High Volts or High Amps?

[blodger]

Yes those you have linked to will do the job and are akin to those I have used. They do not carry much current, upto 3 amps, but Gibbo could advise better, so I have had none fail from overheating. Yes, the stud-like diodes give only a 0.3v drop/lift but easier to mount on a heatsink. I have found (25A) diodes out of old alternator similar.

There are at least three boats based on the Macc that now have A127s with the said diodes, back to back one forward and one backward, fitted permanently. Each time I see them they say they are still doing their job. One reckoned their batts were knackered a couple of years ago, another a year ago, but they still have not replaced. The thirds's batts are knackered old lorry batts but the real problem is not running the engine enough; new batteries would be knackered .

ETA By the way, they are liveaboards doing engine running often merely for recharging and, the one that's made his batts do two more years took advice and invested in two solar panels for this year.

Edited September 24, 2012 by blodger

[smileypete]

Could use one of the diodes in these:

 

 

Look for something like KPBC5010 on Ebay.

 

cheers, Pete.

~smpt~

[Gibbo]

Could use one of the diodes in these:

 

 

Look for something like KPBC5010 on Ebay.

 

 

You need two anti-parallel diodes so you'd need to use one of the AC terminals as one contact then link the two DC terminals together and use them as the other contact.

[Dave Taylor]

You need two anti-parallel diodes so you'd need to use one of the AC terminals as one contact then link the two DC terminals together and use them as the other contact.

 

That looks a bit simpler for me to use, especially if the case can be bolted direct to chassis earth - Can it? 50 amp rating, so no worries with overheating, I guess. Blade terminals too - easy for a beginner like me to wire up.

 

Just proved to myself that it will do what I want, by doodling the circuit of a bridge rectifier! I don't know much, but can remember that!

 

 

Any other points to look out for?

 

Thanks, Pete & Gibbo, I'm getting there!

[Gibbo]

Yes, the metal plate is isolated on those.

[Dave Taylor]

Yes, the metal plate is isolated on those.

 

Good!

 

Edit: One more thought: Does the higher current rating of these diodes mean that the voltage drop across them will be much different from the expected 0.6 volts? If so, any idea of how much?

Edit (2): Just looked at your website again, and think the answer is plain: only 0.6 volt drop at low current. The field current will always be low compared to the rating of these diodes, so the voltage drop is likely to be about 0.6 volts (perhaps a little more) all the time. Think that's right!

Edited September 24, 2012 by Dave Taylor

[smileypete]

Good!

 

Edit: One more thought: Does the higher current rating of these diodes mean that the voltage drop across them will be much different from the expected 0.6 volts? If so, any idea of how much?

PDF linky:

 

http://www.cnelectr.net/diodes/pdf/kbpc50005.pdf

 

cheers, Pete.

~smpt~

Edited September 24, 2012 by smileypete

[Dave Taylor]

PDF linky:

 

http://www.cnelectr....f/kbpc50005.pdf

 

cheers, Pete.

~smpt~

 

You are a mine of information! Useful info - especially the first graph.

 

Edit: Now this is where I display more of my ignorance: If I were to connect to both AC terminals on one 'side' and to both DC terminals on the other, would it give me an intermediate voltage drop, say 0.3 volts? I know it would halve the resistance if they were resistors, but have no idea whether diodes do the same sort of thing?

 

If they would behave like that, it would give me a way of switching in increased charge voltages of 14.7 or 15.0 volts, as needed.

 

No problem if not, I just wondered!

Edited September 24, 2012 by Dave Taylor

[Gibbo]

You are a mine of information! Useful info - especially the first graph.

 

Edit: Now this is where I display more of my ignorance: If I were to connect to both AC terminals on one 'side' and to both DC terminals on the other, would it give me an intermediate voltage drop, say 0.3 volts? I know it would halve the resistance if they were resistors, but have no idea whether diodes do the same sort of thing?

 

If they would behave like that, it would give me a way of switching in increased charge voltages of 14.7 or 15.0 volts, as needed.

 

No problem if not, I just wondered!

 

No. Look at the graph again on Pete's link. It would just be like using the same diode at a lower current (because each half would be passing some). Once you get to low currents it doesn't make much difference.

[Dave Taylor]

No. Look at the graph again on Pete's link. It would just be like using the same diode at a lower current (because each half would be passing some). Once you get to low currents it doesn't make much difference.

 

Mmm . . . yes,I wondered about that. Never mind, it was worth asking!

 

Now I am looking at how to intercept the connection between the regulator and D+. I have opened the cover on the back of the alternator, and there is no obvious connection, as the whole thing is encased in plastic.

 

However, the Merlin AMS installation PDF (here ) identifies the FRONT brush on Iskra alternators as being negative. The REAR brush must therefore be positive, which is the connection we need to intercept, and there is a connection tag from the nearest brush coming to a small bolt facing me as I look at the opened alternator.

