Technical Stop Start Story

[306maxi]

Hi guys again.
I know that electricity is cheaper than petrol, but that is because of taxation systems.

Electric vehicles only make sense if petrol is highly taxed and electricity is cheap. If everyone bought an EV, the governments worldwide would have to tax electric vehicles to compensate for the lack of tax receipts from petrol and diesel.

My question was if pugging in a battery charger used less energy than running the alternator.

I obviously know that without an alternator, the engine would have more power available at the wheels which converts to better fuel economy.

If we had a garage, I'd have a nice insulated cedarwood garage, install underfloor heating and plug in the car to a charging system and a heating system. I'd save a fortune in petrol ................ but at what cost?

Swings and roundabouts.
Mick.

Not really swings and roundabouts. It will always be cheaper and more efficient to generate power on a larger scale.

 

[Mick F]

I see what you're saying, but maybe I'm not making myself clear.

Unleaded petrol has (some figure) of KWh per Litre. I understand that there's more KWh's in diesel than petrol.

If you consider a fully charged battery, and start your car with it, it must take some number of KWh's to recharge it back to fully charged again.

Does the electricity from a power socket via a battery charger consume fewer KWh's than powering the alternator via the engine?

I would expect that the power socket would be better because the alternator must waste power due to mechanical rotation and friction losses. Therefore, if this is true, why don't cars have two batteries and only clutch in the alternator in an emergency?

Thanks,
Mick.

 

[306maxi]

Like I said it will ALWAYS be more efficient to generate electricity on a large scale....

 

[Mick F]

No, that's not what I'm suggesting.
Power is power. It doesn't matter how it's produced. It could be "free" from a solar panel if you want.

I would expect power consumption from an electric socket to charge a battery would be less than creating the power via petrol/diesel to rotate an alternator.

I reckon it can only be mechanical friction losses that make an alternator power hungry.

Thanks,
Mick.

 

[306maxi]

Of course. If you're not losing anything through friction then it'll be 100% efficient aside from resistance......

But that's simply never going to be possible in a car.

 

[UFI]

Unleaded petrol has (some figure) of KWh per Litre. I understand that there's more KWh's in diesel than petrol.

If you consider a fully charged battery, and start your car with it, it must take some number of KWh's to recharge it back to fully charged again.

Does the electricity from a power socket via a battery charger consume fewer KWh's than powering the alternator via the engine?

I would expect that the power socket would be better because the alternator must waste power due to mechanical rotation and friction losses. Therefore, if this is true, why don't cars have two batteries and only clutch in the alternator in an emergency?

It's too late and too hot here to do the math for you but as Maxi said it is far more efficient to use grid power (or if you had a solar panel and MPPT controller with no other use ).

Petrol contains 8.87kWh of energy. The engine is 30% efficient and the alternator around 80-90% but you still have to factor losses from drive belts etc, so you'd be lucky to get 2kWh for every 9kWh you pay for.

If you charge at home you'll see roughly 90% efficiency with a good charger.

Batteries are very inefficient at full charge but that applies much the same whether an alt is charging them or the grid.

Many cars now do have alternators that disconnect (electrically) when not needed, if you have S/S, then you have such an alt, there really should be an electro magnetic clutch too, but it wouldn't make much difference as most alts are now on a serpentine belt so the mechanical losses are still present. The actual act of spinning a disconnected takes next to no energy.

FWIW, hypermillers have tested the effects of alternator drag and have agreed on roughly a 10% milage improvement via a physical alt delete (on older cars with separate alt belts), and 5% with simple electrical isolation. Some run deep cycle batteries (ie sometimes two) size to suit their required range. The hard core remove the alt completely, others remove the belt for easy recommissioning. A electro clutch as found on an A/C compressor is an alternative, but again needs to go on the drive side, not on the alt itself for real gains. Others boost the 12V system with Life cells.

With a smart alt, precharging achieves much of the above with little effort.

 

[Most Easterly Pandas]

OK bare with me. Smart call their Stop start car with Smart Alt, a micro hybrid. So if a 500 with S/S is a micro hybrid, adding a bigger starting battery and plugging it in every day makes it a Micro PHEV (OK the EV bit is a bit sketchy, so maybe it's a Micro PH, but then that's an entirely new term).

I was able to do around 100km yesterday and the alternator only ever kicked in on decel (it will always ramp up on overrun) even with the A/C, DRL's and radio on.

PHEV

Plug-in Hybrid Electric Vehicle.

Can't be plugged into the wall
Hasn't got a Hybrid energy source
Isn't an electric vehicle

So its anything but a PHEV.

All Smarts system does is basically have a posh unit which is a starter and alternator all in one, and uses the momentum of the car slowing down to charge the battery, when this energy instead would have been wasted as heat through the brakes. And even this system is poorly designed and causing massive issues with age from what I've seen - the major advise to new buyers is to not touch one of their MHD engines with a barge pole!

UFI said he has a solar charger.
Is that a free lunch?

Probably only a solar maintainer, and not an actual charger so to speak

 

[Sweetsixteen]

I reckon it can only be mechanical friction losses that make an alternator power hungry.

It's more than that Mick.
As the alternator charges the battery it meets resistance. All generators do, because they're producing power - and you can't get out for nowt. The more power the alternator is required to produce, the greater the resistance. That's one reason why cars use more fuel at night than during the day. The resistance drains power from the engine, which uses more fuel to compensate.
Friction losses within the alternator are a very minor drain by comparison.

 

[UFI]

So its anything but a PHEV.

All Smarts system does is basically have a posh unit which is a starter and alternator all in one, and uses the momentum of the car slowing down to charge the battery, when this energy instead would have been wasted as heat through the brakes.

Who says it has to be plugged into the wall? It can be plugged into a charger instead right?

