year with no problems at all on the ZZR1100.

Only reason I swapped in the end was that I saw a bike battery on my local bike dealers ebay shop that was £1 and collection only.

Mike

02GF74 - 8/7/08 at 11:15 AM

hmmm, I am not convinced.

question is what limits the current output of an alternator?

It is the mangetic flux that reaches a maximum when the iron core saturates.

One would assume the electronic components are designed to work in this condition so they are not likely to be a problem.

smart51 - 8/7/08 at 11:23 AM

I believe a bike regulator limits the output voltage by turning the excess into heat. Charging up a big, flat battery will pull the voltage down, giving the regulator an easier time, not harder.

If you want to increase the weight of your car to meet Sweedish power to weight laws, I would recommend a heavy steel floor. The lower down you put the weight, the better for stability. You can then fit whatever battery you want, regardless of its own weight.

Speak to the people on the sweedish locost site. They will no doubt know a lot about this.

RazMan - 8/7/08 at 11:24 AM

quote:
Originally posted by 02GF74
hmmm, I am not convinced.

question is what limits the current output of an alternator?



The voltage regulator surely - this automatically prevents over / under charging but also stops too much current flowing into the battery.

worX - 8/7/08 at 11:28 AM

But as above, a steel floor is usually the way to go, even though as it is a Vortx then I assume the floor is already on the car for you?

Steve

tegwin - 8/7/08 at 11:38 AM

Would it not be sooo much easier to just add some restriction to the intake of the engine???!?!?!?!

Recude the power...and your problem goes away!

Add some variable area intake valves and you could alter the power with a hidden switch

02GF74 - 8/7/08 at 11:45 AM

quote:
Originally posted by RazMan
quote:
Originally posted by 02GF74
hmmm, I am not convinced.

question is what limits the current output of an alternator?



The voltage regulator surely - this automatically prevents over / under charging but also stops too much current flowing into the battery.



hmmm, not convinced.

that is partly correct.
yes - the over voltage is done by the regulator;

as the battery is charged, its emf increases thus the voltage regulator will shut off current to the stator thus reducing the current from alternator.

and this comes into play when the battery is more or less charged.

a battery is charged by passing current trhough it and as it becomes more changed, its emf increases. this means the voltage of the charging device need to increase to overcome the emf for current to flow.

when a discharged battery is connected, the battery's emf will be low - voltage regulator will not come into play until battery starts to reach its charged state; the current being limited by the flux.

(unless someone knows otherwise - alternators aren't really my bag)

[Edited on 8/7/08 by 02GF74]

nstrug - 8/7/08 at 11:49 AM

Problem with a steel floor is that would be kind of a permanent solution.

A heavy car battery strikes me as ideal to increase the weight of the car for the SFRO test and can be easily swapped to a bike battery afterwards. As mentioned, it shouldn't cause any problems with the regulator/alternator, provided the regulator has good airflow to keep it cool.

Nick

fege - 8/7/08 at 11:53 AM

Thanks for the answeres. The battery will be thrown away after SVA (provided I have the strength to get it out ). I'm also considering using a steel floor. As far as decreasing the power I've learnt that the authorities don't like that option and therefore use the original power output figures anyway.

MikeRJ - 8/7/08 at 02:29 PM

quote:
Originally posted by 02GF74
when a discharged battery is connected, the battery's emf will be low - voltage regulator will not come into play until battery starts to reach its charged state; the current being limited by the flux.

(unless someone knows otherwise - alternators aren't really my bag)


Saturation of the magnetic path is certainly a limiting factor, but I think the primary current limiter is the reactance of the stator coils, since they will have a high inductance.

The bottom line is a larger battery will be fine. It won't damage the alternator since charging current is limited by the alternator, not the battery.