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Alternator Output question


Ratkatcher

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Sorry to be picking your collective brains once more but...

The 'user manual' (can't remember the exact name and it is on the boat) for my Thorneycroft 90 (BMC 1.5) shows the wiring diagram associated with the marinised engine with the original alternator number crossed through and A133 written beside it. The thing is that the alternator looks nothing like all of the photos of the A133 I have looked at - more like an A127 - as it has a voltage regulator block at the top of the alternator.

From my reading the A133 output is 70'ish amps (or more) but this baby only delivers around 30 Amps on startup rapidly dropping to 20 or lower after a very short time - even when the domestic batteries (2x110 AH - only weeks old) are quite low (60% or less remaining) and voltage sits around 13.1 volts for a very long time before gradually creeping up to around 13.6 after four or five hours at the tiller.

I'll clean it up a bit and take a photo to post on Sunday for comments if anyone could help identify it - also perhaps advise on if I should replace it with something else...

That said - if anyone with more technical experience of matters electrical than me (that wouldn't be hard!) just happen to be on the Shroppie from Sunday I'll be heading off in the direction of Norbury Junction and would apreciate trading knowledge for an ice cold Guinness (or JD & Cola) and be an attentive student too!

Thanks to you all in advance.

That reminds me - I read a thread from someone asking if they had the same manual - if they read this before I find it please PM me and I'll hapily scan the manual and send it to them.

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The A127 alternator has a max output of about 70amp too. But if the volts output never exceeds that 13.6v after that length of time running then either there's a faulty connection, the alternators faulty, belts slipping, or you actually have an old ACR alternator on there which would have a max output of between 35amp and 45am and around 13.6v. A picture would be helpful.

Has the alternator got a big black plastic casing on the back, where the terminals are?

Edited by bizzard
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No black casing on the back, just a large voltage regulator at the top (black, almost quadrant shape) and the legend 12 as a sticker on the middle of the rear casing.  Cables are attached to bolt on terminals and not the 3 pin Lucas connector (which I think was common around that era) rev counter probably coming from it too.

I'll post a picture Sunday when I am back on the boat.

Thanks.

Edited by Ratkatcher
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I think your alternator is a the original A127 , 35/40 amps in normal use (Max) , max voltage depends off length of wires but never exceed 13,8 volt ,  but a picture says more .

a question : when switching on a few  domestic users : did the amps grow up to maximum ? Voltage drop ?

you wrote the batteries are a few weeks old , did you charge them full before replacing the old batteries ?

 

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As promised, a few photos...

With apologies for being 'not brilliant' but the engine was running at the time.

The little meter is displaying battery voltage (showing low - I have to calibrate it yet which will be done today) and charging current.

The batteries were fully charged when I got to the boat last night - 200w of solar doing their job even in the poor weather we have had.  The only current drawn in darkness has been the fridge and a little for the led lights, pump etc.  The radio draws around 0.6 A and was on until bed time :D

According to the little meter, with only the radio on discarge is shown as hovering around 0.6 A so probably reasonably accurate.

Charging current is only being shown as in the region of 6 A - when deliberately increasing the load (turning the fridge up!) charge current drops by the couple of amps the fridge draws but alternator output as displayed on the panel does not increase.

At the time the photos were taken solar was only providing 400 mA to the batteries so can be discounted (the sun shining brightly in the sky but the panels shaded by the big tree across the canal).

I set the MPPT controller for solar at 13.8v (which was the battery state yesterday) increasing it when the batteries are shown as charged and the panels are generating a reasonable output sees a corresponding increase in battery voltage so I believe the batteries may not be stuffed quite yet.

An A127 recon alternator can be purchased from Flea Bay for not a lot of pennies so replacing it may not be too painful (and if this shows an improvement a good - non Chinese - one could be purchased and the cheap one kept as a 'spare' )

 

Thanks to everyone who has been replying even without any pictures - you are all being very helpful.

