Luke-
Regarding generating while cruising, the answers depend on your system components, configuration & whether all the power from the charger is going to the controller or whether some is going to the battery. Assuming your charger isn't "too smart", then it won't 'overthink' what's going on, e.g. if in constant-current mode & the pack voltage is dropping instead of rising. You can imagine that the charger could have failure detection in place that in that scenario might just stop charging. So what you need is a charger that will accept these scenarios and still keep dishing out maximum power:
· Load voltage dropping despite full power being delivered
· Load voltage increasing towards the CV setting for the charger, but batteries still can handle full current
· Load voltage static
In my case, I use a Honda 2kw quiet genset. My charger has been a Lestronic golf cart ferroresonant charger. This charger has no problem delivering steady output for voltage static or dropping, but it does ramp current down earlier than I'd like on a rising voltage. This config is good to 720watts or so of output into the DC bus. When I want to deliver a steady 1.4kw into the bus, I parallel up a home-configured Vicor Megapac power supply loaded with 5 modules rated at 48v/4a each. In that scenario, I could get 40amps continuous at 36v into the DC bus. For all-day cruising, I'd then set my throttle such that "net draw" from the batteries is measured as 0amps on my Link10 meter. At that point I know that the pack isn't being drawn down and all the power is being sent to the controller. Now, if doing this at the beginning of a trip when the pack is already near full, it's best to set the controller speed to draw MORE power than the charger is supplying otherwise you could find out much later that your genset hasn't been delivering the power you thought it was all that time. Always check the battery voltage and the net current going into it periodically to see where things are going.
By doing your calculations ahead of time and during your trip, you can cruise conservatively with your power, then as you get closer to your destination you can open it up more. On longer trips, I typically motor out of port on electric, then once out on the river I get the genset & charging going as I need, making sure it's all steady, then run it that way for hours until I get to the point where I know I can make it with 1 or 0 chargers, then let the genset work less for awhile then turn it off, cruising into town with batteries only.
I have some experimenting to do now that I've switched from 36v PbA to 32-48v Lithium. Happy motoring.
-Myles Twete, Portland, Or.
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of luke.wolbrink@gmail.com
Sent: Friday, January 03, 2014 6:19 AM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] DIY Hybrid System Questions
I'm in the middle of converting my 1971 Tartan 27 over to electric (22'LWL, 8.5'Beam, 7500#displacement, 5kw bldc motor w/2:1 reduction) in Chicago on Lake Michigan. I'm beginning to run out of funds for the project and am well short of my 200AH LiFePo4 battery pack; currently 72AH. Since the boat is primarily a daysailer with the motor being used for in/out of the harbor and perhaps to motor in if the wind dies and I have a schedule to keep; I figure that 72AH will be fine. I would however like to be able to go on longer cruises like a lake crossing or a trip to Milwaukee; to do so I would feel more comfortable with a greater range on my motor. I'm considering a setup with a small gas generator (2kw max) that hooks into my shorepower plug and powers a 48v switching power supply (1kw) that will drive the motor at a low speed for some extended range. Now for the questions:
1) When on the power supply can I run on batteries as well or is there concern about backfeeding and damaging the batteries?
1a) If it's ok to run both at once, can I charge my batteries with the normal charge hooked into my shorepower system and run them at the same time for a few more watts of power?
2) With a switching power supply can I get away with a standard hardware store generator or will I need to get one of those pure sine-wave generators?
3) The cost for power supplies goes up sharply after 1kw, about what speed could I expect from 1kw of power with my 13x8 2blade prop? (I know the prop isn't ideal but again the budget is tight and I'll need to stick it out)
4) The longest run I need to make is up the Chicago river and through the locks. This is about a 5mile trip at pretty low speeds (2kts) and little current, will my 72AH make it? If not I'll need to hurry up and make the hybrid a higher priority.
Thanks in advance,
Luke
| Reply via web post | Reply to sender | Reply to group | Start a New Topic | Messages in this topic (4) |
No comments:
Post a Comment