Alternator mystery

[ANDYD]

Hi have a new Lester 12v alternator (according to the label) that gives out 28 volts?

I wondering if there is a mod or a wire link that is missing to bring the output down to 14 volts or does this new alternator just have the wrong label???

Any thoughts?

cheers
Andy

[mepham55]

Doesn’t sound right. Never heard of a Lester alternator?Matt truck is this for? A Delco 10si is the go to alternator for series trucks; easy and cheap.

Matt

[landcrabmechanic]

Sounds like you have a rectifier issue, or whoever wound the alternator screwed up and able it wrong.
It looks like it is internally regulated, you could always see if there is an external regulator you could use.
I would suggest taking it back to where you got it from or an auto electric shop to have it repaired properly.

[ANDYD]

Thanks for the replies. The previous owner of the vehicle had purchased it (from who knows where!) so there is no return option.
It is brand new so I hooked it up on the engine and (thankfully) tested the output before connecting to my 12v battery :shock:

According to what little info I could find on the internet they are used on tractors! Maybe I will take it into Brighouse Auto to see what they make of it.

[red90]

It is brand new so I hooked it up on the engine and (thankfully) tested the output before connecting to my 12v battery :shock:

How can you test it without hooking it to a battery? The regulator can't work if it is disconnected.

[bsa_m21]

FYI - If the alternator has permanent magnets, it will produce power without a battery.

The Lester alternator you have is the equivalent to a Delco 10SI. (https://www.nationsstarteralternator.co ... -102-1.htm)

The alternator may be fine. The second you disconnect a battery (or don't have one connected), the voltage regulator tells the alternator to put out maximum power. With no battery in the circuit to act as a capacitor, some alternators can put out up to 50 or 60 volts, depending on engine RPM's. Still, to be safe, take it to any auto electric shop and ask them to test it for you.

[ANDYD]

Hi John & Martin, thanks for the replies and information.

So what you are suggesting is testing while disconnected from the battery the 24 volt reading is normal, but once its connected to the battery it will only read / give my battery 14 volts?

Thanks for the link,

Cheers
Andy

[red90]

As I understand it the voltage regulator needs somewhere to send some current or it can’t control the voltage. You can also damage it by running it disconnected.

[bsa_m21]

Hi John & Martin, thanks for the replies and information.

So what you are suggesting is testing while disconnected from the battery the 24 volt reading is normal, but once its connected to the battery it will only read / give my battery 14 volts?

Thanks for the link,

Cheers
Andy

Correct.

[ANDYD]

Just as a follow up to this, the alternator that was giving out 28v when not connected to the battery, is now giving out 14v when connected to the battery.

Thanks again for the tips, I learn something new everyday :drunken:

Cheers
Andy