 

Am I right to assume that 'front' and 'rear' could be stated as 'pulley end' and 'non-pulley end' respectively? If so, this looks like the connection which I need to intercept.

 

To check this, I am thinking of using my pocket multimeter to test the resistance between this bolt and D+. Presumably, if this is the correct terminal, there should be zero resistance between them?

 

Just checking, I can't do any damage by testing with my multimeter like this, can I? Obviously, I don't want to make expensive mistakes.

 

I could post a photo if that would help.

 

Thanks again.

[blodger]

A photo will definately be of assistance

 

WARNING: The diode mod is not about circumventing the alternator's own controller as with a propriatery alternator controller by soldering into the brush connection parts but fooling the alternator's regulator about the voltage it is producing and sending to the battery, not quite battery sensing. So it does not mirror fitting say a Stirling or other controller.

[Dave Taylor]

A photo will definately be of assistance

 

WARNING: The diode mod is not about circumventing the alternator's own controller as with a propriatery alternator controller by soldering into the brush connection parts but fooling the alternator's regulator about the voltage it is producing and sending to the battery, not quite battery sensing. So it does not mirror fitting say a Stirling or other controller.

 

Right! Here's a photo:

 

 

Yes, I am aware of the different approaches, and only used the Merlin AMS instructions to help me locate the positive brush. But thanks for the warning!

 

Gibbo's diagram (here) shows the diode(s) inserted between the D+ terminal and the regulator. I think I have identified the terminal from the positive brush.

 

In the photo, D+ is the middle of the 3 terminals at the top. They are W , D+ , and B+ . B- is to the left. I am assuming that the round object to the right of the brushes is the regulator, and the C-shaped black assembly carries the connection from the positive brush to D+ as well as the various diodes rectifying the stator outputs. (?)

 

What I think is the positive brush connection is the small slotted bolt head immediately to the right and below the brush assembly in the centre. It appears to feed straight out from the brush, but I cannot see whether that feed out is only going to D+, with an invisible (and separate) connection to the regulator, or whether there is another connection to the regulator, 'after' this slotted bolt. If there is, and I insert the diode(s) here, they will be not only between the D+ and the regulator, but also between the regulator and the brush. On Gibbo's diagram, that would be in the purple wire immediately above the brushes and below the branch off to the regulator. I don't know enough to know whether inserting the diodes here would work, rather think not.

 

It is difficult to see what more I can undo to reveal more potential connections. Perhaps the brush/regulator assembly, secured by the two posidrives? The whole C-shaped black assembly has several soldered connections to the stator coils, and I cannot see how any of it can be removed without unsoldering those - which I am NOT going to do!

 

I have a pocket multimeter. Are there any tests I can do to check whether the small slotted bolt would be the right place to insert the diodes?

[blodger]

Yes, I would remove the regulator/brush assembly by removing the two securing bolts and the terminal connection bolt.

 

On a Bosch hidden beneath there is a press contact terminal to the regulator from D+ which has to be intercepted with the diodes to mod it.

 

With the regulator out you will be better able to see any discernable feed from D+ to the regulator. The slotted bolt tou are suspecting because its all you can see would seem to be oriented wrongly for the purpose.

 

If you can locate pictures of replacement regulators some will attribure D+ to the relevant contact on it.

 

I do not think you can do any harm with your multimeter and the 9v battery in it but you may find continuity tests misleading and confusing because of the various pathways.

 

I think you will find that folk back off trying to be helpful for fear you end up damaging your alt and get upset at the encouragement.

 

I have modified cheap alts off EBay or known quantities like A127s. You will have noted from Gibbo/SG that not all alts lend themselves to be easily modded.

 

I just thought I had better give the health warning and add something from my own experience.

 

I helped out a liveaboard getting a starter motor running and fitting a working Bosch alternator from a scrapyard. I modded it so as to get the utmost charge on the rare occasions he can be encouraged to charge his batts. The alternator only lasted two years and the mod was probably partly responsible for working the alt hard and it getting hot. I have replaced it with an A127 I have repaired similarly modded.

 

ETA In your picture the cylindrical diodes are probably the D+ diode triac or whatever it is called. My alternator manual is on the boat but only covers oldish models.

Edited September 26, 2012 by blodger

[Dave Taylor]

Thanks for your reply, blodger. I'll insert my comments in blue next to yours:

Yes, I would remove the regulator/brush assembly by removing the two securing bolts and the terminal connection bolt.

 

Done that. Connection underneath to case/B-. Only other connection is the small terminal with the slotted bolt.

 

On a Bosch hidden beneath there is a press contact terminal to the regulator from D+ which has to be intercepted with the diodes to mod it.

 

From what I can glean from the Merlin AMS instructions I referred to earlier, Bosch and Iskra brushes are reverse way round from each other. In other words, on the Bosch the negative brush is to the rear (top as I look at it) and on the Iskra the negative brush is to the front (bottom). As I am looking for the positive brush, connected to D+, this will be the rear (top). Checked this by testing continuity between positive brush and the small terminal. Zero resistance between them.

