Energy Storage #4

I have been lazy, this blog is written in January 2021 whilst most of the work was carried out during 5 weeks in July 2020. What happened? Finally we had a window of opportunity to fly from Sweden to Artemis in south Italy. We went from summer to blazing hot mediterrenaan heat. Inside Artemis the temperatures was always around 36 degrees C. Such temps slow you down a bit. But the job got done. This is what happened.

As you can se it wasl quite dry. The high outside temp was due to the temp sensor was exposed to the sun. 

This was the pallet box we used to freight "stuff" from Stockholm to Italy a couple of times. It´s last voyage contained the two battery packs. Due to Corona it arrived already four months before and was stored safely indoors by the marina. For which I am very grateful. 

A few days after we arrived we managed to access the container and not without some effort my first mate and I managed to move the two packs onboard. They weigh in at 58 kgs each. I hade some concern that the sharp edges of the packs would damage wood and gelcoat if we did mishandle it due to the weight. The last move, down the steps into the salon I needed help with and the the boat was not yet ready to accept them. Some things had to be done first.

With the floor boards off, it becomes obvious of the challenge at hand. The batteries directly below the stairs are for the engine start. Two 12V 200Ah in parallell. Having checked them out they where in good condition. It was rewired so that the engine just uses one of them, this is still an overkill as it is exclusively used for the engine power circuit, nothing else. The other battery is now used for the ships 12 volt service. Very few things run of this voltage, basically only navigation instruments, radios and smaller 12volt electronics. The plan is relocate and replace this with a dedicated LFP bank using a better charging scheme. Bit for now this had to work. 

The two batteries to the left where used to ensure the boat had power during the rebuild, bit like a heart&lung machine in open chest surgery. For sure was Artemis chest exposed. This space, from the first battery by the steps up forward to the mastfoot is the length of the keel. Meaning that below these batteries is the bilge. Hence, the current arrangement basically hid the bilge, except fo the foremost part. 

The next task as seen in the picture was to get the two batteries in the middle out. If you look more closely the challenge can be seen. You can´t move the cells forward as they will be stopped by the battery plus and minus posts. The other way, backwards and up was not possible due to the wooden floor beam blocking the upward movement. 

Closeup above shows this. Neither was there room to twist the batteries sideways it seemed. All attempts aggravated by the heavy cells and that I was sliding around on the floor due to my own profuse sweating in the 36degree temperature. 

Eventually I figured it out. The first of the two batteries, the rightmost one could be twisted just enough if cables and hose where removed. When this battery was out the left one came out by the same means. 

Now, the hidden bilge was exposed and look what we found, another bilge pump, disconnected. Bet this happened when Artemis was in the US and got the West Marine batteries installed.  

We now had two bilge spaces cleared out and the original plan was to house the LFP packs in each of them. The aftmost space would take pack #1 but the space with the hidden bilge pump was not ideal, I did not like the idea of covering the bilge like this and I most definitely had plans to have belts and braces in my emergency bilge strategy and this space was needed for it. Time to be think, was there another space that could take pack #2?

Artemis hull looks like a big dingy, almost flat bottom with a long narrow keel. Bruce Farr wanted her to sail well and sure she does. The result is that the usual ample space beneath floorboards on more traditional hulls is not all that present. But, as luck has it. There was a space left beneath the dining table seat. With tape measure in hand the LFP pack #2 just had room. But the hole was no large enough. With aid of the sabre saw, the whole was increased. As it turns out, when Beneteau assembles their interiors the use screws and no glue. I have had reason to be grateful for this on more than one occasion. 

Now with pack #2 located next was to deal with the exposed space where I wanted to have access to the bilge for pumps. The picture shows a pump placed as wanted, a separate post will explain the strategy here. What you can see are four shiny aluminium L-brackets. These where epoxied and screwed in place and are there to hold two of the lead acid batteries taken out. Why?

This installation is only a part in a longer electrical refit project. I needed to have the 10kWh LFP bank in service soonest, as the lead acid cells used for the 24 service bank had lost capacity. For days sail it worked if you charged overnight. 24 volts are used for windlass, winches and bowthruster plus sail furling. It has to work. Sure, one could fire up the 9kw Onan and charge as backup but this is not very practical and it simply moves the issue forward. Electrically LFP banks must protect themselves by being under control of  BMS. This unit has two tasks. The first is to balance the cells in the pack, the other is to protect the cells form under or overvoltage. The BMS does this by simply disconnecting the pack for charger and from load depending on what happens first. So, whilst the batteries are protected what happens with the rest of the circuit, the charging and the loads? As for charging, in particular with engine running and the generator on it charging the cells, a sudden disconnect of the LFP will happen. This is called load-dumping and can damage the generator as well as produce voltage spikes that damage some of the loads. The only correct way to solve this is to have a system whereby you separate the charging and load to a from the LFP battery pack. This is not implemented on Artemis but will be. It will be in a separate post too. In the meantime a lead-acid battery pack acts as a load to the charging and it also ensures the LFP does not create a system blackout if the BMS decides to protect the the LFP´s. Hence, this is what is located on the L-brackets. Two 12volt 100Ah lead-acid batteries.

As seen to the left with said lead-acid located, the bilge can still be accessed where the auxiliary high capacity pump is located. 

Two more L-brackets have been screwed and epoxied in place to be ready to receive LFP pack #1. Whilst having the floor exposed some effort was made to bring some order to the chaos that boats suffer when new wires and hoses are added. Typically bothersome are sloppy jobs where the installer can´t be bothered to do clean routing. It is almost impossible to do a satisfactory job of this afterwards, but we tried. 

Below you can see LFP pack #1located. Still the protective pink film overt the acrylic cover remains but the pack is in service. Mostly it went smoothly. A risk I took initially and which I got lucky on was that I had taken measures of the part of the bilge that was accessible without taking all those cells out. Had this been my only option I would have had to remove the floor beams, a major job. Another miss of mine was not to think how it would be to connect the thick high current cables to the relays (a.k.a contactors). As the packs arrived the relays where mounted right way up. But laying on ones stomach trying to get several cables onto same bolt while putting on a washer (yes sweating profusely) and nut knowing well that if I dropped it it would be gone into the bilge. Then getting a socket wrench onto this would not have worked. So I rearranged the relays so they faced upwards. As annoying as it was to cut up nicely routed signal cables (some too short now) it turned out well. 

What I did not relocate was the manual relay disconnect. It is a simple but very useful function that allows to separately turn off the charge and discharge relays. Everytime Artemis is left alone, the switches ensures that if anything else fails, the LFP batteries will never be over or undercharged. Leaving LFP´s for longer periods without charging is fine, they should never be tricklecharged. 

Relay switches in this grey box mounted on pack #1

Relay in the original correct upright position that turned out to be very awkward. Below shows them relocated. 

The grey, blue and black cables routed along the bulkhead go to the other LFP pack, #2. 2x35 sq.mm cable is used. It may appear low but keep in mind this is 24 volts why it effectively is 140sq.mm. After having fought with thicker single cables in Artemis original electrics I decided to never go above 35sq.mm cable area as this is the limit of being able to nicely navigate around bends and corners. Just use additional 35mm´s instead. The grey cable is the communication for the balancing PCB´s on the packs.

Originally the lead acid cells had several cables attached to the battery posts, this was deemed too much for the relay post to hold. This was solved with two L-brackets screwed to the bulkhead and serving has high-current distribution posts.

How did it work? This will follow in the next post on the powering of Artemis.