Alternator Polarity

MarkJohnson12345

MarkJohnson12345

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www.markjohnsonafloat.org.uk
Am going to fit an Adverc system to the Sadler.

1st step is to be certain of the alternator polarity?

The Aletrnator is on an old Bukh 20, anm told is is probably a Marchal 35 amp.

Certainly produces that charge when battery is low.

How do I check the polarity??

Mj
 
If the existing system is working, first check your multimeter across the battery,
Then measure from the engine block to the battery -ve should be 0v, and the battery +ve, should be 12pointsomething volts.
Or you can trace the negative cable from the battery to the block, or measure between the alternator output and the block.
 
Older SEV-Marchal alternators tended to be positive polarity. Best solution would be to get the alternator make/model info and give it to Adverc, they'll decide which model to send you.

If you really want to do it yourself, get a multimeter on ohms x 1 scale and check the resistance between the field connection and the negative terminal - around 3-8 ohms is right for a positive polarity regulator. A negative polarity regulator will give you the same 3-8 ohms resistance between the field connection and the positive terminal.
 
Some confusion arising over the meaning of "alternator polarity"

lw395 interprets it as meaning is the output teminal the positve or the negative.

pvb interprets it as meaning is the alternator positive or negative regulated.
 
The poster wants to order an Adverc regulator. They come in 2 versions, positive or negative, according to the way the alternator's internal regulator is wired.
 
The question asked strictly speaking means Does the alternator produce +ve voltage at the output or -ve votlage at the out put. However as I am not aware of any alternator producing -ve output compared to ground then we assume that he is asking about the connection of the field coil to the regulator.

The field coil (the rotating coil) can have one side connected to the + output and the other side connected to -ve frame via the regulator.
The other option is to have one side of the field coil connected to gound -ve and the other side connected via the regulator to the +ve supply and or output.

So these 2 arrangements have been described as -ve or +ve regulated alternators. (inevitably shortened to + or -ve alternators.)

The field coil ios connected to the outside world via the brushes so to determine which type of regulation it is you can measure the resistance of each brush to ground and to output terminal.

good luck olewill
 
[ QUOTE ]
you can measure the resistance of each brush to ground and to output terminal.

[/ QUOTE ]

Not necessary. Just have to tell Adverc the model as pvb and the answer to FAQ 6 both say and they supply the correct item.
 
Yes, Thanks all for information.

As Vic says you can buy a positive or negative polartiy piece of kit, thus I need to know which my alternator is / does??

Being a whimp, I am afraid to take of the alternator (not broke don't fix it attitude) thus was hoping to be able to 'test it' in situ. The manufacturers name etc is well hidden.

Sounds though I am going to have to bite the bullet and take off the alternator to get a good look at the names on its rear end.

Thanks.

Mark J
 
According to the Book of the Bukh, the DV20s were fitted with in of 2 types of alternator:

Engine number: 93638 - 96232 had a SEV Marchal A 14/30, which had an SEV Marchal F 14V Voltage relay.

Engine number 96233 on were fitted with SEV Marchal 14/35A with a SEV Marchal T 14V voltage relay.

Earlier engines had a Dynastart.

Before investing in expensive control gear, consider that the SEV Marchal alternators are obsolete, spares difficult (sometimes impossible) to get, and may not be replaceable should it fail. I know, I had to spend a fortune on mine after spending several weeks tracking down spares which were wrong anyway. Would have been cheaper to start again, specially when it failed again a year later!
 
what an awful lot of fiddling around -

[ QUOTE ]
Yes, Thanks all for information.

As Vic says you can buy a positive or negative polarity piece of kit, thus I need to know which my alternator is / does??

Being a whimp, I am afraid to take of the alternator (not broke don't fix it attitude) thus was hoping to be able to 'test it' in situ. The manufacturers name etc is well hidden.

Sounds though I am going to have to bite the bullet and take off the alternator to get a good look at the names on its rear end.

Thanks.

Mark J

[/ QUOTE ]

The folks at Adverc are very nice and know their onions.
They are part of dying breed of British manufacturers who want to give customer satisfaction.
They are not particularly concerned whether or not you buy the product direct from them or no.

