So I broke down with a flat battery on Sunday. MPG has always been on the low side - 42 if I am lucky.

However since the car was without battery for an hour it now has a new lease of life and MPG has jumped to 52 so I guess it needed a reset.

Still love my 2008 500 53,000 miles on. Apart from two new door handles and the wiring issue she is going strong.

Just had the belt thingy changed too

Hoping to hold onto her for another couple of years to make the belt and the handles pay for themselves. Then thinking off road model 500X but as its so much money will try to hang onto this. Would make a great first car for James if I can hang on another 8 years......!

Heidi

Heidi said:

So I broke down with a flat battery on Sunday. MPG has always been on the low side - 42 if I am lucky.

However since the car was without battery for an hour it now has a new lease of life and MPG has jumped to 52 so I guess it needed a reset.

Still love my 2008 500 53,000 miles on. Apart from two new door handles and the wiring issue she is going strong.

Just had the belt thingy changed too

Hoping to hold onto her for another couple of years to make the belt and the handles pay for themselves. Then thinking off road model 500X but as its so much money will try to hang onto this. Would make a great first car for James if I can hang on another 8 years......!

Heidi

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With your low mileage I think it can get there with decent looking after.

Heidi said:

So I broke down with a flat battery on Sunday. MPG has always been on the low side - 42 if I am lucky.

However since the car was without battery for an hour it now has a new lease of life and MPG has jumped to 52 so I guess it needed a reset.

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Old batteries use more fuel as they don't charge efficiently. I had a similar ~10mpg jump when I fitted a new battery (actually my first tank on the new batt jumped a full 20mpg!).

UFI said:

Old batteries use more fuel as they don't charge efficiently. I had a similar ~10mpg jump when I fitted a new battery.

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:yeahthat:

Old batteries also have higher self-discharge rates, which also uses more fuel.

UFI said:

(actually my first tank on the new batt jumped a full 20mpg!).

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The new battery may have been charged to a higher level than that which would be maintained by the car's on-board charging algorithms.

The fuel you save with a newer battery means there may be a point at which it's worth changing an older battery on cost grounds, even though the car is still otherwise running normally. If I ever get the time, I'll work out the numbers.

With the on-board systems fitted to cars these days, surely it wouldn't take much more than programming to have the car work this out for itself, and notify the driver accordingly.

The more worrying implication of age-related battery degradation is for hybrids; I wonder how their real-world economy figures will change as the batteries get older (and replacement won't be cheap!)

jrkitching said:

The fuel you save with a newer battery means there may be a point at which it's worth changing an older battery on cost grounds, even though the car is still otherwise running normally. If I ever get the time, I'll work out the numbers.

The more worrying implication of age-related battery degradation is for hybrids; I wonder how their real-world economy figures will change as the batteries get older (and replacement won't be cheap!)

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In my case economy took a huge dip but the battery only lasted for three tanks in it's obviously bad state. So even at a 20mpg loss over about 1000miles it's not really a big cost.

Toyota at least have done very well to preserve hybrid battery life. Mine's still fine after 10 years, it still charges to full and I can still drive around 1.5km on EV (Toyota claims up to 2km but I don't think anyones really ever managed that real world). Still gets 60mpg tanks and is capable of 90+ mpg city if you try a bit. The battery cost isn't as stratospheric as some claim, and Toyota offer a core refund that means a new battery can be bought for ~$2600 and it's actually an easy DIY job if you have a bit of understanding. At that price a new battery would be a 2-4 year payback for the average driver compared to an ICE only.

Nice to hear Heidi, the 500 x prices already are falling which i expected and it looks a quality product as for passing the 500 down is a great idea

I'm curious, demanding more power from the alternator uses more fuel? I though alternator doesn't have much it if at all resistance force place on the engine like an AC compressor?

The power to charge the battery has to come from somewhere. The problem seems to be exasperated by smart alts as they have a higher output than an always on type. Removing the alt entirely and using a deep cycle battery (charged off the mains) is a proven way to gain 5-10% economy.

I charge most of my car batteries off solar panels daily, the MPG boost is measurable. UFI's alternator no longer has much to do, it only engages on overrun

Edit: And as for the A/C compressor, that's a solid 10-25% loss depending on duty cycle (how hard it actually has to work). Biggest hit I've seen from an A/C was 4l/100km. More power to run the A/C than it takes to drive an entire 500! It takes 3kW to drive a typical A/C compressor, if the A/C was running at 50% duty cycle, it would add 25% to a 500's fuel usage at 50km/h.