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Ps.before you replace the alternator PS. measure the voltage direct at the batteries ,and measure the voltage direct at the alternator , if there is an big difference , its posseble the resistance in the wires is too high , maybe , i have the same thornycroft control panel my alternator is replaced a year ago for a Bosch 55 A from a Ford Orion diesel (20 Euro) by full charging it gave 55 amp , the needle off the Original thornycroft charging meter is in the right corner ....

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7 hours ago, Dutchie said:

I think your alternator is a the original A127 , 35/40 amps in normal use (Max) , max voltage depends off length of wires but never exceed 13,8 volt ,  but a picture says more .

a question : when switching on a few  domestic users : did the amps grow up to maximum ? Voltage drop ?

you wrote the batteries are a few weeks old , did you charge them full before replacing the old batteries ?

 

I think this is not far short of cods wallop.

The "original alternators fitted to BMC 1.5s was the 10 or 11 AC with external regulator etc. I agree this en was  regulated at 13.8 volts.

Then came the ACR series with the big plastic end cover and there were a number of different versions with similar outputs to the 34 to 40 amps quoted above but some went much higher and some were available as battery sensed. (The 10 & 11AC were battery sensed). These typically had regulators set closer to 14.2 volts.

Now we have the A127 range and although they probably started at about 45 to 50 amps output they are now available with a 70 amp output. They tended to have their regulators set for 14.2 but higher voltage regulators have been available for some time so we can not give chapter and verse on exactly what the maximum output and the regulated voltage will be.

The A127 has the same mounting dimensions as the AC and ACR series so A127s are a direct swap except in the case of the AC series you need to remove the external control gear and in all cases ensure the main charging cables are large enough for what will probably be a much higher output.

The OP has an A127 and the output is so low the most likely problem is blown diodes. However it is always a good idea to check all the main charging cables are large enough and terminals tight and clean. 

If its a single alternator engine then a conventional split charge diode system WILL degrade the charging performance unless the alternator is battery sensing or you have a battery sensing advanced controller fitted. In this case my advice is fit a voltage sensitive split charge relay.

 

 

Edited by Tony Brooks
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Thanks to all of you for your suggestions, they are always appreciated.

I have bought a 'remanufactured' A127 75A Alternator (from Ebay) which arrived yesterday as it makes sense to start with the simplest bit to replace. I also have a couple of lengths of 25mm cable to uprate the current wiring as it is both old and not particularly heavy duty.

The connections on the existing alternator were removed, cleaned and re-made while I was on the boat but made no difference to the charging output.

The split charge relay appears to be of the Lucas type that switches from the charge indicator so I don't believe it contains a lossy diode, although I am seriously considering replacing it with a voltage sensing version - as suggested in the last response. (there is a strong likelyhood that the Lucas relay is only in the region of 60A so may prove unsuitable with the new alternator)

As it will be a few days until I return to the boat I won't be in a position to post an update on progress until then so fingers crossed.

All that remains in the immediate electrical fun is to find the wiring to / from the relay that controls the heater plugs as the new (higher current draw) plugs caused a wisp of smoke from the relay and no longer functioning heater plugs - these things are sent to try us!

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Regarding the split charge relay, you could consider moving the alternator positive feed to the domestic batteries, and then the split charge relay connects it to the starter battery which only need a small charge after a normal start. This keeps the current through the relay much, much lower than if the alternator positive goes to the engine battery, and then to the domestics via the relay.

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4 hours ago, Tony Brooks said:

As above. I suspect more relays are killed by people taking the easy option and leaving the alternator output connected to the engine battery than any other cause. This includes VSRs

'Helps' if the relay is made of thermoplastic and has poorly crimped and poorly supported connecting cables pulling on the terminals. :rolleyes:

Edited by smileypete
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Well - yes, its fine for us to talk about that but how many boaters can tell the difference between thermo-plastic and thermo-setting plastic. I havn't seen a relay with a ceramic base for ages, possibly ever. Even paxalon seems to have gone.

The same applies to battery master switches but invisible internal components are involved with those as well.

Edited by Tony Brooks
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I like the tip for connecting the alternator output to the leisure bank, thanks, that makes good sense.

