Posted by: suliere | February 12, 2013

The Penny Slowly Drops

Our lithium batteries are simply wonderful and have no problem in putting out 300 amps should we need it. They mean that under sail we can turn on microwaves- even air cons and simply rapidly make up the charge with engines or the gene run for a short time. They always maintain a high voltage even when down to 20% charge, they weight less, last longer and take up less space.

However, recently we have had some issues with the mastervolt charging system. I have two 100 amp chargers – they are inverter/chargers. They start off with up to 200 amps going in but gradually decline – even as low as 65 amps. Tonight I measured the temperature of those chargers and they were 50C!!!! The isolation transformer was 55 c and it was this that was heating them.

I opened the cupboard they were in and switched on the aircons to bring the temperature down and as this happened the charge level increased in accordance with the charging voltage in the manual- so it is purely the charger temperature that is doing the dropping. It seems at 50C we get 65 amps left with some 26 amps going to supply DC things = say 91 amps. At 30 C we get 130 amps plus the 26 background dc items = 156 amps.  The only time we get the 200 amps is when the temperature is 10C….. which is never really the places where we sail.

The issue now is to how to keep the chargers cool and that means down to about ambient temperature which is say 26 to 34C. I guess  this means a combination of insulation from the transformer as well as more ventilation ….. I shall try and solve this very quickly. Of course charging with the 230 amps of alternators. on each engine would be much faster at these higher temperatures. The alternators have been changed to output a 14.2 volt constant voltage.


  1. Breakthrough 🙂 Great news!

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