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Iskra Travelpower alternator freewheel


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Our Travelpower has started playing up after 7 years / 2600 hrs faultless operation. Symptoms are that under a heavish load (2kw) there is an intermittent noise and the (silver box, with remote panel) TP drops into standby reporting low rpm for a few seconds, then recovers. Hard to describe the exact noise. Not totally dissimilar to an arc, or a mechanical whir or grating. Having taken the alternator off and checked the brushes / slip rings, which are fine, I have a theory that it could be the freewheeling pulley slipping. This has always been a bit noisy on over-run (ie when the TP is off, the engine is slowed rapidly (going from a reverse thrash to neutral for example) you can hear the freewheel grating a bit as the alternator spins down slowly.

So, anyone with any experience of this problem? Does my diagnosis sound likely? Any short term fix, e.g. a bit of 3in 1 onto the sprag clutch rollers, or will that make it worse? Ultimately I'll get a new pulley but we are in Bristol at the moment, 3 weeks from home and I'd like a short term bodge to get us home (well, get us home whilst being able to use the washing machine, tumble drier and electric kettle!).

 

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Edited by nicknorman
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I can't see how a bit of 3 in 1 would hurt.  They are usually either oil or grease lunricated so maybe it's dried out (or maybe the clutch is simply worn of course). If it makes it a bit worse are you really much worse off?

Edited by WotEver
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37 minutes ago, Sir Nibble said:

Don't think it will help, horrible things. You are going to need a special tool to change it too.

perhaps if I can identify it from the picture I could have one sent to you and you could get it fitted.

Thanks Snibs, if you have any bright ideas for replacing it I'd like to hear them! Trouble is, I live in Aberdeen and the boat lives at Fazeley so any repair is going to have to be done on the boat, as opposed to in my garage at home (we fly to and from the boat). I think the best option might be to take it to Cox's which is just a few miles away at Atherstone. They do seem to be pretty expensive though!

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  • 2 weeks later...

No. If anything, it made it worse. It also occurred to me that the thing slipping was one thing, but when it gripped again there could be a very large torque on the alternator spindle which probably wasn't very good for it. But at least I'm certain of the problem. I've been in touch with Ed Shiers who has an alternative make of freewheeling pulley and I'll get him to post it to me so it arrives at the marina when we get back in a week or so. In the meantime, I'm realising how good it is to have a Travelpower - by how much we miss it! I think if it wasn't quite so hot, I wouldn't mind generating 2kw from the 175A 12v alternator for eg the tumble drier, but I'm worried about overheating our only source of generated power by running it thathard for an hour or so. Our engine bay isn't particularly well ventilated.

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  • 2 weeks later...

Update. Ed shipped the pulley so it was at the marina when we got back yesterday, along with a tool for holding the pulley for undoing. "Great!", I thought! In fact contrary to what I said earlier, the pulley is not on a spline, the spines part of the pulley is purely to take holding tool. In the centre of the alternator shaft is an 8mm hex socket. So I presumed this was a bolt and the way to go was to hold the pulley stationary with the splined too, and unscrew the bolt. Hmmm well after much bending of spanners and hammer-battering last night, that wasn't working! Grrrr!

Ed mentioned that he would be nearby today so I texted him yesterday evening and he said he could come to the marina at 10:45 this morning, which he duly did, armed with an impact wrench. The pulley was thus impacted off in seconds and I could see that there was no bolt, the pulley simply screwed onto a thread on the alternator shaft. Apart from the fact that I had been shocking the wrong bit (alternator spindle instead of pulley), I'm fairly sure I was trying to turn it the wrong way. Doh!

The new pulley, although a perfect fit on the shaft, is a slightly different length - but Ed had sent me some shims which we packed between pulley and alternator so as to position the belt bit in exactly the same place. Ed left at that point, having asked for a pittance for his time (I gave him double, which was still cheap).

I walked to Toolstation to get a steel rule to check alignment of the pulleys. This can be adjusted by loosening the bolt holding the alternator bracket. I've stopped for lunch but I can see that there is a slight angular misalignment which will be worth correcting to maximise belt life - obviously it's always been like that. In terms of fore/aft alignment, Ed's shims have made it pretty much perfect.

So I learnt about Iskra alternator pulleys today. Like so much stuff, easy to misunderstand how it goes together when it's together, bleedin' obvious when it's apart!

And absolutely full marks for Ed Shiers, a very knowledgable, competent, helpful, pleasant, reliable and reasonably-priced chap. You don't find many of them!

  • Happy 1
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With everything bolted up, I checked the angular alignment again and in fact it is perfect (apparent slight error was due to there being more "land" between the edge of the belt and the front of the pulley on the alternator pulley vs the crankshaft pulley). Ditto the fore/aft alignment.

Only slight problem is originally, the bolt through the slot on the adjusting arm was very near the end of the long slot. The new pulley is slightly smaller diameter (by a mm or two) and I am just hitting the end of the slot with the correct belt tension, so no further scope for tensioning, but then the belt has done 1000hrs and only been adjusted once so it's probably not an issue or if it is, there is scope to elongate the slot a bit.

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8 minutes ago, Old Son said:

But does it all work????

Yes, elongated the slot a bit (but it's aluminium and I don't really have the right tools for it). Retensioned main alternator belt and TP belt, fired it up and all is fine.

Actually one interesting thing I've noticed during testing is thus:

Using the 2kw tumble drier as a steady load:

Set engine rpm to 1100 in neutral. Turn on TP, turn on tumble drier. Engine revs decreases to 1050.

Switch off TP so that the inverter takes the load, fed by the 175A alternator (which is just about capable of feeding the inverter with enough current so the inverter can produce 2kw without taking any current from the batteries) and the engine revs drops to 1000rpm. So it seems that the TP is a lot more efficient than using the 12v alternator/inverter.

I'd noticed before that the engine seemed to labour more with say the electric kettle run from the alternator rather than the TP, but hadn't quantified it to see just how much more. It's a lot more!

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1 hour ago, Sir Nibble said:

The faster you spin an alternator, the less torque it absorbes for a given output. I suspect it is less generator efficiency and more the 14Vdc to 230V ac conversion that explains the difference.

Your first sentence is correct but not relevant. Assuming 100% efficiency, for an alternator to produce a certain amount of power the torque is inversely proportional to the rpm as you say. However from the engine's point of view, a certain torque for a given engine rpm is required to deliver the power to the alternator. So the pulley ratios and hence alternator speeds are irrelevant, provided the alternator speed is adequate for the desired output power. In any case, the pulley ratios on our alternator and TP are very similar.

The inverter efficiency is quoted as >90%. I don't know what the TP magic box efficiency is but it is probably similar. Where the difference is I suspect in the transfer of power at 12v vs high voltage.

We have about 1m of 70mm^2 cabling (x2 round trip) between inverter and batteries. Ditto between alternator and batteries. Obviously some power is lost here but not massively so.

My conclusion is therefore that the difference lies in the efficiency of the 12v vs TP alternators. Whilst the former has 160A or so going through its stator, is working pretty much flat out, and is considerably bigger physically than the TP, the TP, working at 300v or so, has about 1/20th of the current and is only working at ~half power despite being physically quite a bit smaller.

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