I have a 60ft narrowboat which I am just about to move onto permanently.
I currently have 5 batteries a 110Ah heavy duty starter battery (new) and 4 x 110Ah leisure batteries connected together for the domestic power. I also have a Victron inverter/charger for the 240v side and a Honda 2300w petrol gennie as back up. The engine has 2 alternators one for the starter battery and one (I think 35amp) for the domestic battery bank. On the load side I have the normal lights and water pumps, a microwave, an electric kettle and a washing machine.!My questions are, could I reduce the domestics to 90Ah units ? & could I mix 2 x110Ah and 2 x 90Ah units together ? Is it worth getting a battery management unit in addition to the Victron ?
The main reason is that I think the existing batteries have been discharged a few times below the “safe” level and are tired and secondly I have the chance to buy some Bosch batteries at a discount price but only for a couple more weeks. I would buy 4 the 110Ah units but cannot get the terminal configuration to fit my battery box whereas the 90Ah units ate available “left” or “right” handed.
1. I hope you’re wrong about the domestic alternator only being a 35 amp unit. This would be fine for an engine battery, but not for your domestic ones.
2. The Victron is no help whilst away from a shore line.
First you must do a power audit – details of how on www.tb-training.co.uk in course notes. This will require you to calculate the amperage drawn by all your electrical equipment and an estimate of how long you use it for per day.
Divide battery powered equipment wattages by 12 and inverter powered equipment wattages by 10. Multiply inverter powered equipment amperes (if given) by 20 to get amps for the power audit.
If 30% of your battery capacity is less figure found in the power audit either fit an advanced alternator controller and recalculate using 48% or install higher capacity batteries.
You then need to decide upon a “nearly worst case” time you will run your engine for in a day – the “day could be two days if you tie up for a couple of days in each town.
Then (and this is only a rough guide) multiply half the alternators rated output by the time you get in the above paragraph. If this gives a figure in amp hours that is less than that given in the power audit, you need a larger alternator.
If the charging current after about 10 mins running is more than about 20% of the capacity of the battery bank, fit more batteries. This will maximise battery life. 5 X 110 ah batteries allow about 100 amp input, and as this would probably cause problems for an ordinary V belt, this will probably not be an issue.
Only after you have done all this can you get an answer to your questions.
It is probably not good practice to mix battery capacities, but may well work – it all depends how much cheaper they are – and do Bosch supply deep cycle batteries? Please do not use engine batteries for the domestics unless they are so cheap you can throw them after a couple of years if you need to.
If you change from 110ah to 90ah you will be loosing 80ah capacity, which is nearly another battery. As the batteries will only deliver about 30% of their rated capacity and you have a lot of high current devices I could not advise changing to 90 ah.
90 Ah will be fine for the engine.
I would always advocate an advanced alternator controller because :
1. It will charge your batteries to about 98% fully charged as opposed to 80% with a standard regulator.
2. It will convert your (probably) machine sensed alternator to battery sensed (if you do not understand some electrical notes should be on the above website by the end of April).
3. The higher state of charge will minimise sulphation, although this is less of a problem for liveaboards where the batteries are always charging or discharging.
My notes name the make that I feel makes the optimum product.
Sorry about the technical stuff and maths, but if you do not do it, how can you know what you dealing with?
