Wednesday, 30 July 2008

Charging problems part 2

After a while it became clear that the charging fault persisted (see previous post). Perhaps it was a bad earth connection? When the engine is running there are volts across the relay coil, but there's about 2.7V across the switched terminals - about the same as the voltage difference between the starter battery and the leisure batteries. So either the coil voltage isn't enough to energise the relay, or the contacts are high resistance, or there's something else going on which I hadn't spotted. (There was.)

We carried on with the cruise, jumping across both sets of batteries when the engine was running. I occasionally applied my mind to the problem, but didn't get anywhere with it until five days later. Why, I asked myself, was the alternator and other nearby bits of the engine, covered in a black, rubbery powder? The engine was still virtually brand new and should still be bright shiny yellow. The alternator belt. Yes, of course. The alternator belt was loose: perhaps that would explain all. Flat leisure batteries would be loading the alternator enough for the belt to slip and start disintegrating. Must be that. I tightened the belt by moving the alternator almost to the extent of its travel - the belt had been very loose - and checked the charging. As before - still not charging the leisure batteries. Grrrr. Well, now I would have to buy a new belt, and perhaps I could ask at the same time for some advice.

We've jumped forward to Saturday 12th July and we were at Rufford (I'll fill in the missing days later). Walked up to the marina and asked Chris (is that his name?) [edit: no - it's Mark, at St. Mary's Marina] if he carried such items. He didn't, but promised to get his supplier to phone me. Well, perhaps my phone didn't have a signal at the right time ... but he didn't phone.

Thorn Marine

Jumping forward again - I'm doing this in order to keep with this topic, you understand - and now it's Wednesday 16th July 2008 and we're at Stockton Heath and Thorn Marine. At last - a decent chandler's. First thing was to replace the alternator belt as I was worried about the worn one breaking. Ah. No belt the right size. But ... Nigel would order one. Two, actually, as I wanted a spare. It would be there by 0900 the next day, so we went to the London Bridge pub for tea.

Willow sheltering from the rain

The next morning we returned to Thorn Marine (we'd moored a hundred yards up the cut) for the alternator belts. Good. It was there. Yes, "it" - only one had turned up. But no problem: Nigel would order another one straightaway. First I would fit the replacement belt to make sure it was OK - and it was. A bit tight, but once on it was fine. Once the trip boats had been sent out Nigel had a poke around with his multimeter. His verdict: the split charge relay. I wasn't so sure: the replacement relay I'd got from Bridgewater Marina hadn't made any difference - and I'd checked the operation of the original relay "on the bench". Did more measurements ... and ... YES! FAULT FOUND!! It was... can you guess?

I think I'll keep you waiting for the answer and post a "part 3". Well, I had to wait almost two weeks to find out!

While we're in the engine hole, perhaps someone could explain the black rubber pipe which connects the weed hatch to the prop shaft? You can see it has a tap at the weed hatch end. There was no stern tube greaser on this setup. Any ideas?

[edited to correct marina manager's name. Also thanks to Brian for the info on a "greaseless" stern bearing]


Anonymous said...

The black pipe from the weed hatch is a water supply to the stern gland seal, often known as a deep sea seal, as you say no greaser. There has been some discussion on this type of seal on narrowboats as they were origionaly intended for sea going boats, not ones runing in a mud slurry half the time.
for a similar one and Tony Brooks comments

Halfie said...

Yes, that's very interesting, Brian. Thanks for the link. As it's not our boat I wasn't too concerned ... it seemed to do the job, and the bilge was bone dry all the time.