I ordered a sensing split charge relay today so should see it arrive early next week.  So it will be a case of change both devices over and see if anything good happens...

Like Tony, it must be more than 20 years since I saw a relay in ceramic (or Paxolin) as a mount, thermoplastic  - with all its inherent drawbacks - is cheaper to produce and more attractive to those doing fit out. (not only in auto / boats but also in radio transceivers)

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On 07/07/2017 at 19:20, Tony Brooks said:

Well - yes, its fine for us to talk about that but how many boaters can tell the difference between thermo-plastic and thermo-setting plastic. I havn't seen a relay with a ceramic base for ages, possibly ever. Even paxalon seems to have gone.

The same applies to battery master switches but invisible internal components are involved with those as well.

 

I confess to only knowing from recent experiences with 3D printing.

For possible enlightenment:

https://en.wikipedia.org/wiki/Thermoplastic

" becomes pliable or moldable above a specific temperature and solidifies upon cooling"

https://en.wikipedia.org/wiki/Thermosetting_polymer

" a soft solid or viscous liquid state that changes irreversibly into an infusible, insoluble polymer network by curing "

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I think that we just have to accept many electrical items will be made from thermoplastic so its up to use to ensure they are overspecced current wise, the terminals are large enough the adjacent cables are large enough and the terminals are kept tight.

The easiest way to identify thermoplastic is to touch it with a hot soldering iron or something.

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  • 3 weeks later...

Back on the boat again for a few days, so got on with some of the chores already mentioned.

The split charge relay is 120A - not the 60 as previously thought - so I removed it and replaced it with the electronic equivalent.  The relay was just connected with the coil being activated when the alternator is busy doing its thing, no diodes or anything else nasty.  Nice chunky bolt terminals too, perfect!

The aforementioned chunky relay has now been wired into the heater plug circuit (with 6mm cable out) after pulling out the light duty and very fried relay that had also melted the (thermoplastic) base in its enthusiasm to heat up the new super plugs, a couple of happy hours spent there.

It is interesting that the heater circuit uses 2 relays, the first of which only appears to connect the negative feed to the engine block, (as well as providing a negative feed to the second relay) is this common practise?

This preamble brings me around to the replacement alternator - the current is a Lucas Marine A127 (50A) with insulated return - the new one is common return with the case providing the negative connection.  Am I correct in assuming that I shouldn't put this on as a replacement due to no insulated return?  Any advice much appreciated.

So as it stands the original alternator remains in circuit - it would only take me an hour or so to fit the new one (now knowing the way to get it off / on without dropping the spacer into the oily bilge again! ) should anyone advise it could be done without messing things up. (Guess I am thinking of Tony in the first instance, not excluding anyone else who has contributed equally intelligently)

Thanks in advance to all.

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Marine alternators tend to be insulated return. Not too sure why really. Marine as in for use at sea. Narrowboat alternators tend to be common/case return. So no reason not to use it. Just connect the -ve wire to some convenient bolt near the alternator (paint scraped off etc)

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Two relay solution for the glowplugs is not common on BMCs but I think may Listers use a relay to connect the negative for starting etc and then disconnect it making an earth return block insulated return. Personally on an inland negative earth boat  would not worry and do away with this relay making the engine earth return. Just make sure you have a bonding cable between block and hull with the battery negative battery terminating on the block. The starter wiring MIGHT need. a negative connection to the block.

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Job done, the new alternator is fitted and the return cable taken from the case (as indicated in the very helpful sheet included with the alternator) without any problems.

The output reached a brief 40A according to the ammeter on the console  - the highest I'd ever seen on the boat - then settled down to around 20A or so once the initial rush was over with the feed to the domestic bank showing 20+ to 10 Amps over time so good in my opinion :clapping:

My thanks to everyone who contributed their knowledge and advice, the help is much appreciated.

Next little job is to sort out where all of the charging circuit wires go, then I can get the domestic bank first in the alternator output chain, but that is for next week!

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