T-Pain Is On A Boat: Re: [Electric Boats] Re: Planning Cal 2-27 conversion, advice needed

Saturday, November 17, 2012

Re: [Electric Boats] Re: Planning Cal 2-27 conversion, advice needed

Myles.
Nice to see a post from yourself.

I think you were the one that really inspired me to build me E Boat!

By the way, it's not a sail boat and it runs flat out most times.

To the naysayer, you rely on that old ICE unit and see where it gets you during the zombie apocalypses!

mattelderca

From: Myles Twete <matwete@comcast.net>
To: electricboats@yahoogroups.com
Sent: Saturday, November 17, 2012 2:50:46 PM
Subject: RE: [Electric Boats] Re: Planning Cal 2-27 conversion, advice needed

@Kotyari asked several questions:
"Can a battery pull all 35Amps in bulk mode? If it can, that could trip the genny, making it impossible to recharge batteries with less than %50 left. I suppose disconnecting one converter would fix that, but that seems like a kludge..."
Of course it depends on the battery----check the manufacturer's specs. Assuming a lead acid battery on the order of 200ah, the manufacturer might spec 20%C for charge rate (i.e. 40amps), however that isn't what the "battery can pull". The fact is that you could pump 0.5-1C or more into a flooded battery during bulk charge just as you can pull 0.5C – 1C , especially from good AGM or Lithium batteries. My electric car pulls up to 1C from the batteries and regenerates at up to 1C. So you could conceivably pump 100-200amps into a 200ah battery during bulk mode (assuming internal resistance is low enough---there's the rub). Hope this helps you understand.
"So, if a WFCO can provide 35amps, that current will be split between the battery and the motor, so in effect it doesn't matter how low you set the throttle, it'll still draw 35amps. Another question is how much of that power will go to the motor when both it and the batteries are drawing. I'm guessing the motor will have first dibs, since it's probably lower resistance?"

As current goes to the batteries instead of the motor controller, the pack voltage rises. As that happens, the charger voltage also rises and if that voltage gets near the voltage where the charger transitions into CV mode instead of CI mode, then the charger will "throttle back" its current. As this continues, the charger delivers less overall power, the genset delivers less power and slows down (if in Eco mode). To avoid this and to maintain constant maximum from the genset and steady power to the system, I often set my throttle based on "Neutral net current" into the battery pack---i.e. at zero throttle I see my gauge indicating 40amps going into the batteries. As I increase the throttle, the net current to the batteries drops---I keep increasing throttle until the net current into the pack is zero or negative (i.e. all genset power going into motor/controller).

" I supposed it would be ideal if a 35amp converter could be specifically set to be limited to, say, 25amps. That would allow Honda to operate at its rated continuous 1.6Kw and leave a margin on the converters. Is there a way to do that?"

Exactly. My Lester will deliver 20amps, maximum, period. And since I knew with a 2^nd charger I could deliver up to another 20amps, I might be able to add another Lester, but they are bulky and not super efficient. And since I didn't need a 3-stage charger for cruising with a genset, I opted to use one of my Vicor Megapac units and load it with 48v/4amp modules. Initially, I loaded 8 of them for 32 amps. Well, that plus the Lester pulled the Honda to its knees…so I removed one of the 4amp modules, now attempting to deliver a total of 48amps into 36v (1768watts). That also brought the Honda into overload pretty quickly. I tried 6 modules and found that it worked for a few minutes (44amps into 36v total), but then again, overload. Finally, I was able to use 5 modules that delivered 20amps from the Vicor so that I can run steady with 40amps into 36v (1440watts total).
IN case this helps…

-Myles Twete, Portland, Or.