With or without a BMS, you'll probably want some sort of Ah or Wh counter. I use a LinkPRO. With it I know the number of Ahs still required to reach end of charge cycle, and what the total pack voltage is as I near the end of charge. When underway I always know how many Ah I have available. Best fuel gauge ever.
With the Ah counter on board, I never operate near the extreme ends of the cells' capacity. As a result, my cell level BMS has little to do. It was reassuring to have aboard when I was getting familiar with these cells, but once initially balanced, I don't use the BMS for shunting charge current at all. But it is kinda cool to watch the bar graph display of all the cell voltages and temps moving around as I motor around.
Since my Elcon charger has a higher cutoff voltage then I prefer, I terminate charging by using the Ah counter to monitor the total pack voltage, and also the Ah remaining to reach "full". If the LinkPRO goes nuts during the charge cycle, the BMS will kill the charger if any cells get too hot or too high voltage. If the BMS also pukes, the Elcon will still terminate the charge safely, using its own charge profile. I have even been thinking about a wall timer to be DAMN sure.
Yes, I like redundancy when dealing with shutting down the charger. There have been too many unexplained lithium EV fires.
-Tom
--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> wrote:
>
> Hi Steve,
>
> Most of the EV guys are still running DC motors where volts equals RPM, but some of them are pushing the limits of those motors. Looking at the Warp DC motors, the accepted voltage limit seems to be around 170V, even though the specs say 192V. Most of the better DC controllers limit the voltage appropriately. For AC motors, the controller really manipulates the voltage as well as the current, as long as the controller can accept the pack voltage, you should be OK.
>
> But it's really amps that one needs to be worried about. Since the amps vary depending on the throttle setting (even for us boats) you just want to keep your amps within spec for the duration that you expect it. Cars can pull 1000A or more for just a few seconds, as long as the controller can allow it, it's then up to the motor to survive the current. A liquid cooled Zilla 1K controller can push 950A at 200V, but it's continuous rating is 300A at 100% duty cycle and 50C coolant temp.
>
> On our boats, peak capabilites are much less important than in a car. Like you said, we operate in a much more continuous mode. But few of us operate at throttle that would drain our batteries in less than 45 minutes (about 1C). It's easy for us to carry extra weight, in a car, the battery weight can really impact performance. So some car guys look to smaller cells at higher voltage. Since Li cells can often take loads of 4C or more, they can get away with it. But that's just not a factor in our marine installations (well maybe for a drag boat).
>
> My 48V nominal system rests at almost 53V, and peak charging voltage is about 61V. So all of my components are rated for that peak voltage. My Sevcon Gen4 G4845 has a max operating current of 69.6V and a continuous (1 hour) rating of 180A. At full throttle I pull 110A so my boat is well within the opertaing limits. The two minute rating of 450A is interesting, but of no practical importance to me. The ME0193 PMAC motor is rated for 96V nominal so it probably can take somewhere around 110V, but the amps are the important part. With a 1 minute rating of 420A AC and a continuous rating of 125A AC, it's still all well within ratings at max throttle in my boat. Motenergy says that max winding temp is 150C, in my boat running at 105A for 30 minutes yielded winding temps of less than 85C and when I slowed down to 80A, the motor started cooling itself down. So the motor is sized fine, even with my "high voltage" 48V system.
>
> I believe that your boat is running Solomon drives. There is not much technical info on the web anymore, but I did see that they are rated for 144V nominal (12 x 12V batteries) Since we know that regular lead acid batteries charge past 14.5V (14.4V peak for AGM), You said that your peak voltage is 174V. Switching over to Li batteries, 48 x 3.2V cells have a niminal voltage of 153.6V. If I triple the resting voltage of my 16 cell pack, I would expect your resting voltage to be around 158V. Using a maximum charge voltage of 3.8V/cell, the max system voltage would be 182V, but it's your choice when it comes to a charging profile. Many Li owners use charging profiles that stop at 3.6V/cell which puts your max voltage at 172.8V, exactly the same peak voltage as an AGM battery pack. BTW, CALB cells have a charging voltage cutoff of 3.6V, so a 48 cell pack will be fine with all of your existing equipment.
>
> Other people use 45 cells, at 3.2V nominal that's 144V. using a 3.8V charging cutoff, the max voltage would be 171V, definately within your systems ratings. You need to find out the max voltage that your controller and your Li cells can take and base your new battery pack accordingly.
>
> As far as BMS, some folks believe that they cause more problems than they solve, but I'm not in that camp. That said, once your pack is balanced, there should be little drift for hundreds of cycles. When I first put my pack together, my BMS modules came into play every charging cycle as the cells were brought into balance. Now, the modules really don't do much, but I like to keep them there, just in case. The more consistently you treat your batteries (like on a boat) the less that they will drift out of balance. Realistically a small 1 cell charger applied manually to each cell in a bank will put a bank into balance. If done as regular maintenance, like every 6 months or 100 cycles, which ever comes first, a BMS will do very little for you in regular operation. A BMS can protect your bank in the case of a failure (wild charger, deep discharge with a non-functional generator) preventing permanent damage to one or more cells. It's your money, it's your call.
>
> Fair winds,
> Eric
> Marina del Rey, CA
>
> --- In electricboats@yahoogroups.com, Steve Dolan <sdolan@> wrote:
> >
> > This is probably to Eric but anyone with input is welcome.
> > I have been at the Car forums mentioned and been looking at the replacement to my AGM's in hopefully a few years. At the DIY Car forum there are a few things I don't understand that may or may not apply to a boat.
> > In most cases the car is going to very in speed a lot more than a boat. Our usage maintains a rather linear use therefore a steady decrease in power over time. On the other hand a car starts and stops, coasts and accelerates much harder than a boat will see.
> > It seems that Car battery LiPo4 packs are exceeding the rated Voltages of the motor. Probably not the motor controller to a certain extent or damage would occur but it seems that people are adding batteries 10% to 15% above the rated pack voltage. A 48V pack may be increased to say 56V of batteries. I know that I bulk charge my AGM 144V pack to 174V. What is the thought behind this increase in batteries?
> > The Selection of Amp Hours seems to be all over the place. I see people buying 100AH batteries at a C4 or higher rating. Wouldn't the average boater be fine at a C1 Rating and 200AH batteries? Our discharge rate wouldn't be as high as cars since we wouldn't be drag racing the boat (At least not mine) and I tend to max out at 50A at the 144V. I must be missing something here.
> > As far as BMS's go, again we tend to be more linear in use and abuse. Since a lot of people are saying for a car BMS may not be necessary wouldn't this be more true with boats?
> > And then in general, what would differentiate a car pack from a boat pack in selection of batteries or for that matter even equipment when it comes to LiPo4's?
> >
> > Thanks for your help on this.
> > Steve in Solomons MD
> > Lagoon 410 SE
> >
>
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