Twin battery

[Paul]

Two batteries on my 100, is it a 24v starter like the 80?

I would go out and look but i've had far too much wine and its much too dark

 

[Julian]

Yep, 24v start

 

[uHu]

No, no, no.
No 100 has 24 v start from factory. It's 12 volts through and through.
And I don't think anyone would be adventurous enough to modify one.
The two batteries just make it easier to position enough ampere-hours in the available space.

 

[Julian]

Mine does

 

[Paul]

 

[Julian]

 

[uHu]

Mine does

You're special.

 

[Julian]

Thank you

 

[Jon Wildsmith]

The EWD only shows 12v start, I assumed diesels still had twin batteries because of the extra current load from whatever heater arrangement they have?

 

[Julian]

Aghhhhh found out


Always liked to think it was 24

 

[frank rabbets]

Why the .... did they bother with 24v in the first place? Did they have 100,000 24v spare starter motors that needed a home?

Frank

 

[uHu]

The reason is loss. I.e. loss of voltage. When you need a 3 kW starter, there will be a high current flowing through it, and that current flows through the battery and cables as well. At 12 volt, the current will be 250 Amps. At 24 V only 125 A. The higher the current, the higher the voltage-loss through the cables and terminals. If at 250 A, the voltage loss is 2 V, then at 125 A the loss is only 1 V. Than factor in that 2 V is 16 % of 12 V, while 1 V is only 4 % of 24 V. That means the loss of power in the 12 V starter is four times that of the 24 V starter.

This is slightly simplified, the difference can be even bigger. But as this is all theoretical, and not considering adaptations done to rectify the problem, it's good enough for highlighting the problem.

So, in the end, with all the hassle of change-over relay etc, it is better and more reliable to design the 12 V starter for a bit lower voltage (to compensate the loss) and then use thick and short cables.

 

[frank rabbets]

I was thinking that the same power would be needed to turn the engine over whatever the voltage so the watts would therefore have to be the same but wondered why they had the 24v system in the first place. The big tractors I used to drive in 1965 had big diesel engines, sometimes at -5 deg c, but had one large 12v battery.

Frank

 

[uHu]

I was thinking that the same power would be needed to turn the engine over whatever the voltage so the watts would therefore have to be the same but wondered why they had the 24v system in the first place. The big tractors I used to drive in 1965 had big diesel engines, sometimes at -5 deg c, but had one large 12v battery.

Frank

Yes, the same power at any voltage, but as the power is a product of volt times ampere, the amperage is bigger at 12 volts, and therefore also the loss.
Also the LC has no problem starting at -25C with 12 volts.
It's just that it is easier and cheaper to make a system for higher power at a higher voltage, but then do it for the whole vehicle, like on a bus, or a lorry. There is btw a study suggesting that the ideal voltage for car electrics on a non-electric car is 42 volts...

There is a reason for high power lines (your typical huge overhead power line) to use a very high voltage -- less loss and lower cost.

 

[frank rabbets]

I threw a 5 amp fuse wire 30ft long over a 440,000 volt pylon cable to prove to my friend that no damage would be done. Just a "click". Unfortunately it arced down the vaporised copper , burned my trousers off and blew a hole in the road. We both ended up in Wolverhampton eye infirmary, blinded for 48 hours. Volts X amps at that voltage equals a lot of energy. Womboure tip 11.00 p.m. 1979 after a Friday night drinking session.

Frank

 

[frank rabbets]

P.S. High voltage pylon wires are aluminium, I think, which are cheaper in material and lighter to support. However the resistance is higher with aluminium. I have never been able to work out whether they use aluminium at a high voltage to take advantage of this, or that high voltage is used for another reason.

Frank

 

[uHu]

Some experiment
Glad you survived.

At that high voltage, there is another feature that comes into play: That the current mainly flows on the surface of the conductor. Therefore it is better to use thick conductors, with more surface, and that is easier with a light material. Those wires have a core of steel, for strength, and the fact that steel has a specific resistance three times that of aluminium doesn't matter as the current flows on the outside, where the aluminium is.
And aluminium is a good conductor. Of the normal metals, only gold, copper and silver are better, and copper prices keep rising.

 

[frank rabbets]

Thanks uHu. Hope your 100 is running OK.
Sorry about Norway's problems.


Frank

 

[Paul]

Guys, lots to ponder there.

By the way, the sticker on the side of my starter says 12v