Battery voltage low ?

I would have thought 11.64 was much too low even under load

As previously stated, if you switch *everything* on, including the heated front screen, there is no way that the alternator can balance the load. The HFS on its own draws around 60 Amps! You will be drawing a lot of the current from the battery, which is why the voltage will drop below 12 volts. (Under this situation, you can often hear the alternator scream in protest!)

FYI, Ford mitigate against running the battery low by only allowing the HFS to turn on when the engine is actually running, and by turning it off if the monitored battery voltage drops too low.

Chris

I'll have to get the meter out and check when the weather picks up but under those circumstances it seems the battery would possibly run flat even with the engine running. Given an average tick over of 1000RPM I would have thought that the alternator would have still put out enough to stop the condition occurring.

With respect, you thought wrong.

Petrol versions of the Focus have an alternator with a maximum output of either 70 or 80 amps; diesels 90 amps.

If the HFS takes 60 amps, that doesn't leave much for the rest. Even cars generally (other than those with HFS IOW), will struggle to balance the absolute full electrical load at tickover.

In point of fact, the total possible system load must be around the 100 amps mark.

Remember that both screen heaters switch off automatically after a few minutes, and the front screen heater will switch off if the battery voltage (as monitored by the Smart Charge system), goes too low.

As a rough guide (and I know it's not strictly linear), if the HFS was on for five minutes, five minutes daytime running with little electrical load would recover the battery to its previous state. (In case you don't have a HFS, I never needed mine on for more the five minutes in 10 years of use.)

Maximum alternator output will not be achieved with an engine speed of

Chris

The heated front screen takes a huge amount of current so that it clears quickly, then switches off. IIRC, it won't allow use if the battery is marginal.

Engine electrics etc are all designed to work down to about 8 volts or so

- for when starting on a very cold day.

Thanks Chris. That's very interesting

In message , "Dave Plowman (News)" writes

Putting a meter across the battery with the starter turning on a cold day would be scary for a few seconds. A few 100 amps through the internal resistance will nearly kill a tired battery. :)

Yes it was the constant load that was confusing me. Apparently the CPU will not allow certain equipment to stay on if the drain is too much.

I have a very accurate digital voltmeter sitting across the battery, fed via an ignition switched relay. Fitted the LED unit in the speedo. Even with a new fully charged battery, the volts drop to under 10 when starting on a cold day.

To add- the battery MUST be the correct silver calcium type to work properly with the smartcharge system, the system is unable to fully charge a standard lead acid type, and while it will work for the most part, you may suddenly find yourself with a flat battery during the colder months when demand is high.

Secondly, if you were measuring battery voltage at a HOT low idle (which on a 1.8 is 600-650rpm) the smart charge reduces alternator output down to about 25% so not surprising with that loading that the battery voltage was low. Try again at 1500-2000rpm.

Tim..

Just replaced the Original Bosch battery on a 97 Volvo S70. Pretty impressed. The new one (Varta) definately won't last as long.

Tim.

It was my understanding that the special Ford battery required a higher voltage to charge it fully. If this is so, why will a standard one not he fully charged?

IIRC, they are owned by the same company and made in the same factories.

In message , "Dave Plowman (News)" writes

Good question!

I thought this too, and that a standard battery would be overcharged by the Smartcharge system.

David

Very good point - the the charging voltage is calculated by the ECU according to battery temperature which is determined from engine air inlet temp when the car was last switched off, and what it is 'now'.

A Silver calcium battery charges best with a high voltage when its cold. Thus the ecu 95% charges it when its cold with upto 16v. They dont charge very well when hot.

A standard lead acid battery is the opposite way around. They have a high resistance when cold so only charge fully with some warmth in them.

Thus a standard battery will never be charged properly by the Focus smart charge system.

So now you know.

Tim..

PS, to the OP, for the Smart Charge to work at all, there is a fuse in the engine fuse box which must be a good fit and have zero resistance.

Check Pin3 at the alternator against battery voltage. They must match! A dodgy connection at the fuse or pin3 will stop the system charging at all even though the warning lamp has gone out on the dash...

I would NOT recommend jump starting a COLD Focus with a flat battery, as the ecu will often command full charging (remember 16v + ) from another car especially with its engine *running*. I've seen zapped ecu's etc on the donor car as a result.

Tim.

Right.

Are you saying a calcium type has a constant resistance regardless of temperature? Or works in the opposite way to a standard one?

It sounds like someone at Ford had a bee in their bonnet.

It would be an incredibly bad piece of design that couldn't cope with such a minor overload.