T-Pain Is On A Boat: [Electric Boats] Homebrew BMS

Monday, November 4, 2013

[Electric Boats] Homebrew BMS

To change the topic a little.....

Since I will have an Arduino micro-controller on board, with Analog inputs, and options for a small LCD display (16 characters by 2 lines), and possibly even an SD card - it should be easy to set up BMS functions.

QUESTION:

In an IDEAL world, what would you like to track on a BMS?

I'm assuming a voltage monitoring pin for each battery.

I'm also assuming a shunt voltage input for each bank.

One could toss in a temperature probe for good measure.

The controller has a minimal time function to count the number of seconds since it was last reset.

All of this can be dumped to the SD card to pull up and plot power profiles later - for both charging and running.

And ULTIMATELY, it would be REALLY cool to add a GPS module so I could plot speed vs. power!!! (but that'll be a ways down the road...)

Aside from battery voltage, current, time, and possibly temperature - is there anything else a BMS should monitor?

John

From: oak <oak_box@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Monday, November 4, 2013 4:37 PM
Subject: Re: [Electric Boats] Battery Charging Basics - homebrew chargers

Mark,

From what I'm seeing, it looks like if you're going to provide a "constant current", you're basically providing a variable voltage supply that responds to the drop across a current limit resistor.

There doesn't seem to be an EASY way to support a wide range of voltage from 36 to 144V.

The microcontroller part isn't so bad. I've used a number of different ones in the past. Latest experience was with the Athena. I think the Arduino was coming out toward the end of when I was messing around with the Athena chips - but they were prohibitively expensive.

At this point in time, the Arduino system has matured a LOT. You can get a basic board for $30. With that, and a USB cable, you can download the IDE and start playing. The IDE (programming environment) is pretty simple to use - I won't say "EASY", but it's much better than I've seen in the past. Just a few quirks. The BIGGEST PAIN I've had with the Arduino is getting new laptops with Microsoft 7 to find and use the drivers. Microsoft - ARRRRRGH!!!!

Anyway, the Arduinos have at least 6 analog input ports (depending on which specific variant you get), and a number of different digital I/O ports.

They have a number of nice built in functions - like floating point math - that makes life simpler for things that you want to be user friendly. These controllers should work very nicely for charging and even battery monitoring.

John

From: Mark F <mark.internet@yahoo.ca>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Sunday, November 3, 2013 2:46 PM
Subject: Re: [Electric Boats] Battery Charging Basics - homebrew chargers

I would like to help, if I can.
I would like to see a charge profile for NIMH batteries as well.
I think it would be good to be able to charge and monitor multiple banks.
It would be good to have a design that supports many voltages, IE 36,48,72,96,144.

I have some experience with microcontrollers from years ago.
What type of circuit would you use for the constant current supply?

Mark

From: Kirk McLoren <kirkmcloren@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Tuesday, October 29, 2013 12:32:40 PM
Subject: Re: [Electric Boats] Battery Charging Basics - homebrew chargers

hard to get into trouble with a trickle charger.

On Tuesday, October 29, 2013 11:41 AM, oak <oak_box@yahoo.com> wrote:

I hope this will be both fun and educational....

I'm trying to build a small, home brew battery charger. From what I see, it sounds like the primary difference between FLA, AGM, and Li batteries (from a CHARGING) perspective is the charging profile - notably, the voltage level of the charge.

Granted, if you're trying to do a FAST charge with lots of amps, there are a lot more details to worry about. But given the limits of readily available parts, I'm looking at 1-2 amps charging current - so I think I can simplify things a LOT.

It sounds like building a "constant current supply", attaching it to the battery (at 1-2 amps), and monitor the battery till the battery voltage comes up to the prescribed level, then disconnecting the current source.

According to the Battery University (http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery), it looks like I can use a constant current source for the primary charging (stage 1), then maybe connect to a regulated power supply for the topping charge (stage 2), and then use a small microcontroller (Arduino) to monitor the voltage over the next few days / months, and occasionally turn on the "float charge" voltage for a couple of hours. (stage 3)

Does this sound reasonable?

For charging Lithium batteries, is there any difference, other than paying a LOT of attention to the voltage levels for the peak charge level?

From the BatteryUniversity.com site, it sounds like charging Li batteries to 4.1V per cell, and stopping there will extend the life of the battery bank, and provide a bit more guardband to avoid problems.

Thoughts?

Thanks!

John