When I face an unknown alternator with a built-in regulator, the first things I do are:
- I hook up a voltmeter to the battery, start the engine and watch where the voltage levels off. That is the regulation voltage. Then I keep it running and watch if that voltage steps down after a while. Sometimes it does, sometimes not. If nothing has happened after 20-30 minutes at constant voltage, it will never happen.
- While doing the above, I also measure the voltage at the back of the alternator to get an idea of the voltage drop in the wiring. Do this early, while the alternator is still putting out full current. If I have a clamp meter available, I also measure the current. If you are losing significant voltage, the B+ and/or ground (B- if applicable) cabling is too small: replace it before doing anything else. It commonly is, because heavy cable is more expensive.
- I look for any hint that the alternator is externally sensed. In this case, there is a small wire going straight from the back of the unit to the battery, or sometimes to the starter motor/solenoid. Also, if the alternator output voltage is highest as the voltage reaches its limit and then drops a bit while the battery voltage stays constant, you can bet it is externally sensed.
- I look for any voltage adjustment pot on the back of the alternator, but those are rare/never found on automotive units.
- I look for any splitter and similar devices in the path of the charging current and measure any voltage drop there. It must be compensated for, through external sensing, or will result in poor performance.
Modern SLA batteries have an amazing ability to recombine gases without venting or losing water
and they tolerate relatively high sustained charging voltages. Some stock modern alternators found on marine
engines are precisely designed to operate with them and do a very decent job.
My experience is also that external regulators (with a special mention for the blue ones potted in silicone with cooling
fins) are remarkably prone to just-out-of-warranty failure, while the factory built-in ones are rather reliable. I avoid removing built-in regulators as much as possible, because they normally also offer some thermal protection.
Some built-in automotive regulators are quite hopeless, for example charging up to 14.3V for a few minutes and stepping back down to 13.8V
. When that happens, replacing the whole alternator with another model with better characteristics can be a cheaper and smarter move than a "smart regulator". If you know what you are looking for, second-hand alternators can often be had for very little.
A Mitsubishi A003TR0093ZT is a seriously marinised 14V/115A alternator that delivers 14.3V continuously, which is pretty good in normal temperatures and even better in the heat. It also has a built-in over-temperature thermostat as a last resort. It is found on all the new D-series Volvo
Internally sensed alternators can usually be modified to sense externally at little cost. The process varies a little from model to model. Adding a small diode in the sensing line of an alternator bumps the voltage up by 0.4-0.65V depending on the diode model.
Last but not least, I am yet to find a smart "smart regulator" on the market. Since they don't measure output current - ever - they have no idea of what the battery is doing. They just deliver a dumb profile based on voltage setpoints and an absorption time set by the owner and if it hurts the battery, well, "who actually configured that?" I hear them say...
Charge and go through the stages, stop the engine, restart it and watch them happily over-charge the battery.
Many "smart regulators" are set incredibly aggressively - not such a great idea.
This being said, external regulators can be useful and make life much easier at times. I walk away from any model that gets warm, i.e. features cooling fins etc. Considering the current they handle (field currents are typically 3 to 8A or so) there is no excuse for designing electronics
that run hot. This indicates that someone is saving money
on power transistors in there at the expense of reliability
and unit life, or the design itself is very poor.