Living With Our Rapido 963f Le Randonneur Motor Home.

Thursday, 15 September 2011

This is sods law at its best.

Isn't is strange, when sods law cuts in, it usually hits with a vengeance? When we had the Webasto heating fitted at the end of June, I also decided to replace our (small) domestic battery bank, as they were original to the boat build, and now approaching six years old. I checked the condition of them just prior to taking the boat in, and one was absolutely fine, but the other was not, although the related equipment, such as our Sterling 1800watt inverter was working as it should, as was the charging system through the Sterling Pro Digital Alternator Regulator. As soon as I picked the boat up, after the work, I noticed that the charge lamp on the volt-meter for the domestic side, was flickering on tick-over, and the associated warning buzzer was chirping. This would cease as engine revs increased, and would stop altogether when the engine had run a while. As we were not going to be using the boat after this, until Tom and Jan, who write their blog Waiouru, were to take her over for a while towards the end of the year, I didn't investigate any further.

It was at the end of August when Tom came aboard, and he found that the inverter was also not working, but alarming, showing it was not receiving sufficient 12V supply. This was strange, as during the process of checking the batteries earlier, I had also tested the inverter, and it worked perfectly. Our small domestic batteries were sufficient for out needs, and would last one overnight stay, without any further charging, so I expected the new batteries to be slightly better. We also have C-Tek multi-stage chargers, of the correct size for our batteries, which are connected directly via fuses, and were showing the batteries fully charged. Nantwich Marina, (formerly known as Nantwich Canal Centre), who completed the job of installing the Webasto and the new batteries were contacted, and they kindly arranged an "after-sales visit" to the boat by a technician, in order to diagnose the cause of the problem. This is what he found:

This is a photograph of the Sterling PDAR in operation, engine running, and both "fault" conditions still present. This shows it to be working exactly as it should, the top green LED on, showing boost charge. The second, yellow LED, not yet on, as the countdown timer to float charge mode has not yet activated. The third green LED not on, as float charge mode had not yet been reached. The middle yellow LED indicates that the PDAR is set up for lead acid batteries, and the bottom yellow one shows it is set for a 12V system. The top green light also flashes for several minutes on start-up, signifying a "soft start" charging process, which prevents alternator belt slip. The charge voltage to the batteries rises gradually, until full boost level is reached.

The NCC technician measured excessive voltage from the alternator, but the PDAR has an excessive voltage safety cut-out, with an alarm mode, which is all lights flashing together. As this shows correct operation, I believe we can discount that for the time being.

These are the C-Tek multi stage chargers. The top one charges the engine start battery, the bottom one charges the domestic bank. They both have programmes which test the condition of the batteries before proceeding to charge mode. As the batteries become fully charged, they both show a green light at the top of the "ladder", indicating they have reverted to float mode Then periodic testing takes place, and the automatic charge cycle starts again. They are connected directly to the batteries via fuses, and both show fully charged batteries eventually.

Now, this appears to be the cause of the problem - a simple battery isolation switch. The boat is fitted with two, one for the domestic side, and one for the engine start side. When the new batteries were fitted, the switch was obviously turned off for safety reasons. It was returned to its on position at the completion of the job. The NCC technician found that if he "jiggled" this switch, the inverter would start to work, with no alarm, and if "jiggled" again, it would stop again. It would appear, as all the low current consumption interior lighting was working, but the inverter wasn't, that the switch had become very high resistance, either due to corroded contacts, or weak springs within it, or a combination of both. This picture is of a new replacement, exactly the same design as the old one, so hopefully the job should be easy. Or is that an invitation for Sod to do his worst again? My thanks go once again to Nantwich Marina, for their follow up call, for which there was no charge. Hopefully, the switch will rectify both the problems totally. If the charge light fault remains, then sods law will have cut in again, and no doubt we will require a new alternator, when there was previously nothing wrong with it!

*The Sterling PDAR, Sterling Power Products, converts the engine's standard alternator into a 4 stage smart battery charger, and gives not only a quick recharge under controlled conditions with built in safety features, but also allows the batteries to accept a far greater level of charge than with just a standard alternator. The downside is, that the battery fluid levels have to be monitored more regularly, as faster charging always equals greater fluid loss.


  1. We will find out on Saturday if the theory is correct!

  2. I am again confident that my long thought out theory from afar is correct! This time it has the backing of someone who has gone through a hands on fault finding process to actually identify a faulty part. With a correct output voltage at the alternator, and a wildly fluctuating one at the battery switch, also tells me the high resistance nature of the faulty switch could also be at the bottom of the apparent charging problem. We will see.

  3. Solution. We visited Tom and Jan at the boat on Saturday, armed with our new, but inexpensive replacement isolation switch. This was replaced, but the fault remained. The original switch was then cleaned and replaced, and a logical fault finding process was put into place, with the assistance of Tom, who turned the inverter on and off as requested, while I tested the circuit backwards. Voilà, a tight, but corroded, bolted connection was found to be arcing every time the inverter was switched on. The joint was undone, cleaned, coated with petroleum jelly, and rebuilt. This problem was found in the area of the wiring loom where the wiring for the new Webasto had been added. The result is that the inverter now works as it should, and the problem with the charging light and warning buzzer at tick-over has disappeared. Job done, no alternator, or switch required. The moral of the story here is - take nothing for granted, and even though the symptoms may look complicated, look for the simple solution first. I also rectified a loose earth connection to the engine start battery while I was there.


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