Give them a bell - the number's on the website. The lady who answers the 'phone (usually) is pretty jolly good technically, and most likely can answer your query herself.

I agree removing the alternator can be a pain, and dismantling it to get at the innards is very daunting - for the first time that you do it - then you realise it's no big deal, that is if you feel confident with spanners and Birmingham Screwdrivers.

Regardless of the above the alternator will have to come apart anyway to install the "field wire" to make the Adverc system work, they'll do that for you as a separate exercise, if you want - or any competent local alternator repairer, if you want to save the two way carriage.

Go on, ring them up, you know it makes sense.
 
Mark,

A point which does not seem to have been made is that whichever 'polarity' alternator it is, you will almost certainly need an internal connection to one or other of the brushes for the 'smart-regulator' anyway....so you will have to take the alternator off !

Determining the 'polarity' and making the connection is certainly not difficult, but I can understand that it is the sort of job many people won't contemplate.

For the record, the original alternator on my BUKH20 (1984) was a Paris-Rhone.....but that died after the first splash of bilge-water. (the diode matrix was on an unprotected printed circuit board). Since then I've used a car alternator from a scrap yard with absolutely no problems.

Vic
 
[ QUOTE ]
Sounds though I am going to have to bite the bullet and take off the alternator to get a good look at the names on its rear end.

[/ QUOTE ]
Mark, you don't need to remove the alternator to find out if is positive or negative output.

All you have to do is see which battery terminal is connected to the engine block. You don't even need to follow leads to do this.

All you have to do is use a DC volt meter or a continuity test lead or even "Mark One Eyeball".

If the Battery -ve terminal is connected to the engine block then your alternator is "Negative Earth"

If the +ve terminal is connected to the engine block then the alternator is "Positive Earth".

Easy really. /forums/images/graemlins/grin.gif
 
[ QUOTE ]
Mark, you don't need to remove the alternator to find out if is positive or negative output

[/ QUOTE ] it is not the polarity of the output. its whether it is positive or negative regulated.
Read the other posts in the topic!

It'll probably have to come off to connect the Adverc so the sensible thing to do is to take it off now and quote the model description to Adverc as they suggest.
 
Thanks all.

An alternative is the Sterling Alternator to Battry Charger.

Much easier to fit, but twice the price.

Some here are unhappy with Sterling company, and Adverc is much better thought of, if it makes any dfference!

I have spoken to a local engineer who would fit the system, and he recommends changing the old alternator for a new one at the same time.

As usual, a £200 job is begining to cost £400.

What I want is to be able to get the most amps for an hours charging whilst sitting in New Grimsby harbour when (if) summer arrives next year.
 
Before changing anything, how about finding some information ?

What voltage is your batteries getting to on charge ?

What voltage is the alternator running at on it's output terminal ?

What currant are you charging at ? CPC have a digital multimeter / clamp ammeter ( IN0487934 ) for £22.50 + VAT

Do you have split charge ?

What size batteries ?

You need a problem before you can repair it, have you ?

Brian
 
"As usual, a £200 job is begining to cost £400.

What I want is to be able to get the most amps for an hours charging whilst sitting in New Grimsby harbour when (if) summer arrives next year."

Expensive amps!

You will not get any more amps from a 35amp alternator simply by fitting pricy gadgets to it. If you really want to boost things, you need a more powerful alternator anyway.

FWIW I never had any charging problems using the standard 35a alt on my Bukh, it seemed to keep up with consumption while out cruising in spite of a fairly hungry Laptop, radio, and quite a lot of cabin lighting each evening.
 
[ QUOTE ]
Thanks all.

An alternative is the Sterling Alternator to Battry Charger.

Much easier to fit.





[/ QUOTE ]

I have just soldered two wires on to the brushes on my alternator (Bosch car type 90AHrs) to determine the polarity in order to fit a Sterling regulator.

I decided to remove the alternator to get easier access.

I made up a bench setup of of battery, alternator, ignition warning light and tha tacho to try and measure things away from the engine. But gave up when i realised that I had to turn the alternator at twice engine speed because of pully size.

So my measurement to determine which of the wires to use will be done with the engine running once I refit the alternator.

I quite like the ability to disable the boost function by breaking a single wire on the Sterling booster.

Iain
 
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