hobbycity lipo with smart bms shopping list

[auraslip]

I'm considering building a 12s3p pack out thesecells on sale for $7 each. It'd be 44.4v 6.6ah for ~$90

I want to use one of these "smart" bms,and one of these chargers. $50

(After shipping that is only slightly more than a similar sized SLA pack!

bmsbattery.com will program the BMS and charger to what ever settings you want. What settings do should I use for this hobbycity lipo?

Before anyone says anything about the 10/20 amp limit of the BMS: I will follow hal's advice

I use to buy bms according to current that I use. Now I take the smallest current BMS and connect exit from bms to small power of controller and big wire from controller is connected to battery pack directly via fuse. when bms shuts down it does not cut off main power suply, just controller power.

Also, this is my first time with lipo: what connects and cabling will I need to set this up?

 

[dogman dan]

I know you are not made of money, but you will be looking at a lot of wiring. If you just solder it all permanently though, you only pay for some solder, and Whatever permanent connector you use on the main + and - wires.

So cut the wires on the three packs to be paralelled and solder them all together matching up the wire colors so you have one balance plug and a discharge plug. Then you will need to make a wire to your charger that matches the discharge plug. that's it.

The discharge plugs will have to be a kind that can be seperated, so you can series connect em without adapters. so bullets, andersons, or even spades with insulated covers.

Far as I know you are pioneering this use of the bms and charger. Good luck, and run it outside. I'd want a lipo charger myself for it, and then paralell all three sections of the battery to charge it. You could just build the paralell adapter into the charger wire, and do non balancing charging easy.

I'm just a fraidy cat, so I use the real lipo chargers. Then I can charge inside on the fireplace tile hearth.

 

[auraslip]

Thanks dogman,

Far as I know you are pioneering this use of the bms and charger. Good luck, and run it outside. I'd want a lipo charger myself for it, and then paralell all three sections of the battery to charge it. You could just build the paralell adapter into the charger wire, and do non balancing charging easy.

at the least I'll charge it in one of my big pots with a brick on top 8)

 

[auraslip]

I think DoctorBass has the white paper with the testing that showed the 10x increase in lifespan from using a 4.1v cut-off. It has caused me to set my cut-off voltage to 4.1v rather than 4.2-4.25v.

- lfp

Lipo Nominal 3.7v per cell
Manu Spec Max Charge: 4.20v per cell
Suggested Max Charge Cutout: 4.18-4.15 (should extend the life of your packs)
Maximum Low voltage cutout: 3.0v per cell
Suggested Low Voltage Cutout: 3.1-3.2v per cell

- mwkeefer


I'll go with 4.1v HVC and 3.2v LVC. This should provide a good %20 - %80 SOD - SOC that should extend the life of the cells. Also it should provide some protection from over/under charge should the BMS fail.

I'm pretty ghetto with expressSCH, so forgive me. File for modification here.

Can't figure out where the "ignition wire" goes...

 

[dogman dan]

FWIW, i rarely let my lipo get below about 3.75. That's when the lights begin to flash on my lv warnings. At 3.5 they start chirping at me. From 3.5 to 3.0v takes very little riding, so pay a lot of attention to your voltmeter when it gets to 3.5. Because you are seconds from disaster by then.

If I screw up, and misjudge my ride, I can milk that last quarter volt from 3.75 to 3.5 quite a distance, up to a mile. But below 3.5, more like a block. Below 3.5v, there is virtually nothing.

 

[auraslip]

You're right Dogman. I've done a little bit more research.

At 3.5v it dives, as you say. These graphs show a bit of difference in regards to the 10c and 7c rate. Somewhere between 3.55v and 3.75 seems like a good point for LVC. Probably 3.7v LVC, and 4v HVC.

 

[dogman dan]

I refer to 3.75v when resting too, btw.

