Resistors in charging circuit?

[davel]

Iona has a 50w resistor and also a 32amp fuse link in line from the alternator to each battery bank.

 

I want to upgrade the alternator from the existing 45 amp unit to a 100 amp unit and change the wiring so the output from the alternator takes a more direct route to the batteries.

 

Are the resistors and fuse links essential or can I do away with them?

 

Resistors.

 

 

Fuse Links above and to the right of resistors.

 

Cheers

 

Dave

[MoominPapa]

Iona has a 50w resistor and also a 32amp fuse link in line from the alternator to each battery bank.

 

I want to upgrade the alternator from the existing 45 amp unit to a 100 amp unit and change the wiring so the output from the alternator takes a more direct route to the batteries.

 

Are the resistors and fuse links essential or can I do away with them?

 

Resistors.

 

 

Fuse Links above and to the right of resistors.

 

Cheers

 

Dave

 

It looks like there are some big diodes in there too, above each resistor. They could be Zeners for voltage regulation. It looks like a rather strange arrangement: can you trace the actual circuit?

 

MP.

[WotEver]

The resistors are almost certainly the shunts for the ammeters. Up-rating the alternator might mean you need beefier shunts.

 

As for the fuses, I'd say remove them. BSS however says you need them (I believe).

 

Tony

 

Yes, those do look like diodes above the resistors, which is odd.

[Gibbo]

The resistors are almost certainly the shunts for the ammeters. Up-rating the alternator might mean you need beefier shunts.

 

Agreed. It looks like the two pairs of smaller black and red wires are directly across the resistors so probably go to the ammeters.

 

I'd suspect the diodes are zeners as someone's idea of spike protection to protect the alternators if the fuses pop or someone switches the isolators off.

 

The resistors are 0.01 Ohm 50W so 70 amp alternators would take them right to the limit assuming an infinite heatsink. With a small heatsink like that, and allowing a bit of a safety margin, I'd say 30 amp alternators would be about the maximum safe limit.

 

So yes, they need to be removed if the alternators are being upgraded.

[WotEver]

The resistors are 0.01 Ohm 50W

You've got better eyes than me sir. Or better glasses. Or a higher resolution monitor.

 

I squinted at them for ages and couldn't see any more than 50W.

 

Tony

[Gibbo]

You've got better eyes than me sir.

 

Doubtful after spending 25 years working on components the size of ant shit.

 

Or better glasses. Or a higher resolution monitor.

 

More likely.

 

I squinted at them for ages and couldn't see any more than 50W.

 

Look at the one on the right, I can see R01 = 0R01 = 0.01R = 0.01 Ohm.

 

They use an "R" or "K" or "M" instead of a decimal point so it can't get misread as a result of a single point getting worn off. They do the same on most schematics so a dot dissappearing on a photocopy doesn't result in someone putting a component in 10 (or whatever) times different in value.

[WotEver]

They use an "R" or "K" or "M" instead of a decimal point so it can't get misread as a result of a single point getting worn off. They do the same on most schematics so a dot dissappearing on a photocopy doesn't result in someone putting a component in 10 (or whatever) times different in value.

Oh yeah, I know that. I've been typing it that way for many many years. Never worked out why they don't do the same for caps - uF1 instead of 0.1uF (or 100nF)

 

(Or 100,000pF)

 

I just changed my glasses and clicked on the image to see it full res and now I can read it: 50W R01 +/-10%

 

Tony

Edited March 7, 2011 by WotEver

[Gibbo]

Never worked out why they don't do the same for caps - uF1 instead of 0.1uF (or 100nF)

 

Caps are a law unto themselves. Always have been. I have some 470pF ceramics here. Written on them it says "53" and that's it.

 

I just changed my glasses and clicked on the image to see it full res and now I can read it: 50W R01 +/-10%

 

So you could have actually saved me all that typing?

[WotEver]

Caps are a law unto themselves. Always have been. I have some 470pF ceramics here. Written on them it says "53" and that's it.

Ahh yes, the 53's

 

I never understood those ceramics that were popular in the 70's that looked like multi-striped smarties. The colour coding never made much sense to me.

 

So you could have actually saved me all that typing?

You know it's good for the finger joints.

 

Tony

[Gibbo]

I never understood those ceramics that were popular in the 70's that looked like multi-striped smarties. The colour coding never made much sense to me.

 

It's not just me then! Thankfully they're a thing of the past and I don't have to think about them anymore. Horrible things.

[davel]

It looks like there are some big diodes in there too, above each resistor. They could be Zeners for voltage regulation. It looks like a rather strange arrangement: can you trace the actual circuit?

 

 

MP.

 

I thought that was the mounting bolt, what a dolt.

 

 

Agreed. It looks like the two pairs of smaller black and red wires are directly across the resistors so probably go to the ammeters.

 

 

The output from the alternator goes to left hand fuse link on the 2nd photo then to the ammeter in the foreground then to the terminal in between the resistors.

 

 

I'd suspect the diodes are zeners as someone's idea of spike protection to protect the alternators if the fuses pop or someone switches the isolators off.

 

 

Your wording suggests this is not an effective method of spike protection or not needed.?

 

 

The resistors are 0.01 Ohm 50W so 70 amp alternators would take them right to the limit assuming an infinite heatsink. With a small heatsink like that, and allowing a bit of a safety margin, I'd say 30 amp alternators would be about the maximum safe limit.

 

So yes, they need to be removed if the alternators are being upgraded.

 

 

Presumably removed if I got rid of the ammeter, upgraded if I wanted to keep an ammeter.

 

 

 

 

I have started a diagram of the wiring. How do you post a document?

