Alternator symptoms – what do they mean?

Bit vague but if you are saying that once the engine fires, the volts are high for 45 seconds then drop to normal?

If so then that's the alternator bunging in some charge to replenish that lost by starting.

Toyotas are fitted with a temperature controlled alternator, it will start charging around 14.4V on a cold day and gradually reduce as the engine bay warms up.

If you start the car and run the engine at around 1500RPM it should go to the normal charge voltage within a few seconds depending on the load, ie glow plugs will hold it down for awhile as will the main and auxiliary batteries if they a low.

A rough test of the alternator is to let the motor warm up, then turn on the high beams are conditioner on high, rear screen heater etc, run the motor at 1500 RPM and it should be able to hold the charge voltage at a reasonable value.

Indro Cruiser
My comment is similar to HBK. Your engine is a direct injection engine and some form of intake heater system. this system works when cold enough and switches on a heater load, be it glowplugs in some models and usually a thin W shaped vane in direct injection engines. When you start, it should start immediately with almost NO cranking time if the ambient temp temp of air is sufficient to cause ignition heat when fuel is injected into the cylinder. Only if too cold will the intake heat system activate and provide additional air heat to cylinders, sometimes thos is a two stage unit. Little heat or lots of heat and proportionate battery current drain. Therefore there may be varying amounts of alternator charge recovery time happening depending on ambient start temps. Because the normal hot start is almost instant the actual load on the battery is normal but very brief and requires almost no recovery charge time and so battery voltage will rise quickly.
If O C Day then probably the full heater current is flattening the battery AND then a starter load as well. That style of start means far more to replace into the battery and charge current and relatively low voltage of alt output which reduces in stages as the heater loads are switched off by the cold start controller. I had a HJ61 direct Inj engine for 25 years and when very cold, both intake heaters would activate and hold the alt voltage when running at around 12.4, then over 13v when one switched off and then a rise to around normal when the loads were gone. If cold around 4 min with the std OE 100 amp alternator, the high but not long run of heaters and starter were replaced quite soon. Yours should behave in a similar manner seeing it very similar in all respects.
If you are measuring a return to normal in 45 sec then only the starter current load is being replaced and is normal operation.

You have to have enough revs/min to enable the alt to make electrical charge current but once past a certain speed of rotation increasing revs does absolutely nothing as it is the regulator which is governing alternator rotor field strength of magnetism and appropriate charge into the battery according to battery state of charge at that time. The suitable revs is governed by the pulley sizes driving the alternator and is factory determined as being suitable, all are like that.

What you are seeing is Characteristics NOT Symptoms, bit of a difference there.
Relax,, Cheers.

Pretty much the same for me.
The voltage(dash guage) appears low/uncharging until you move off.
I'm on my second alt, on a 2005 100 series and both alts are/were the same.
I generally don't move of until the oil psi has maxed out which means most folk wouldn't even notice.

Thank you RMD for a very clear and full explanation of the characteristics of the system. Much appreciated. I am now reassured, my education is improved and I will hold back my paranoia! It also explains why I do not see any delay when the hot engine is started and very little intake heating is required, if any, and voltmeter then almost immediately shows higher that 14 volts.

Given the lead from RMD, I have now found further details at Page 26 and Page 40 of the document “1HD-FTE Engine Specifications/Improvements” found at http://www.lcool.org/forum/viewtopic.php?t=15031. It is included here in case it is of interest to others.

My vehicle easily passes the rough test prescribed by HKB.

The observations of Malcolm M and 2208mate also are appreciated.

John P.

Indro / John
Re reading your earlier post it seems the brushes gave up their contact on the rotor slip rings seeing the issue suddenly began. That would stop all output, If it lasted 190K = km's then the electricals were reliable. You were taking readings of the new alternator and so a few more comments. If the brushes don't contact then output stops, but sometimes a diode can blow and become shorted. That usually discharges the battery when stopped. If a diode goes open circuit, then the alternator loses 2/3 of it's output amp ability BUT will still make normal voltage to the battery while supplying a few amps for the system. However, if the vehicle has to charge other batteries or there is higher electrical load then the battery voltage will slowly drop even though the engine is running. A blown diode usually makes the alternator "growl" as revs rise a bit above idle. This can also be detected by listening to the alt or via a hose to alt case and ear. Sometimes, noise in radio system too. Alternators having to charge more than one battery system or feeding to a DCDC unit require higher rotor current for much of their life and so brushes WILL gradually wear/burn shorter at a faster rate than normal. As stated, many people carry spare brushes for that reason.

RMD is on the money, when the engine starts, all the alternator output goes to the intake heater and the rest of the electrical system is isolated from it, supplied by the battery, after about 45 secs, usually, the alternator switches from the heater to the electrical system, even on a warm day this usually occurrs.
I found this out when I fitted an ammeter on the alternator output, idle after start is about 60 amps and with a few revs goes over 100, with the battery voltage remaining around 12 volts or lower, then it switches over and the battery quickly rises to around 14 volts.
It had me baffled too at first till I looked into it.

I was told years ago, that when starting a Diesel engine, you should turn the ignition on and wait for a few seconds before starting to allow the pre heating system to actually pre heat. Not sure if this still applies in modern Diesel engines, but it is what I do, wether the engine is hot or cold. I can’t say I have noticed any change in battery voltage on the dash gauge. I have not put a multi metre on the battery to confirm.

Macca.