Under load, I will start to see the warnings flash when pulling max amps, then go back to steady on while I still have several miles of riding left. Yesterday for instance, the lights began to flash while I was still 2 miles from home. No prob. I backed off a bit on the throttle, and rode home. when I got home, the batts were still just about 3.78v each at rest. At no time did I hear beeps telling me I had gotten below 3.5v even under heavy load. I often return to the house and find the batts still at 3.9v after stitting 5 min.

 

[auraslip]

So I've been doing a little bit more research. I found this book: http://www.amazon.com/Battery-Management-Systems-Large-Lithium/dp/1608071049
The google books preview looks good, but it's priced like a college textbook.

TheEthileonsite has some pretty useful BMS info for noobs.

Anyways. What I'm concerned about is the charging. How does the BMS interact with the charger? When the first cell hits HVC, the BMS shuts down the charger(how?) Then it brings that HVC cell down to the lowest cell, and the charger starts up again. Repeat until all cells reach HVC.

And about the charger; It's probably has a voltage adjustable pot inside it. How does that effect cc/cv? Does the voltage I set effect the CC phase or the CV phase?

I'm determined to figure this all out because it seems their is a huge gaping need in the community for a LIPO bms. Maybe I'll buy that book, some extra bms, and the BMS programming cable.

 

[Gow864]

Glad you're doing this auraslip. I've often wondered why it hasn't been done before. I'll follow this thread with interest.

Gow.

PS: Each packs balance wires have a neg wire coming out of them, I guess you'll only use one of these to connect to the BMS? Which one? the first packs or last? (Demonstrating how little I know about lipo packs here)

 

[cell_man]

The BMS has a few parameters that can be set WRT charging:
balance voltage - voltage at which the shunt is introduced (typically about 100mA or less on a small BMS, maybe 200mA on a bigger scale BMS), typically 3..6-3.7V for LiFePO4
HVC- voltage at which the charger is disconnected from the pack, typically 3.9V for LiFePO4
HVC release voltage - voltage at which the charger is re-connected to the pack, typically 3.8V for LiFePO4 BMS

BMS will not bring the highest cell down to the lowest, it will cycle any high cells between HVC and the release voltage until the low cells come up in voltage. If you have a well balanced pack made with well matched cells the BMS should keep them balanced and also protect any less than perfect cells from hitting a dangerous voltage.

 

[auraslip]

I don't what WRT charge is, but I assume it's the program.

These guys http://endless-sphere.com/forums/viewtopic.php?f=14&t=20971&start=0
are using this to program their bms http://www.totalphase.com/products/aardvark_i2cspi/

Not cheap, but probably better than the one bmsbattery sells.

As cell_man pointed out, there is more than just setting the HVC and LVC. Considering this is a very DIY application, I wonder if the programmers at bmsbattery will set it correctly for lipo.

 

[auraslip]

So I'm going through with this. I'm building up a bike to be a test platform for this project. I'm gonna start with a bms, 600w charger, and a 12s 10ah lipo pack. battery stuff should cost ~$300.

I'm gonna get this Cell-log voltage monitor http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9282

I've heard hobby city has qc issues with lipo. I'll monitor after the break in cycles to make sure everything is good.
I also need these as a lvc and hvc alarms. I can watch the voltages drop as I ride, but I need to make sure the charger and BMS works when I'm charging the pack.


I know the difference between cc and cv charging, but I don't know how or why they switch. I need to read up more about it, because I'm sure I'll want to double check BMSbattery.com's work.



Not related, but I'm also gonna get this temp alarm http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9744
Charger is gonna be in the battery box, and I don't want it to over heat.

 

[auraslip]

I got the charger end figured out

CC: Battery charges at a constant current ( a 5 amp charger charges at 5 amps.) This goes on with the voltage of the pack rising until
CV: the charger then goes into constant voltage. This holds the voltage the same while the current gradually reduces. When the current gets to %6 or %10 of the chargers output power (for example a 10w from a 100w charger), the charger shuts down.

While that is going on the BMS is also functioning. More on that as it's a bit more complicated and dependent on the bms.