 

With the regulator out you will be better able to see any discernable feed from D+ to the regulator. The slotted bolt you are suspecting because its all you can see would seem to be oriented wrongly for the purpose.

 

Thanks for the tip to remove the regulator / brush assembly. It has enabled me to really clarify the position.

If you can locate pictures of replacement regulators some will attribure D+ to the relevant contact on it.

 

I do not think you can do any harm with your multimeter and the 9v battery in it but you may find continuity tests misleading and confusing because of the various pathways.

 

Fine! I have tested between small terminal and D+ (with reg/brushes removed) - zero resistance. Between 'case' connection under brushes and B-, also zero.

Also tested the regulator, and find one of its 3 terminals continuous with small terminal, one with case connection (i.e. B-).

I think you will find that folk back off trying to be helpful for fear you end up damaging your alt and get upset at the encouragement.

 

Very understandable! I know that I am doing this at my own risk, and it is important that I satisfy myself that I have identified the correct connections. What has been very useful has been to pick the brains of folk like yourself, smileyPete and Gibbo. None of you have told me what to do, but you have kindly pointed me along the way to discover my own conclusions.

I have modified cheap alts off EBay or known quantities like A127s. You will have noted from Gibbo/SG that not all alts lend themselves to be easily modded.

 

Yes, all through this discussion I have been aware that at any time I might find myself up against a brick wall, unable to 'mod' my alternator, either because of its construction or because of my lack of knowledge / skill / courage !

 

I just thought I had better give the health warning and add something from my own experience. Thanks. Much appreciated!

 

I helped out a liveaboard getting a starter motor running and fitting a working Bosch alternator from a scrapyard. I modded it so as to get the utmost charge on the rare occasions he can be encouraged to charge his batts. The alternator only lasted two years and the mod was probably partly responsible for working the alt hard and it getting hot. I have replaced it with an A127 I have repaired similarly modded.

 

ETA In your picture the cylindrical diodes are probably the D+ diode triac or whatever it is called. Reckon you're right. One end of each of these is continuous with D+.

 

My alternator manual is on the boat but only covers oldish models.

 

To sum up:- As far as I can tell, the brush / regulator assembly on an N-type, negative ground alternator has only 2 external connections, D+ and B-. Having satisfied myself that there is a clear connection to B- and that there are no other connections, the small terminal should therefore be to D+. No other option, as far as I can see!

 

I shall now go ahead and buy the appropriate hardware, i.e. a bridge rectifier and a relay, plus some appropriately-gauged wire and connectors. I shall most likely go a little quiet for a while until I have got all these and done the modifications, but I shall come back and update the thread when I have finished - hopefully with success!

 

Once again, Many Thanks to all who have offered their help on this one.

Dave

[blodger]

Thanks for your reply, blodger. I'll insert my comments in blue next to yours:

 

 

To sum up:- As far as I can tell, the brush / regulator assembly on an N-type, negative ground alternator has only 2 external connections, D+ and B-. Having satisfied myself that there is a clear connection to B- and that there are no other connections, the small terminal should therefore be to D+. No other option, as far as I can see!

 

I shall now go ahead and buy the appropriate hardware, i.e. a bridge rectifier and a relay, plus some appropriately-gauged wire and connectors. I shall most likely go a little quiet for a while until I have got all these and done the modifications, but I shall come back and update the thread when I have finished - hopefully with success!

 

Once again, Many Thanks to all who have offered their help on this one.

Dave

I guess you know enough to proceed with caution so good luck. I am sure that if any of the experts have any concerns they will post sooner or later.

[Dave Taylor]

PROJECT REPORT

 

Well it has only been a month since the last post on this subject !!!

 

Sorry for the long delay in reporting back. I have been plagued with one 'supplier' in particular not delivering what I have paid for – just a simple relay, but I wanted to fit it alongside the two diodes so that I could switch off the voltage enhancement.

 

The little KBPC5010 bridge rectifier seems ideal for the job, connected as recommended. Within a short while, the charge voltage rose above the previous maximum of 14.4 volts and gradually crept up to 14.8. At this point, the relay is activated (initially manually by me, soon to be automatically by SmartGauge) to avoid possible damage to items connected to the batteries.

 

The D+ connection to the brush/regulator assembly within the Iskra alternator was the small terminal which I had identified, so I have been able to intercept that connection, bending the tag on the brush/regulator and inserting insulation to prevent shorting. The fact that it is a bolted connection has made inserting the diode circuit relatively easy.

 

So far, then, very successful and worthwhile. I look forward to my leisure batteries being better charged, with the benefit of a frequent 'mild equalisation charge' after nearly 2 months of just being charged at 14.4 volts or less.

 

Thanks again!

[Gibbo]

Amazing what can be achieved with a bit of bodgery!

[Dave Taylor]

Amazing what can be achieved with a bit of bodgery!

 

. . . which I would not have even known about without your very informative website, along with the supportive help from you and all the others who chipped in their ha'porth.