Regarding the mini bms for marine use: I have been using one as described by Dave in my runabout for a couple of seasons to manage my 60v 10kwh LiFePO4 bank. It works fine. Just take sensible precautions about keeping it and batteries dry.
Ned
On Jun 12, 2013, at 10:11 AM, Dave Steere wrote:
My own home made EV uses a product called "mini bms" to manage a bank of LiFEPO4 batteries. It consists of what the designer calls a "head board," really just a small printed circuit card that monitors the "loop." The head board is buried somewhere under the dashboard.The loop is a continuous 18 ga wire that interconnects terminals on all batteries in the pack, in my case, 36 of them. Each cell has a small pc board attached to its terminals. Mounted on each of these mini pc boards is a green LED and a red LED. Green indicates "normal" or voltage between about 2.7 and 3.65V (different boards for different brands and capacities of lithium cells on the market). Each mini board also monitors current, temperature and maybe a few other parameters. It provides a short between its loop terminals when all conditions are normal. The loop of wire that interconnects all these mini boards has continuity when all cells are showing a green LED. If you run the pack down to a point that one cell experiences a low voltage alarm, its green LED goes dark and a few seconds later, the head board registers an audible alarm. Red LED's on each cell indicate that the cell is approaching a high voltage which, if allowed to continue, could damage the cell. If the voltage climbs a bit higher, a signal is sent to the battery charger (can be an electronic switch, a transistor, or a relay) which shuts off the charging process. The audible alarm is also activated. So if you are driving and hear a piercing 1Khz alarm, it's time to pull over and get a charge. No, one doesn't have a nifty LED display on the dashboard to show which cell is low, but it's usually not too hard to pull over, remove covers to the battery box and look for an extinguished green LED. This product can be researched and purchased at this address: www.cleanpowerauto.com/MiniBMS.html .The inventor, Dimitri, responds quickly to e-mail inquiries and is really quite helpful. I have found that this form of BMS is a lot cheaper the full up BMS products available commercially, and while it is still necessary to do a few cell by cell measurements with a multimeter, that isn't too onerous. I can't think of any reason why this "mini BMS" approach wouldn't work just fine in a marine environment.
On Tue, Jun 11, 2013 at 8:22 PM, Kirk McLoren <kirkmcloren@yahoo.com> wrote:
Electronics with each cell, yes.
From: Roger L <rogerlov@ix.netcom.com>
To: electricboats@yahoogroups.com
Sent: Tuesday, June 11, 2013 12:07 PM
Subject: Re: [Electric Boats] Re: Battery charging questions...
I would assume that something like this is what Tesla is doing with his cars - monitoring and charging each cell individually. Does anyone know?Roger L.----- Original Message -----From: Craig CarmichaelSent: Tuesday, June 11, 2013 10:44 AMSubject: [Electric Boats] Re: Battery charging questions...Hi,
You can simply recharge your 4 batteries individually, one at a time,
with a 12 volt charger. It's a rare charger that has a grounded DC
side, so normally the DC output just floats at whatever the voltage
of the particular battery is. When the green light comes on, move the
charger to the next one until they're all done.
--- To expand on that theme... ---
I got an electric car with no batteries a couple of months ago.
Usually battery balance is a big thing, and when some of them start
getting low, the entire set is replaced with brand new identical
batteries, costing 3000-4500$ for lead acids. Hopefully that's less
than you would have paid for gas for the same driving, but it's all
at one crack. (That's when you can get an electric car cheap.)
But the whole problem arises because of charging them all as a series
string with one charger. For that, they all need to be in 'perfect'
balance.
I'm charging each one separately with individual 12 volt chargers.
That way, none affects the other during charging and any motley mix
of batteries can be used, even mixed chemistries. Range is of course
limited by the weakest one, so some sort of balance is desirable, but
it doesn't have to be 'perfect' like with one series charger.
--- My Individual Battery Monitor System project ---
Especially with a higher voltage system like the car, care must be
taken not to drive the weakest battery(s) to death before noticing.
To that end, I'm making a microcontroller based battery monitoring
system that measures every battery. The display will show each one
with a separate bar graph. As a battery gets lower, its bar will turn
from green to yellow, and then to red. There'll also be an audible
warning at those points. This frees the driver from having to
manually check batteries with a meter (ever!) It'll also be obvious
which battery(s) to replace if the range is too short. (I hope to
sell these once they're working well.)
--- My batteries & chargers ---
In the car I have new lead-acid batteries, reconditioned batteries,
an old battery with lower capacity that I'm going to replace soon, a
nickel-metal hydride battery in 6 stacked trays of 10 D cells (12V,
60 AH), and three nickel-metal hydride batteries in 1-1/4" irrigation
system PVC plumbing pipes, like giant flashlight tubes.
I'm using 5 amp power adapters producing a constant voltage float
charge with resistors (eg, .5 ohms) to limit the current. For the
lead-acids, the float voltage is 13.8 - 13.9 volts. For the NiMHs,
it's 14.00 to 14.05 volts (it's fairly critical with them.)
Obviously, with the resistors, only a low battery will draw 5 amps,
eg with .5 ohms, it would draw 5 amps if it was 2.5 volts below the
float voltage, or 11.3 volts for a 13.8 volt charger. That protects
the 5 amp power adpater chargers and if a battery doesn't want to
come quite up to the float voltage without drawing excessive current,
the current it draws allows it to sit a little lower drawing a little
current.
This is a very slow charging system that takes many hours to finish
topping up the batteries, but also the gentlest, so I hope to get
extra long battery cycle life.
For 10 of the power adapters I changed a resistor inside that brought
them from 12.0 volts to 13.8 or 14.0. For the 11th one, I bought a 15
volt adapter and along with the current limiting resistor, I put two
diodes in series. Since the diodes have a .6 volts forward drop each,
the 15.0 volts is reduced to about 13.8. (I curse myself for only
buying 10 of those adapters when a store had them for 3.95$. The
extra one for the 11th battery was 28$.
--- The Mn-Ni Test Cell ---
BTW: The new Mn-Ni cell isn't looking very good at the moment, but
I'll charge it another day or two before jumping to conclusions. It
charges to about 1.9 volts, but is having the same problems as my
Mn-Mn cells.
Cheers,
Craig
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All the best,
Dave Steere
dcsteere@dcsteere.com
850-234-2540 office
850-319-6010 cell phone
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