 

[snowranger]

I like that idea about using the bms only for lvc to the controller. Good luck with the smart bms. If it works, that will make lipo way more user-friendly.

 

[chroot]

HI- I tried check BMS Battery site your link show up Phishing site alert by OpenDNS.

Here picture.

 

[Erikjan]

The smartbms works ok for Lipo i use it for 2000+ km and am happy with it.
I have 13s 16Ah Lipo battery (the cheap 4000mah ebay cells) and a 2,5A charger 48V ebay charger.
BMSbattery program the smartbms @ lvc 3V hvc 4,2V.

I think the battery is not 100% full when stop charging the cell voltage is 4,08V for me is ok.
I only use 8Ah for me daily trip. never had a emty battery.

I check the voltage from cells after a 15km trip low cell 3,82V high cel 3,84V most cells are 3,83V.

My bike is a low power bike only 7 ~ 10A max. @ 30km/h

Some pictures from my bike.
http://www.dropbox.com/gallery/11713634/1/ebike?h=83a4e9

sorry for the bad spell

 

[snowranger]

How does the wiring work on this? Isn't the positive directly connected to the battery and only the negative attached to the bms?

I use to buy bms according to current that I use. Now I take the smallest current BMS and connect exit from bms to small power of controller and big wire from controller is connected to battery pack directly via fuse. when bms shuts down it does not cut off main power suply, just controller power.

 

[auraslip]

How does the wiring work on this? Isn't the positive directly connected to the battery and only the negative attached to the bms?

There are some wiring diagrams on the bmsbattery website that show you the proper way to wire the bms, but it only is good for 10 amps.

The idea is to figure out a way to bypass it, and just use it as a lvc/hvc that can cut power to the controller through the ignition wire or brake line.

 

[Erikjan]

There is a little problem that when controller ignition switch is of there will be a little current.
The risk is if you don’t charge or forget disconnect the battery it will go to empty.
Maybe it is possible to use a big relay connect to the bms.
I don’t have that problem because I order the 20A smart bms and my bike is only 500Watt

 

[auraslip]

The thin red controller "ignition" wire only draws 60 ma. A simple toggle switch can be used.
The thick red wire is the MAIN POWER to the mosfets. This is the power that makes the motor run.
The MAIN POWER wire can be connected all the time. When the ignition is off, the MAIN POWER current draws less than 10 ma.
The MAIN capacitors in the controller will stay charged for a long while even after the MAIN POWER is disconnected.

10*24*7=

That is 1.68 ah a week, so it'd take a while to discharge a battery.

 

[auraslip]

you could use a few of these to charge lipo http://cgi.ebay.com/5-15-VDC-Over-voltage-protection-project-kit-hobby-/140334725309?pt=LH_DefaultDomain_0&hash=item20ac99f8bd

Just hook the relay up to the charger - mains connect. lol. Ghetto fab.

 

[auraslip]

k

 

[auraslip]

erikjan, thanks for posting pics of your bike btw!

 

[auraslip]

I e-mailed jack at BMS battery about setting the smart bms and charger up for me!

Once I hear back I'll fire away!

I've set up about $150 worth of connects, wires, and chargers from HK. Running lipo on an ebike ADDS UP. It doesn't help that HK doesn't describe their products or what comes with them very well at all. ERHG. And everything you need is in back order. Frustration.

I've settled on a 10s2p lipo packs of 5s 5ah stuff from the us warehouse. With this I have enough range for my commute to school, and I can series it all up to test how fast my bike will go at 20s.

I'm a little concerned about safety because I'll be carrying around the bmsbattery charger in the battery box so I can charge at school. I'll need to fireproof the inside of the battery box just for safe measure. You think tinfoil hot glued to the inside will work? In any case, I'll be monitoring the pack very carefully during the first dozen cycles or so. Got a cell log ordered too.

 

[johnrobholmes]

How about programming it with one of these? http://www.robotshop.com/devantech-usb-to-i2c-module.html?utm_source=google&utm_medium=base&utm_campaign=jos