DIY Car Maintenance with function over finesse!!

[myglaren]

Interesting hypothesis with a fair chance of being correct.
As at last some cars with DPFs turn on everything electrical to get the alternator to load the engine and create more heat then I reckon it is highly likely.

[MattBLancs]

Let's take the 9 amps figure for quick bit of maths:
9 x 14 Volt = 126 Watts.

Guess / trusting AI result on alternator efficiency:
55%

From
https://www.google.com/search?q=alterna ... #cobssid=s

= 229 Watts.

Drive belt efficiency
From
https://www.google.com/search?q=multi+v ... s-wiz-serp

93%

Gives 246 Watts.

From memory 745 Watts= 1 horsepower so the above is

0.33 BHP.

Compared to max output, a drop in the ocean, but compared to typical pottering about (that might need "10-20 bhp" or so) it's a reasonable percentage.

From
https://www.google.com/search?q=hp+to+d ... e&ie=UTF-8

AI also thinks we'd need about 5 bhp to maintain idle for a 2.0 petrol, so 0.33 is definitely beyond insignificant.


Usual disclaimers about trusting AI and/or anything you read online anywhere!

(Edit to capitalise Volt in honour of Mr Voltaire, seems churlish gives I've got my Watts capitalisation sorted! )

[mickthemaverick]

Entertaining stroll through some numbers there Matt but I don't see why you started with the 9 amps figure. That was the current drawn from the charger with just the battery as a load. When in the car the current drawn from the alternator would be the current load of the car + the draining load of the battery. So the question really is by what percentage does the battery load increase the load on the alternator. So if in normal running the current to run the car, for ease of numbers, is 20A then the old battery would be adding almost 50% more load meaning the energy transferred to the alternator by the engine would be 50% more than necessary to run the car, hence with new battery the engine would have considerably less load which would free up that power for driving the wheels!! or maybe not!!

As most people are aware I don't agree with the concept of AI, let alone what it does or doesn't say, at all and G****e is a strict nono in maverickmansion

[Rp0thejester]

What's this University degree in maths time!!?? Keep it simple pls

[moizeau]

Just get back to the carb Ryan

[CitroJim]

Just get back to the carb Ryan

Indeed Any progress on that front Ryan?

[MattBLancs]

Entertaining stroll through some numbers there Matt but I don't see why you started with the 9 amps figure. That was the current drawn from the charger with just the battery as a load. When in the car the current drawn from the alternator would be the current load of the car + the draining load of the battery. So the question really is by what percentage does the battery load increase the load on the alternator. So if in normal running the current to run the car, for ease of numbers, is 20A then the old battery would be adding almost 50% more load meaning the energy transferred to the alternator by the engine would be 50% more than necessary to run the car, hence with new battery the engine would have considerably less load which would free up that power for driving the wheels!! or maybe not!!

As most people are aware I don't agree with the concept of AI, let alone what it does or doesn't say, at all and G****e is a strict nono in maverickmansion

Yes, correct I used the 9 amps (as what the charger was putting into the battery) deliberately - in reality the alternator will be supporting the car's electrical demand and charging the battery. But, with the new battery in place, it's still having to support the car's demand - so in terms of what you felt, there's no change there as that load on the engine does not change.

Sorry for the maths overload and agree "AI everything" as is the current fashion is perhaps the bigger worry with energy consumption.

[mickthemaverick]

Apologies for a cursor misplaced, I have inadvertantly deleted my original post about the car running smoother with the new battery, when I was intending to quote from it!! . However I did say I would relate my further thinking after comments had been made. There have now been some interesting comments so I think a clue to where my thinking took me is warranted:

MTM Original thinking

[Rp0thejester]

So you're basically taking a old idea used in heart transplants and doing it on a battery?

[mickthemaverick]

My thinking at the beginning led me to wonder whether the alternator could have a similar clutch type mechanism fitted to enable the alternator pulley to be free running under predefined conditions. Then following the operation of the clutch the alternator would engage and supply power in the usual way. My thinking was similar to that in a hybrid really, where you only use the alternator to charge the battery when the engine is being turned by the wheels under engine braking conditions, So my thinking was to switch the alternator in and out of use to reduce the load on the engine under strong acceleration for example, so if you kick down then the alternator load would be removed allowing all the engine power to drive the car. When on overun the alternator is engaged to replenish the battery driven by gravity, after the battery had been solely used to run the car when alternator pulley running free.

That thinking was modified at lunch when Zel pointed out that you wouldn't need a clutch mechanism, simply a relay to cut off the feed to the field coils which ten allows the alternator to spin freely.

So leaving aside the engineering my basic idea was to rearrange the charging system so that charging was only carried out at say up to 1/3rd throttle and then removed when you need the power for overtaking or hill climbing etc. Having seen the difference in my car with a good battery fitted I felt that overall efficiency could be improved by a selective charging regime!!

[Hell Razor5543]

I would make a couple of modifications to the system. First, you cannot take the alternator out of the loop until the battery has a full charge (as the battery will then have to drive all of the electrics), and second, the alternator can only be disconnected for a maximum of 5 minutes (or when the battery drops below a certain charge).

[mickthemaverick]

Yes James, explaining more of my thinking would basically mean the Voltage dropping below say 12.4V (could be adjustable from a pot and voltmeter on the dash) would bring on the charging and only cut it off when back to 12.7 say. Also I would make it that turning on any high load accessories, eg heated rear window etc would automatically bring the alternator online. However normal cruising in daylight could be accomplished for significant distances on the battery. I know that because I drove one of my cars 165 miles with a broken alternator belt on the way to Devon. Fortunately the water pump was on a seperate belt with the power steering pump and the alternator had its own.

[Rp0thejester]

Would it be at all possible to have 2 alternators doing or a bigger one to accomplish the same job/ease on the engine?

[mickthemaverick]

I don't think that would help. Fundamentally you need to convert mechanical energy to electrical energy and the electrical load defines the energy required from the mechanical system. So whether you have 1, 2 or a big one the only difference it may make would be if the combined efficiency of 2 or even a big one was better than the efficiency of the standard unit. Unlikely since they are all the same type of unit. Undoubtedly it would be possible to design and build a more efficient one but the costs would make that prohibitive.

[MattBLancs]

Interesting thoughts

My understanding:
Agree with Zel, an alternator that isn't charging is only bearing (and brush rings) friction, plus a bit of fan load.

Also those AC electromagnetic clutches have a fairly big current draw I believe, so could be drawing current to generate current! (And worse if you had a control failure whereby you'd not enough charge in the battery to activate the clutch to enable th alternator to charge the battery - you'd be in a Catch 22)

Reversing the clutch operation: energised to release would solve the above and "fail safe" but then would consume current to save current! Ever more counter productive!


I've wondered for a while about improving efficiency in a different way - as you'll know, engines are much less efficient until warmed up, to anything that shortens the warm up time would be an efficiency benefit. As such, I on occasion have an idle read about water cooled alternators - reasoning to myself that an alternator at high load (seeking to replenish a battery that just fed the starter motor) would be just the ticket to feed heat into the engine coolant.

BMW and VW both seem to have dabbled with water cooled alternators - for packaging/heat dissipation issues (on big V8 / V10 TDI engines) and also on a curious other application:
Renault Espace 1.9 D.

The VW and BMW items look very "integrated" but the Renault item looks to be a couple of hose tails to plug into. If I see one for twenty quid on eBay I might grab it "for a play"