Friday, 31 October 2014

The Bow Thruster Battery Bank

I failed to mention in yesterday’s post that I almost asphyxiated myself removing everything from the bow thruster locker in an effort to find the source of the smell.  Now I realise what submarine crews have to contend with.  It wouldn’t be a pleasant way to die!

The defective sealed battery was venting quite badly and I needed to get it out of the locker and off the boat.  Raising the cratch cover allowed more fresh air to circulate and by working swiftly I was able to disconnect the terminals.  But not before turning the Bow battery isolation switch off.  Just to make sure there was no shorting of cables I seriously taped the ends of the removed cables.  The battery was then placed on the towpath where it continued to vent and cool.  By this morning it was as dead as a dodo. 

We headed towards Braunston just before 10.00am and moored on the Midland Chandlers customer mooring.  Obviously batteries were high on the shopping list but I also wanted a couple of replacement fenders and a chrome cupboard hook to to replace the one broken on the rear cabin doors.  The swindlers had batteries in stock and before purchasing I made sure they would take the old batteries as part of the purchase.  When one battery fails it’s best to replace all the batteries in that bank as the faulty battery can have affected the others.  Consequently we needed to replace both batteries.  They have a dual terminal setup with both threaded and non thread studs.  Fortunately the swindlers had suitable replacement batteries in stock and they would also take the old batteries.  I assume these get recycled for the lead.  I was rather pleased when the sales assistant told me he would give me a 20% discount as I was buying two.  The rest of the morning was then spent replacing the batteries.

Unfortunately it wasn’t a simple job of taking the old out and replacement them with the new.  The new didn’t have exactly the same terminal layout and I had to modify the timber battery case.  This required the removal of part of a timber lip inside the case and the only saw we own has a very fine tooth 6” flexible blade.  However by taking it slowly I got there in the end.  Once the batteries were secured I turned on the isolation switch and Jan tested the electric pole.  We were back in action.

Everything was re-stowed back in the locker and we moved off to find a vacant mooring just beyond the first entrance to Braunston Marina. Mick and Pip (nb Lillyanne) are in front.  We first met them when going in opposite directions on the Leeds – Liverpool Canal a lifetime ago!  Jan and I thought they were around Birmingham and got a surprise to see them in Braunston.  Mick is still attempting to resolve their problem of insufficient heat getting to the calorifier.

In the afternoon I wandered around to Tradeline Rope & Fenders to purchase another two of their excellent rope shackles.  We used one to secure the centrelines to the roof and appear to have misplaced our spare.  At £4.50 each I find them good value for money and it saves the paintwork on the roof.

Next stop was the chandlers at Bottom Lock where I managed to purchase a replacement chrome cupboard hook for the rear cabin doors.  At £11 it wasn’t cheap but we need it otherwise it’s very difficult to secure the doors in the closed position when we’re both on the stern.

Last job for the day was to have another play do some serious investigating into the TV signal reception. Braunston probably isn’t the best location to do this as I’ve noticed the surrounding houses have aerials pointing at 180deg to each other.  If I can’t solve the conundrum here then we’ll have another look at it when moored in a more exposed location.


Brian and Diana on NB Harnser said...

It may be worthwhile checking the charge voltage is not to high if you are using a mains or A to B charger for the BT batteries.

Tom and Jan said...

Hi Brian

Yes I have thought that might be a possible cause. However I would need to makesome significant changes to the system to achieve that. The PDAR is raising the voltage to 14.8 for the Rolls batteries to be effectively managed and the Smartbank combines the output. The BT batteries are connected in parallel with the starter battery.

Don McCoskrie said...

I suspect that the thruster battery is being overcharged if connected across a wet battery.
As you seldom use the thruster(due to you superior boat handling skills) a small amount of charge will be required for the thruster battery. Why not setup a mains powered sla charger that would be run only when the engine is running? The other way would be to use a constant voltage (13.8v) charger circuit fed from your wet battery. A suitable circuit was in Silicon Chip magazine 07/92.

Tom and Jan said...

Hi Don,

Actually I suspect the problem might be over voltage related because I have been using the BT too much. The BT batteries are connected in parallel to the started battery. These are charged from the smaller alternator (65A) and when the sensor on the starter battery identifies it (the starter battery) has been recharged it disconnected the 65A alternator and combines it with the 175A alternator that charges the domestic bank at 14.8V.
If I've used the BT too much then the BT batteries may not be full charged by the time the starter battery is and the BT batteries then receive 14.8V. I don't want to change the charging system so I'll now use the BT less and accept I might have to replace the two batteries every 2-3 years

Don McCoskrie said...

I've had another thought... If you inserted a high current rectifier diode in the charge lead to the bow thruster battery the voltage drop across the diode would be 0.8v resulting in a maximum charge voltage to the BT battery of a much more tolerable 14.0v. An example of a suitable device would be: This would be an easy fix that would much cheaper than replacing the battery. Also what would be the risk if the battery had failed when you were away from the boat?