Battery time - more about them than you ever wanted to know

Our domestic battery bank was getting towards the end of its useful life. The capacity had dropped a bit and we knew that we would have to probably replace them next year. However, as we planned to visit Guernsey for fuel, a south coast haul out seemed sensible. So, we opted to go to Swanwick where we could torture poor Paul from Maricom. They've done most of the more complicated electrical / electronics work on the boat and were accepted by our insurers as OK to do a Lithium battery upgrade for us. That was a glib statement - the insurers (Navigators and General via Towergate) really do not understand much about batteries. One condition they decided to impose was that we "do not charge the batteries off the boat". Er? They are heavy things fitted into lockers to run the domestic system?? So often we found ourselves trying to educated them a bit on battery technology. Almost the blind leading the blind really.

Why lithium now? Well, when we last replaced the 6 domestic batteries, we felt that it was way too immature a technology and the management systems were still pretty primitive with the risks of  batteries simply shutting off etc etc. Things have progressed a lot since. After much head scratching and many hours of research, we decided to go ahead and put in 6 Roamer 24v lithium batteries to replace the 6 12v AGMs. The AGMs were arranged in three 24v banks, giving a realistically useable 390 Amp hours of 24 volt power. You could take out more but at the risk of reducing the expected life of the AGM batteries significantly.

The lithium option gives us a useable 690 Amp hours if we pamper the new batteries and only drop them to around 50%  but you could take out 1100 happily.. A dramatic upgrade! The other big win is that they don't need to be brought to 100% charge regularly. The AGMs like that and if we are using the genset, it takes ages and ends up needing to running the genset on very light loads to finish the charge - which is bad for the genset.  Ironically the lithium batteries are cheaper than a new set of Lifeline AGMs too. Well, the base batteries are but of course you need lots of other modifications to the charging and management system hence lots of boxes of goodies:

We opted not to go to Lithium for the thrusters and anchor winch. Why? Well the powerful motors in those expect to run on AGM batteries where the voltage supplied drops quite a lot under heavy loads. Lithium batteries don't do that in the same way and so the motors would get a higher voltage than they are designed for, not good for their longevity. Hence we simply renewed the AGM banks running those and fitted battery to battery chargers - they will be charged from the massive domestic battery bank in future. (For the real trainspotters, we could have fitted proportional control to the existing thrusters but the cost was £££££. An even nicer solution would be to install new thrusters that are lithium ready but that is £££££££££).

One of the first jobs was to bin the horrible old charging relay setup, which linked the thruster banks to the main battery bank for charging and disconnected them when in use. We were very happy to see the relays and switches involved get ripped out:

The new battery to battery chargers were put in, which will permit proper three stage charging at up to 50 amps. Again, for the terminally bored, AGM batteries like to be charged in three stages and like high charge currents. Using the old "link to the domestic battery bank" approach, they rarely got this. The charge voltages were effectively controlled by what the domestic bank wanted, no matter how depleted the thruster batteries were. It was rare for them to see a bulk charge voltage. The original charging setup was not good for the life of the thruster batteries.

Whilst Paul and his man Mark were struggling to un-plumb the old domestic batteries, we had a walk. There are plenty of "different" craft in Swanwick now and a lot of style over substance it seems. This anchoring arrangement struck us as wildly complex and something that is just guaranteed to jam up sometime. All done so that the anchor is not visible when retracted:

The phrase "it will all end in tears" springs to mind, however anyone buying that boat is most unlikely to do any anchoring in the UK - a blast from Marina restaurant to marina restaurant with the sound system cranked up seems more realistic. 

We used the dinghy crane to lift the old batteries out and into trollies as they weigh around 70Kg each. The cardboard boxes in the foreground contain the new lithium chaps, in the background are the old AGMs and, in the middle, boxed up new AGM batteries for the thrusters:

The old guys looked a bit forlorn, knowing that they were heading to be recycled:

Mind you, they hadn't seen any of the nice places we had visited as they lived in closed compartments in the lazarette so their life was not that exciting anyway.

This is what a new one looks like, emerging from its' wrapping:

They are real lightweights in comparison too - 38Kg each. The weight saving in batteries alone more than compensates for the heavier Brompton bikes we swapped to a while ago! Work was going well, Paul looked happy(ish)

as the inverter / chargers went topless to be reprogrammed for Lithium charging:

with the batteries snug in their new homes:

Switching the boat over to running on those felt like a real step forward. The monitoring kit was duly installed (a Victron Cerbo GX for anyone who is remotely interested) and the screen started to reveal the secrets of the inverter pair and the new batteries:

The alternator needed a special external regulator, we had opted for one called Zeus. Not because it sounds stronger and sexier than a Balmar or a  Wakespeed - we are not that shallow. This was because it had good feedback for the simple app based setup and management, firmware updates, was the preferred solution of the battery suppliers and seemed to fit the bill nicely. It was fitted in a void under the master cabin, just forward of the engine room:

Yes, it is fixed on it's side - so we can see the lights on it easily. The cabling got tidied up after this picture by the way. The alternator itself gets modified to bypass the original internal regulator.

The Zeus box was fitted after we were lifted out of the water and so could not be checked before relaunch (the boatyards dont want you running the main engine whilst you are propped up out of the water. Any induced movement might disturb the props they use to hold the boat upright and that could end badly). We had to wait for life afloat again to test and fully setup the alternator controls. 

Meanwhile, some neat little battery to battery chargers had been fitted to keep the two thruster banks of AGMs topped up and the start banks for the main and wing/genset too. These look after the start batteries:

and these way more powerful chaps (50 amps output at 24 volts, not a weedy 17A) handle the thruster banks:

Things were as complete as they could be, just wating for relaunch to test the alternator charging setup and fine tune things. Good progress. We ran the boat "off grid" whilst out of the water for 4 days and used around 35% of the battery capacity. That included running a coffee machine and an electric kettle via the inverters to keep ourselves and the other workers suitably lubricated. Very happy with that! The proof of the pudding as they say, is to come......