[WotEver]

I have started a diagram of the wiring. How do you post a document?

http://www.canalworld.net/forums/index.php?showtopic=1633

 

Tony

 

Presumably removed if I got rid of the ammeter, upgraded if I wanted to keep an ammeter.

Yep.

 

Tony

 

Your wording suggests this is not an effective method of spike protection or not needed.?

It might work, and its better than nothing.

[alan_fincher]

 

If those resistors are ammeter shunts, and are +/- 10%, then, unless the ammeter has some further calibration, presumably it's reading could be out by the same kind of percentages as the tolerance in the resistor ?

 

Aren't shunts usually fairly accurate resistors ?

[WotEver]

 

If those resistors are ammeter shunts, and are +/- 10%, then, unless the ammeter has some further calibration, presumably it's reading could be out by the same kind of percentages as the tolerance in the resistor ?

 

Aren't shunts usually fairly accurate resistors ?

Yes, and... yes.

 

Someone did it on the cheap.

 

Tony

 

Having said that, 10% ain't really that important on charging current. The difference between the batts taking 30A or 33A isn't particularly relevant, is it? Likewise, 1.5A or 1.65A.

[Semitrad]

Caps are a law unto themselves. Always have been. I have some 470pF ceramics here. Written on them it says "53" and that's it.

 

 

Sure they're not 4,700pf? (Pedant hat on)

 

My take on the diodes is that they would protect the meter circuit if the shunt resistor went o/c by shorting out and blowing the fuse (and possibly becoming a piece of wire in the process).

[Gibbo]

Sure they're not 4,700pf? (Pedant hat on)

 

Definitely 470pF. If I'd measured 4,700pF then I would have guessed they were supposed to be 5,000pF (and very old) in which case 53 would make sense. I often wonder whether caps have random numbers stamped on them just for a laugh?

 

My take on the diodes is that they would protect the meter circuit if the shunt resistor went o/c by shorting out and blowing the fuse (and possibly becoming a piece of wire in the process).

 

That's a possibilty, but it's an odd way of doing it considering a 1/4 watt series resistor to the voltmeter (which is being used as an ammeter) and a 1/4 watt zener would have done the same thing.

 

Having said that, 10% ain't really that important on charging current. The difference between the batts taking 30A or 33A isn't particularly relevant, is it? Likewise, 1.5A or 1.65A.

 

Totally agree. For general use even a 20% error is often perfectly acceptable for current measurements. Accurate current measurements are only really needed for design, they have very little use otherwise in a normal boat. As long as the owner knows. What is important is repeatability. If it measures (say) 20 amps at 15 amps, as long it always does that all is fine.

[Chalky]

Are the diodes someones idea of a split charge diode on the cheap? They're fairly small diodes (if your used to 500A ones), but they may take 20 or 30 A each. Is there anything written on the sides of them?

 

Second thought - it doesn't look like its wired as a split charge but if they're there for transient suppression they probably blew years ago - they're tiny.

 

They've also been soldered, so there's a potential failure mode there due to vibration causing stress fractures.

Edited March 7, 2011 by Chalky

[WotEver]

Are the diodes someones idea of a split charge diode on the cheap?

Nope, can't see that. Firstly, they're reverse biased; secondly, OP already has two alternators; thirdly, the black wire coming from the cathode/heat sink appears to go to a meter case.

 

Tony

[Gibbo]

Nope, can't see that. Firstly, they're reverse biased; secondly, OP already has two alternators; thirdly, the black wire coming from the cathode/heat sink appears to go to a meter case.

 

Split charge diodes in the negative!

 

It's no more stupid than putting isolator switches there

 

Chalky did go on to say

 

Second thought - it doesn't look like its wired as a split charge...

[WotEver]

Split charge diodes in the negative!

Of course. Stupid of me not to realise.

 

Tony

[Chalky]

Nope, can't see that. Firstly, they're reverse biased; secondly, OP already has two alternators; thirdly, the black wire coming from the cathode/heat sink appears to go to a meter case.

 

Tony

Not all stud mounted diodes are configured the same, so it is possible. Also having seen the installation I didn't assume that the black wire was necessarily the -ve - I've seen some very odd wiring in my time!

[Gibbo]

Re-reading the entire thread carefully, and looking closely at the photos, I'm beginning think it actually is a pair of split charge diodes.

[WotEver]

Re-reading the entire thread carefully, and looking closely at the photos, I'm beginning think it actually is a pair of split charge diodes.

So the alternator output is coming in on that black wire?

 

Tony

 

And I've re-read the thread myself and just realised that OP said nothing about twin alternators. In fact, quite the opposite. So I apologise - I don't know where I got that from.

[Gibbo]

So the alternator output is coming in on that black wire?

 

Alternator to left hand fuse, then to ammeter, then black wire to centre of that panel, then through the two diodes. Exactly what all the other wires and shunts are for is a mystery to me.

 

And I've re-read the thread myself and just realised that OP said nothing about twin alternators. In fact, quite the opposite. So I apologise - I don't know where I got that from.

 

Same place I got it from? Imagination?

 

I'll be honest, I'd rip the lot out and start again.

[Chalky]

 

I'll be honest, I'd rip the lot out and start again.

 

The wiring is stranded, but not multi-stranded, so is liable to vibration fracture. It uses domestic fuse holders (top of picture), and block connector. I agree with Gibbo - I'd be seriously considering a re-wire.

 

Look at the second photo. The black wire comes from the diode circuit to something that looks like an ammeter? From there a red wire goes to one of the fuse holders at the top of the picture. It's a split charge diode, with wiring that contravenes the regulations. Re-wire time.

Edited March 9, 2011 by Chalky