# Voltage regulator

#### Vento85

Joined Nov 2, 2011
4
Hi,

I would like some help with designing a voltage regulator. I am not very good at electronics as my background is in Mechanical.

But what I would like to do is:

Design a Voltage Regulator that can output a voltage of around ≈13.5v DC

The input voltage is from ≈13.4v to 16.4v DC (continuity changes between that voltage range)

The Ah ≈ 90Ah to 150Ah
(not 100% sure on this. (so should the circuit be designed to handle 150Ah even is the Ah turn out to be 90Ah in the end?)

Thanks

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#### SgtWookie

Joined Jul 17, 2007
22,221
What is supplying the voltage?

You are saying Ah; but that is a battery rating. Do you mean Amperes?

90A to 150A is quite a bit of current.

What are you going to do with all that current?

#### Vento85

Joined Nov 2, 2011
4
The supply is coming from a alternator of a car. The regulator is not working working so well.

I am currently out of the country (UK) with my car and dont have time or the tools to replace the alternator and its too expensive here to get a garge to do it.

The current alternator is rated about 90Ah or 150Ah so im not sure on the amps.

The battery is a 12V @ 62Ah.

If I am correct the output from a alternator should be 13.5v up ro 14.2v. But constant. I need to be about the make my voltage constant. Otherwise the head lamps Dim up and down.

Thanks

#### crutschow

Joined Mar 14, 2008
27,011
As S.W. said, Ah (Ampere-hour) is a battery rating, not an alternator rating. A typical small alternator output rating is 30-35A.

But you do not want to brute-force regulate the DC voltage, since that would require a huge linear regulator. You either need a new regulator for the alternator or, if the regulator is built into the alternator, a new alternator.

Besides, designing, building, and installing such a linear regulator would be far more work and expense than replacing the regulator and/or alternator, which is generally fairly easy to do.

#### SgtWookie

Joined Jul 17, 2007
22,221
I'm in agreement with Carl's reply.

Alternator output has increased over time; in the "good old days" when generators were used instead of alternators, the output might have been in the 20A-35A range. Alternators started out somewhere in the vicinity of 35A, and the largest automotive alternator that I know of nowadays is 130A.

It would be very difficult and expensive to try to regulate the output power of the alternator. The regulator controls the alternator output by monitoring it, and changing the amount of current that is fed to the winding in the rotor. The current in the rotor winding is multiplied by the mechanical force that is rotating it, and the power output from the 3-phase "wye" stator is fed through a 3-phase full bridge rectifier.

It does sound like your regulator is faulty. If your vehicle is quite old and the regulator is an external electro-mechanical one, you may be able to polish up the contact points inside using some very fine grit wet-or-dry sandpaper (NOT emery cloth, garnet nor flint paper) or an "ignition points file".

If it is a semiconductor regulator, you will have to purchase a replacement. That will be your least expensive and least troublesome route.

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#### bountyhunter

Joined Sep 7, 2009
2,512
It would be very difficult and expensive to try to regulate the output power of the alternator. The regulator controls the alternator output by monitoring it, and changing the amount of current that is fed to the winding in the rotor.
The alternator has two windings: the rotor and the stator. In most car regulators, they use a N-type FET or transistor to sink current to ground through the rotor (lower current) winding and that in turn controls the larger current flowing in the stator windings which can be upwards of 100A.

#### Vento85

Joined Nov 2, 2011
4
Yes it would be easier on some cars, but not on all cars to replace the alternator.

For me I would just replace the alternator once I get back to the UK.

To replace the alternator on my car is difficult and even more difficult without the correct tools on hand.

To replace the alternator on the car there are 3 ways to do it:
1, To remove the Power Steering pump
2, Remove the AC and Coolent Rads
3, Drop the engine out.

I plan to remove the Power steering pump once im back in the UK far easier.

Its a 2L engine thats why there is no room to work and due to the fact the engine bay is very compact.

Also its a diesel and so the alternator have a higher kick and bigger battery compared to a Petrol. There are 2 version of alternator for my car and they say are rated at 90 and 150.

I only plan to do it as A quick fix nothing permant.

I was thinking to use the +V output from the alaternator and regulate that out put directly.

Cheers

#### SgtWookie

Joined Jul 17, 2007
22,221
The alternator has two windings: the rotor and the stator. In most car regulators, they use a N-type FET or transistor to sink current to ground through the rotor (lower current) winding and that in turn controls the larger current flowing in the stator windings which can be upwards of 100A.
Yes, I forgot to mention the stator windings feeding the 3-phase bridge; I added that detail.

#### SgtWookie

Joined Jul 17, 2007
22,221
Vento85,
I'm very sorry about the bad news, but your only real option as far as a faulty regulator is concerned is to repair/rebuild or replace the alternator - unless the regulator is external; then it may be possible to replace just the regulator.

There MAY be another couple of issues involved:
Your positive battery cable may have rubbed its' insulation away on something like the shock tower, exhaust manifold, etc - and it is intermittently getting shorted to the chassis. This can cause very poor regulation like you have been seeing. This very thing happened to my 1965 Ford Mustang back in 1972; the positive battery cable had rubbed the insulation off and the cable was shorting out against the shock absorber tower when I was accelerating rapidly. The headlamps would come on VERY bright as long as I had my foot down - until the headlamps burned out due to the excessive voltage.

The other item could be a bad earth/ground wire from either the battery negative terminal to the chassis, or the engine block to the firewall. Some makes/models have the chassis ground from the negative terminal to the chassis near the battery; that ground/earth connection can be corroded at either end, causing an electrical fault. Almost all older US-makes had a ground strap from the engine block to the firewall; it sometimes happened that a mechanic would disconnect it during a repair, and forget to reconnect it.

Intermittent problems can be very difficult to diagnose.

#### Vento85

Joined Nov 2, 2011
4
I have checked all the wires and they are ok.

The regulator is built into the alternator. If it wasnt build in it would be very easy fix.

The grounds are good I checked them out all so.

#### crutschow

Joined Mar 14, 2008
27,011
I had a problem with an alternator not charging properly so I went to change the alternator. In the process I noticed that the V-belt V surfaces were rather shiny. I then realized that the problem was the belt had been too loose at one point and the belt was slipping which overheated the belt and caused it to glaze. That made it slip even when the belt was then at normal tension.

Moral: If the generator is driven by a V-belt, make sure it's ok and the tension is correct.