Never thought that a battery could cause less/more MPG, nice new thing to know.

UFI said:

The power to charge the battery has to come from somewhere. The problem seems to be exasperated by smart alts as they have a higher output than an always on type. Removing the alt entirely and using a deep cycle battery (charged off the mains) is a proven way to gain 5-10% economy.

I charge most of my car batteries off solar panels daily, the MPG boost is measurable. UFI's alternator no longer has much to do, it only engages on overrun

Edit: And as for the A/C compressor, that's a solid 10-25% loss depending on duty cycle (how hard it actually has to work). Biggest hit I've seen from an A/C was 4l/100km. More power to run the A/C than it takes to drive an entire 500! It takes 3kW to drive a typical A/C compressor, if the A/C was running at 50% duty cycle, it would add 25% to a 500's fuel usage at 50km/h.

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These figures correspond closely to my own observations. Most folks don't appreciate the extent to which using the A/C system on a hot day impacts fuel economy.

Back to the electrical system, 1HP = 746W; ignoring losses, on a 12V system, that's the equivalent of a 62A load. In practice, I'd say you'd probably get around 50A per HP out of a typical car charging setup.

Assuming an energy density for petrol of 32.4MJ/l, an engine efficiency of around 25%, and a charging efficiency of 80%, calculations suggest charging a 60AH battery from flat will use about 0.4l of extra fuel; around 42p at current prices.

Charging the same battery using a mains charger will likely use around 1 kWh, currently around 11p.

Flat battery to full battery, using petrol costs 42p
Flat battery to full battery, using mains electricity costs 11p.

How many of us have a flat battery?

I can understand the maths on this, but generally our batteries are almost at full most of the time, so the difference is tiny most of the time.

Thanks,
Mick.

No they're not full :-/

Part of the reason for UFI's better than most economy is the fact that the battery is charged daily off a 40W solar panel.

306maxi said:

No they're not full :-/

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I said, "almost full".
Our battery isn't flat, in fact I reckon it's at 90% or more.

UFI said:

Part of the reason for UFI's better than most economy is the fact that the battery is charged daily off a 40W solar panel.

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If a flat battery costs 42p to charge from flat using the alternator, how much fuel is consumed keeping it topped up via the alternator?

Using a solar panel is obviously the most economical way.

Thanks,
Mick.

PS
I wonder why car roofs aren't covered with a solar panel or two. This could assist or even replace the alternator. It wouldn't take much technology to clutch the alternator in and out as and when required.

Roughly 5% of your fuel bill goes into keeping the battery charged.

UFI said:

Roughly 5% of your fuel bill goes into keeping the battery charged.

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At (say) 50mpg, it consumes 2.5mpg to keep the battery topped up.

Say a fill-up cost £25, it needs £1.25 of it for the battery/alternator.

Quite considerable over a year or so. Say 10,000miles @ 50mpg @ £5.60 per Imp Gallon, means you need £1,120 per year. 5% of that is £56

Regards,
Mick.

Mick F said:

I wonder why car roofs aren't covered with a solar panel or two. This could assist or even replace the alternator. It wouldn't take much technology to clutch the alternator in and out as and when required.

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I've done just this on my work vans. The main down side is that solar panels heat up a lot and transfer so much heat to the cabin that the panel can't possibly pay for itself (as compared to a white painted roof) due to the extra A/C usage. In a cooler climate that might not be a problem but then you wouldn't see much current output either.

Since then I've put the panel up on a roof rack. It shades the roof (cooling the interior) and free air under the panel keeps it cool. Excess solar power runs a small vent fan to help bring cooler air in too. Downside is that if you drive at higher speeds than I usually do the drag of the roof rack will negate any gains from the solar panel.

When I removed my set up to clean up the install (ran for a tank without) and refitted it, I scored my best ever tank with a 6.0/100km on van rated 9.7.

So in short solar works but it's a niche, not really mainstream.

Mick F said:

Say 10,000miles @ 50mpg @ £5.60 per Imp Gallon, means you need £1,120 per year. 5% of that is £56

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Yup, alternator deletes with deep cycle batteries and grid charging are well established economy mods.

So ..................... if I left everything as it is, but put the battery on charge overnight every night, I'd save fuel?

Maybe not £56 a year, but would I save something?

Mick.

In my experience these smart alts respond very well to having the battery pre-charged. The saving seems to be around 5% because the alt will only charge on over run, even on a 200km trip, the alt stays in low voltage (economy) mode. Your battery will last longer and S/S should be more reliable. It's a win-win-win.