Hi,
Per subject. Part of my build process was to convert for the same price and system weight or less than a replacement 10 or 12hp diesel.
With hindsight the following has occurred to me. Please bear in mind my sailing boat, as it is a double ender is restricted for motor form factor and battery size/s, system components etc that could be fitted into the available engine space volume. She's 26ft LOA.
My base system before upgrades is a nominal 24V/110 amp continuous direct drive system.
I became aware that it was cheaper and from an engineering point of view better to use the largest physical size batteries as the resistance and cost per amp hour was less if using say 2 x 260 AH AGMs 8 D size rather than say 4 x 130 AGMs in series.
Obviously the difference too is one gives a nominal system voltage of 24V and the other 48V BUT as my controller sees whatever voltage you throw at it between 24 and 48V, it begs the question which choice would be more economic in the long run?
It is easy then if you want a nominal 24V/110A=2.5kw system that it might be best to use 4 x 130AHs at 48V and limit max throttle in the controller by percentage of the nominal system voltage. In effect if I'd used 48V I could when considering voltage drop due to system losses and drop due to SOC/DOD have set up the system to equate to say 30V input, bearing in mind a nominal 24V system when the batteries discharge may drop to 21V, and less by the time the voltage arrives at the motor.
Either way I would still be using the same wattage for any given speed regardless of nominal system voltage. If using 2:1 gearing (which there is really not enough space for) I'd halve the current with twice the voltage for same power output as the 24V direct drive but I'd then need more costly and larger 48V chargers, say 600 Watts 24V compared to a 1200 Watts for a 48V charger plus more batteries.
Another way could be to use 2 separate 24V packs and switch over so you have a fresh higher voltage pack in reserve rather than say a depleted 24V pack. Then would 2 x 24V 600 Watt chargers cost more than one 1200 Watt 48V charger.
All food for though and as I could not afford Lifeline batteries which specify Reserve Capacity at 25 Amps and battery internal resistance I went with the cheaper branded Chinese AGMs at around 2/3rds of the cost. I guess only time will tell which of these scenarios is the most cost effective over time. I suspect of course Lithium is best but as I will likely not be alive by the time a Lithium battery dies - and due to the initial outlay, this has not been considered for my boat.
I'm hoping in my remianing sailing years that if my AGMs last 5 years, I need only buy one more set of batteries. Like I said at the beginning - what do folk think of Battery Cost Effectivness over time and the use of differing nominal system voltages and limiting voltage output in software?
I did not consider 36V, as chargers are not so easily available. It came down to should one use a 48V system for a 24V drive or just stick with a 24V battery system and buy a spare and separate switchable pack when funds permit? I guess the same goes for a nominal 48V system. 96V in series v 2 separate 48V packs in series. I don't favour non series systems. A personal thing I guess.
Another thing I believe I have come to realise is that the cheapest/most economical system is one where you limit the number of batteries to a series string for your system voltage, you maximise solar if keeping the boat on a mooring and if using 24V you have a Honda 1kW genny, 2kW if a 48V system. I f wishing to expand your system than a separate switchable battery pack which also give system redundancy seems to make sense.
Also due to the cost of marinasI found out it works out cheaper to charge batteries in the 50 to 80% SOC region on a mooring, as even with cheap electricity rates in a marina, by the time you pay for the marina you'll have spent less if you just do a bulk charge with a generator on mooring.
Also I don't know about other countries but in UK most marinas do a short stay (4 or 5 hours) for a recharge which is a nice compromise of cost v noisy or silent charging.
John
John.Rushworth.Com - Rushworth.Co.UK - Rushworth.Org.UK
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