Prado 120 Diesel Alternator Voltage

your alternator is set at 13.8v - 14.5v and when under bonnet temps rise will fall back to +- 13v
some new fords go back to 12.7v when temps rise to an overheat level

Item number: 320531837221 E-bay boosts the alternator output for Prado

A general rule is that all 12V lead-acid batteries should be charged at a maximum of 14.4V (long-term) at normal temperatures. (With voltage dropping as temp increases - I think 0.1V per 10 degrees C, but I'd have to check....)
Once full, they are supposed to drop to 13.8V.

Someone once wrote that diesels charge at a lower voltage, but they never explained why...
But since a vehicle's electric system (voltage) is based on its battery and not its systems (if 12V or 24V etc), whether diesel or petrol shouldn't matter.

If you have a classic alternator (not the newer DP or ECU-controlled/interactive types), then....
Many trick their alternators into higher voltages by inserting diodes in their sensing line. Easily done if the alternator as an S = Sense wire (like 2-wire Bosch SL alternators, or Nippon Denso SIL 3-wire alternators, etc) and usually as easy if it is a 2-wire IL type. (S=Sense = direct to battery +12V; I = Ignition +12V which is usually the sense input if no "S" is present; L = the chargeLamp circuit).

Single-wire alternators (with D+ output for the chargelamp) cannot easily be tricked.

A typical diode has a forward voltage drop of 0.6V, hence if that could be inserted in to you sensing line, the voltage should go from 13.6V to 14.2V.
A 20c diode like a IN4004 should suffice (1A, 400V) but silicon diode of 1A or more rated at 50V (preferably 200V) or more should suffice.


There are other ways of trimming the voltage, but diodes are simple and reliable. (And there are diodes with 0.2V - 0.7V forward voltage drops.)

Talk to Derek at ABR. He just sorted my old mans prado out for him. Get a plug in voltage booster of ebay as previously mentioned. But have a chat to Derek Bester first.

Matt

Chris,
You'd want to be sure about what the charging voltage is before you embark on this path. Your alternator is temperature regulated - so the voltage drops when the alternator gets hot. Also, you may find your voltage drops a bit at idle.

Unless Toyota have changed the Prado alternators, I'd expect your voltage to be around 14.2 about 2 minutes after starting, and with the revs at about 2000rpm. 13.6V is what I'd expect in hot conditions.

Your AGM will charge at lower voltages - might take a bit longer. If you fit the Redarc, you will limit charging to 20amps. I use a clampmeter to measure current going into my batteries and after being used overnight, my AGM often takes 35-40amps at 2000rpm.

I wouldn't consider the diode option - too much at stake when you start delivering an extra 0.7 volts to all your vehicle's electronics.

This will be interesting!

......can't wait.