A S/S Fiat works the same ways as the MHD, the alt ramps up on over run and during braking. With a precharged battery, the alt only kicks in on over run, that's enough to keep the battery full, even with DRL's and A/C on.

Probably only a solar maintainer, and not an actual charger so to speak

40W garage mounted panel + MPPT controller. It will recharge a 120Ah from ignition off to float charge in 30mins.

 

[Most Easterly Pandas]

40W garage mounted panel + MPPT controller. It will recharge a 120Ah from ignition off to float charge in 30mins.

Fair enough. I assumed it was a £30 solar maintainer available from the likes of Halfords etc, my mistake.

Who says it has to be plugged into the wall? It can be plugged into a charger instead right?

It doesn't run on electricity, you're charging an ancillary battery and not a traction battery, this is why its not a PHEV. Its still not and EV or an Electric Hybrid.

A S/S Fiat works the same ways as the MHD, the alt ramps up on over run and during braking. With a precharged battery, the alt only kicks in on over run, that's enough to keep the battery full, even with DRL's and A/C on.

No it isn't, they're completely different systems with completely different principles and operating methods. I'd advise having read up on it, as it has some interesting operating methods and should work well in theory but just seems to be poorly executed.

Fiat's system will charge when ever charging is required, not just on over run. In addition to this the Fiat system has no way of using the alternator to operate as an engine brake, the belt tensions and strength are nowhere near high enough - which is one of the main features of smart MHD system.

 

[Mick F]

Thanks guys, very interesting.

In the old days, even cars with small engines were lucky to get 30mpg. These days, we're eeking out every last drop of economy and small gains regarding battery charging are important.

Cast you minds back to the 1950s and 60s when cars had dynamos and voltage regulators, let alone carburettors and mechanical ignition systems.

Regards,
Mick.

 

[UFI]

Fiat's system will charge when ever charging is required, not just on over run. In addition to this the Fiat system has no way of using the alternator to operate as an engine brake, the belt tensions and strength are nowhere near high enough - which is one of the main features of smart MHD system.

Surely the MHD will also charge when required? If I charge UFI's battery I've done 100km so far and the alt's only been charging on overrun/braking.

When the alt on the 500 engages under the right conditions, I can feel it increase my engine braking, it's not a lot of course, but it is recovering energy that would be lost as heat otherwise. The way a S/S 500 works is very similar to MHD, just in a less aggressive way. It still can't 'drive' the car, so it's not a 'hybird' either.

 

[Most Easterly Pandas]

When the alt on the 500 engages under the right conditions, I can feel it increase my engine braking, it's not a lot of course, but it is recovering energy that would be lost as heat otherwise.

Interesting, never once felt this on our 500, or our other Fiats with smart alternators fitted.

 

[UFI]

You'll really need to be looking for it. It's very slight, but (I think it's an 80A unit) it's capable of generating 1.5hp, keeping in mind the car only needs ~7hp at cruise. It will be most noticeable with a fresh, fully charge battery, as it will ramp up from zero load at cruise to full output with the brake switch pressed (I've been playing with a forced regen switch on my Renault, in parallel with the stock brake pressure switch). You may also find there's a slight 'bump' when braking just enough to engage the switch but not enough to build any real brake pressure.

With a weaker battery it will go from low output to higher output, so less of a difference.

 

[Sweetsixteen]

.



Cast you minds back to the 1950s and 60s when cars had dynamos and voltage regulators, let alone carburettors and mechanical ignition systems.



Regards,

Mick.

Yeah! Give me more! Love the old dynamos, and rv's - and carburettors, and distributors.
You could really play about with that lot - like new brushes, cleaning and re gapping the commutator, altering the spring rates in the distributor, re grinding the needles in the SU - etc.
Even do these things at the roadside, and be a Good Samaritan.
Different world now.

 

[UFI]

So update on my non S/S 110Ah battery. Now seeing 76mpg over an A-B-A test drive in the hills, with a passenger on board and moderate A/C use and still having a bit of fun as appropriate The engine's still fresh so I think my 80mpg tank is well within reach. I think with skinnier tyres and lightweight wheels 100mpg is within reach. Keeping in mind my real life MPG is usually better than the factory display too

Looks like my going to a small capacity LiFe battery was the wrong way to go. The 110Ah battery will probably replace the 10 year old one in my Jeep to make way for a ~60Ah LiFe, LVC and Supercap

 

[Mercky]

Interesting. What's the ah capacity of a standard SS battery? My mpg has gone to hell recently but also my SS is doing the 10 sec restart thing so perhaps related?

 

[Mick F]

Standard SS battery is 60Ah.

[ame]http://www.amazon.co.uk/Varta-Start-Stop-EFB-Battery-027EFB/dp/B00842JYQC[/ame]
This one is working well. I've yet to calculate the mpg figure and compare to before, as I've only filled up once since fitting it.

I have found, that only using the car for a mile or two at a time, the SS stopped working. This is because the battery takes miles/time to recharge and I wasn't doing enough mileage to keep it topped up. A session on the charger sorted it.

Since then, the car has been used for longer at a time, and SS is still good.

The original battery was bench-charged and left in the shed. It still shows up as 12.3volts - it is now four weeks since it was charged, and as far as a battery is concerned, there's nothing wrong with it. It would be absolutely fine in a non-SS car.

Regards,
Mick.

 

[Most Easterly Pandas]

For those wanting a cheap pulse charger, Lidl have them in currently at under £15

 

[larslarsen]

So update on my non S/S 110Ah battery.

....

I also prefer to replace a car battery by a new one (if necessary) with the largest possible capacity, fitting into the holder.
Unfortunately, in my TA the original 60Ah battery fills the holder already.
How did you install a much larger 110Ah battery?