Why is KERS restricted?

[dp35]

Perhaps the question of this topic should begin with what is the potential energy recovery for KERS anyway?

In a recent interview, Lewis Hamilton said that the KERS system they were using could capture & store 160% of the engery they were allowed to use per lap.

[autogyro]

Perhaps the question of this topic should begin with what is the potential energy recovery for KERS anyway?

In a recent interview, Lewis Hamilton said that the KERS system they were using could capture & store 160% of the engery they were allowed to use per lap.

160%?

[Fil]

Perhaps the question of this topic should begin with what is the potential energy recovery for KERS anyway?

In a recent interview, Lewis Hamilton said that the KERS system they were using could capture & store 160% of the engery they were allowed to use per lap.

160%?

basically they claim to have run a system capable of building & storing about 10.5sec of KERS per lap..

[xpensive]

Perhaps the question of this topic should begin with what is the potential energy recovery for KERS anyway?

In a recent interview, Lewis Hamilton said that the KERS system they were using could capture & store 160% of the engery they were allowed to use per lap.

The way I understand the rules, you are allowed to store as much energy as you wish, but you can only discharge 400 kJ (or 400 kWs, as I prefer that when it comes to mechanical energy) per lap at a maximum rate of 60 kW, why I think what Hamilton is saying is that they can store as much as 640 kWs per lap.

But this should be depependent on the track, when one of the problems with KERS must be the short duration of braking, perhaps 15-20 s per lap, which in turn challenges the efficiency of the MGU and battery at a 60 kW charging during a 2-4 s rush?

The lead-acid battery in my car holds 70 Ah, which at 12V is the equivalent of some 3000 kWs, and takes forever to charge.
The Li-Po battery in my cell-phone is 3.4 Wh, or 12.2 kWs, why I wonder how that would react to 3 seconds of 2 kW charge?

[machin]

160%?

I'm not that surprised... if there are 10 braking events per lap you only need to store 40kJ in order to achieve the 400kJ per lap maximum allowance... of course you'd only get 0.666 seconds of 60kW boost after each corner which isn't that great... the team's obviously provide much more than this which allows them to use all 400kJ on one straight... if the cars have 400kJ storage and there's the same 10 braking events per lap and no restriction on energy discharged per lap the systems CURRENTLY EMPLOYED could potentially release 4000kJ per lap!***

That's why I don't like the current rule of only 400kJ per lap....

***(That assumes that all 10 Braking events are long enough to recuperate the full 400kJ)

[xpensive]

As Hamilton said, their current KERS-system is good for charging 160% of the 400 kJ over one lap, not 1000%, machin.

[machin]

I don't think you can really second guess EXACTLY what Hamilton meant;- he could have meant that their system can store up to 640kJ any any given time... if that's the case then if the 400kJ per lap were lifted then he could use his KERS boost after every corner and actually use much more than 640kJ per lap, assuming that the braking events are long/frequent enough....

Alternatively he could have meant that the system can store say 64kJ maximum at any given time and therefore on a lap with 10 braking events each of just over a second he could, if the rules allowed, use 10 separate "boost" events each of just over 1 seocnd duration and 60kW boost...

Or something between these two scenarios....

The 160% is basically meaningless without knowing all the details....

[xpensive]

It's rather simple really, when the MGU is 60 kW, 15 seconds of braking time over one lap will never give you more than 900 kJ.

If you consider an aggregated efficiency of 70%, 640 kJ sounds very reasonable.

[machin]

I agree: -somewhere between 600 to 900kJ per lap with a single 60kW motor/generator should be possible but my point is that you cannot determine whether he means:-

1, That the car can store a total of 640kJ at any one time, or

2, Whether it can actually only store a lot less at any given time, but if it stores then uses that storage and then stores again it can capture more than the 400kJ its allowed to discharge in one lap..

Either way the Hamilton proves the 400kJrule is rubbish!!!!!

[xpensive]

Hamilton obviously means that the McLaren system has a 60% overcapacity in energy-storing for the 400 kJ discharge,
which is only natural when the 60 kW MGU serves both as generator for charging (15-20s) and as motor at discharging (6.7 s).

With the 60 kW MGU, you theoretically need 10.66 seconds to charge 640 kJ, even if the entire system has a 100% efficiency.

There is no corner, on any F1 track anywhere, with that kind of duration on the brakes.

[flynfrog]

the over capacity may be there to so that they are charging in the efficient part of the batteries. It takes much more energy to add 1Ah to an almost full pack as apposed to a 50% full pack. They might have calculated that the added weight of the larger pack was worth the gain in charging efficiency

[machin]

There is no corner, on any F1 track anywhere, with that kind of duration on the brakes.

I think you might be further misunderstanding me; I agree that storing 640kJ in one braking event with 60kW is impossible; as you say; the duration required is WAAAAYYYY too long.... But is hHamilton suggesting that in any given instant the car could have 640kJ of energy stored onboard? We just don't know from his comment....

But all this does prove that the 400kJ rule is rubbish.... the cars are carrying around a capability that they cannot use..... remove this rule and Hamilton's car (according to his quote) would have over 10 seconds of 60kW boost per lap... not 6 seconds...

[autogyro]

Kers can harvest energy during any off power condition, it depends on how it is configured. It is not brake dominated.
The cars are not accelerating all the time and any time other than this in theory becomes available for harvesting.
Depends on the fuel usage trade off.

[machin]

That's a good point... any time that the car normally wouldn't be at full throttle the system could use any excess engine power to charge the system... it wouldn't help fuel economy (it would mean you'd be at full throttle for longer, but not all the energy would be used to accelerate the car), but it would mean that you could have the "boosted" power level for longer (If there wasn't the 400kJ per lap rule!!!!

[xpensive]

If you really want to make a mockery of things you should charge for a few seconds at top speed, when the power-loss would cost you the least time-wise. As aerodynamic power-loss has a cubic relation to speed, losing 60 kW when accellerating at 200 km/h or when flat-out at 300 is a world of difference.