how to convert Positive Pole to Negative

z323791 · May 16, 2022

My PMA has three positive AC poles is there any device which I can use to convert either pole to negative
Thanks

littlespark · May 16, 2022

You might need to rephrase the question with the correct terminology, or you’re going to get strange answers.

An AC supply changes from positive to negative 50 times a second , (in UK) so are you asking how to change a line to neutral?

Saying you’re from the Moon also won’t help with answers

z323791 · May 17, 2022

littlespark said:
You might need to rephrase the question with the correct terminology, or you’re going to get strange answers.

An AC supply changes from positive to negative 50 times a second , (in UK) so are you asking how to change a line to neutral?

Saying you’re from the Moon also won’t help with answers

Yes, you understood correct my PMA (Alternator) has 3 AC +ve output A, B and C. to my understanding you need +ve and -ve to run appliances when the PMA moves I have to use Bridge which turns AC to DC and I get both +ve and -ve from three (A, B, C) poles but then I have to use a converter to get it back to AC.
I want to eliminate the converter and bridge from my circuit and would like to know if there is a device or circuit which I can use to get AC +ve and -ve straight from PMA output Poles
Thanks

pc1966 · May 17, 2022

Typically alternators are three phase, so they have 3 terminals that are all AC and spaced 120 deg in phase angle apart. The use of a suitable 6-diode bridge rectifier then results in a moderately smooth DC for charging batteries, etc.

If you use just two of them (any pair) you will get the usual single-phase AC (similar to a domestic outlet). However, by ignoring the 3rd one you are not going to be able to safely get as much power out without the risk of overheating the windings.

You have not said what the voltage is from the alternator, or what voltage you need for the load. A transformer will change the voltage, but you have other issues:

If the supply is not designed as a generator to substitute from the grid it may well have a very different frequency and that can cause problems. You cannot easily convert frequency, and the easy way is to do what you already do (covert to DC, back to fixed AC).
On a similar theme, the output voltage may not be regulated (and / or may depend on the DC output) so you can have problems of widely varying voltages.

TL;DR You need to provide more details.

pc1966 · May 17, 2022

The image here is a good illustration of a 3-phase bridge rectifier and how it gets smooth-ish DC from your style of alternator:

Six-pulse full-bridge rectifier: firing angle vs output voltage - Page 1

eevblog.com

Sapper · May 17, 2022

z323791 said:
Yes, you understood correct my PMA (Alternator) has 3 AC +ve output A, B and C. to my understanding you need +ve and -ve to run appliances when the PMA moves I have to use Bridge which turns AC to DC and I get both +ve and -ve from three (A, B, C) poles but then I have to use a converter to get it back to AC.
I want to eliminate the converter and bridge from my circuit and would like to know if there is a device or circuit which I can use to get AC +ve and -ve straight from PMA output Poles
Thanks

I suggest if you do find a way you should patent it then auction it to the highest bidder. IMHO
It's a fact that (due to phasing) L1+L2+L3=0V and a very hot alternator.