DIY Lithium Packs, Proposal and Discussion

[luthj]

I have been considering a DIY LiFe battery pack for my van. Something in the 200-400AH range @ 12V.


Quality cells seem to be available from CALB, Fortune (frey) etc. A user on ExPo recently ordered 16 100ah cells factory direct from Frey. Only $1600 delivered, and came with factory test reports.
https://expeditionportal.com/forum/...tteries-vs-drop-in-replacements.198005/page-4

I have an existing electrical system consisting of Outback inverter, Solar CC, Mate, and FlexnetDC battery monitor. This system is not super configurable (unlike Victron), but it can be programmed to charge lithium batteries suitably.


My major needs to build a diy pack, are monitoring system with cell voltage and temp monitoring. One that can trigger a pack disconnect. Likely a gigavac latching relay, or their high efficiency NO relays (0.3A at 12VDC).

Anyone have a suggestion for a reasonably priced BMS that can provide temp and voltage disconnect? I don't need remote monitoring or a fancy screen, just a last case safety system.

Balancing would be nice, but is not required. If I feel its necessary, one of these 4s balance boards would do the trick.

The Orion Jr BMS would meet my needs, but is pretty pricey at ~$550. It has lots of functionality that I don't need. Regardless the BMS must have programmable setpoints. I could rely on the active balance boards, and just use a pack level disconnect, but that creates a single failure point that is not protected.


I found this utility oriented stand-alone BMS. 552$ plus wiring harness. Can handle up to 12 cells. Passive balancing up to 300mA, 4 contactor driver circuits, and 8 temperature probes. A built-in ethernet port can be used to program the unit, and the software seems quite flexible, if a bit difficult to learn. Lots of options I don't need, but programming via ethernet has its appeal. It looks a lot more flexible than some of the other options. Pretty similar to the Orion Jr.

It also has a modbus and CANbus2.0 ports...

https://nstore.nuvationenergy.com/c...voltage-bms-battery-controller-kit-12-channel
https://www.nuvationenergy.com/site...-Low-Voltage-Battery-Controller-Datasheet.pdf




This would yield a pack with much higher peak current than the drop-ins with solid state relays. Though the trojan units with normal relays would be about the same. Those are around $1k per 100AH. For a DIY route $1600+$700 in materials would yield a 400AH pack with much higher rates. If a cell fails, it can be replaced without trashing the whole pack.

The primary goal is for this to be the last pack this van will ever need. I don't want to be dependent on some untested (though likely reliable) electronics buried in a 1000$ battery. I don't want the complexity and issues that come from having 2-4 parallel BMS. The Tesla modules are nice, but I don't want to completely rework my electrical system for 24VDC.

 

[luthj]

Here is another BMS. This one is simpler, costs about 400$. Looks like it supports an external shunt, as the internal one is limited to 75A.
https://www.electricmotorsport.com/emus-bms-mini.html
https://emusbms.com/wp-content/uploads/2018/10/EMUS-BMS-mini-User-Manual_v0.8.pdf
https://emusbms.com/product/bms-mini

 

[hour]

I haven't much to add, but I installed the balancer you linked on my 4x3.2v 90ah battery setup last night. It definitely works, I have an additional harness for monitoring... but good grief the noise. My cells are off by like .003 and yet it continues to work, producing the most irritating high pitch sound that penetrates everything in my house.

 

[LeishaShannon]

Can I make a suggestion?
Forget about a BMS and just use a Victron BMV to monitor the midpoint of the pack. Periodically (I do it less than once a year now) use a celllog8 to check cell balance and manually balance if required. Manual balancing can be as simple as using a long extension cord that you probably already have as a high power resistor.
Stay out of the knees , ie. stay between 3.1vpc - 3.45vpc
My batteries are 5 years old, 4 years of full time electric only travel (oven, induction hotplates, reverse cycle AC, hot water, etc) , and have seen ~7 megawatt hours of energy through them. Thats equivalent to ~900 cycles to 100% DoD. I did a capacity test last week and got 94% of the original capacity back , they're a little out of balance so I'd guesstimate I can get another few percent out of them with a balance.

 

[jonyjoe101]

I been using the delgreen 4s active balancers (balances at 6 amps) for almost 2 years and they have been perfect. I don't notice the high pitch sound and the battery is maybe 4 feet from me, but some people might notice it.

I been using a cheap 4 dollar 30a bms on my 220ah lifepo4, it works for the most part but everytime it disconnects charging when on solar it cause voltage surges and will replace soon. Recently I ordered a chargery bms8t (86 dollars) I still havent recieved to test it out, but it is fully programmable and monitors temp, can trigger external relays, and also is a coulombmeter 100a (needed for lifepo4) and it even balances at 1.2 amps. That might be something to look at, you can find on ebay. This seems to do most of what you want in a bms.

I also use a deadman switch (overvoltage protection relay) , its another layer of protection in case the bms fails. Its a relay that will disconnect the solar panel if battery voltage goes above a setpoint. I recommend this to everyone who charges lithium, the overvoltage relay cost 6 dollars, the 30a automotive relay is another 4 dollars, very cheap insurance.

 

[CoyoteThistle]

If I had it to do again, I'd do what LeishaShannon suggests - no active balancing and keep the voltage out of the "knees" with good pack-level management/protection (you'll want to do that either way of course).

That said, check out www.electriccarpartscompany.com. They have several different cell-level balancer/monitor options now (I got one from them a few years ago for $130 that is sadly not sold direct to the public any longer). No experience with their new ones, but last I looked they had some no frills options. reasonable shipping cost on CALB cells too.

For your pack disconnect relay, consider the Blue Sea 9012 solenoid too.

Best of luck with it!

 

[luthj]

I spotted this open source DIY BMS on another forum. It uses a LTC6804 BMS chip, connected to a arduino uno. This chip supports monitoring, temp, and balance control. The uno handles the logic, external relays, etc. External balance boards would need to be rigged up for balance currents over about 100ma, but existing units may be an option. Soldering the small LTC chip would be a pain though.

The major advantages of this setup is that I have complete control of the behavior. So I can use the BMS to drive pack heaters, multiple relays/contactors, etc. Hopefully there is an easy to use bluetooth library with graphic front end that I can use to report cell vitals and status. The uno can also be configured to read a hall, or shunt type current sensor, in order to drop the pack out in a overcurrent situation.

Arduino BMS Shield - 12 Cell - Share Project - PCBWay

This is a Battery Management System (BMS) board designed as an Arduino Uno shield. The BMS can handle up to 12 sieries connected cell modules and is fully programmable for any battery chemistry. The A...

www.pcbway.com

BMS_LTC6804

caditz.us

Basically this is a standalone type, which is good, cause I don't want to ditch all my existing components, which have proven very reliable.

 

[Rando]

Why not something like this:

4S Lifepo4 Battery bluetooth BMS with 100A or 150Aconstant discharge current for 12V LFP battery pack - LLT POWER ELECTRONIC

1) Application:this smart BMS can work for 4S Lithium ion or Lifepo4 Battery ,client can choose based on your battery chemistry features 2) Current : constant current of this version BMS can be 100A or 150A 3) Dimension:315*120*10mm 4) Functions : has full sets of protection for Li ion or...

www.lithiumbatterypcb.com

Inexpensive, completely configurable and self contained system.

(thanks hour for pointing these out previously).

 

[luthj]

I need 200A capacity. Though one of those bms could be modified to handle more current.

 

[Rando]

What is the 200A for?

 

[dreadlocks]

presumably for his big inverter.. but if you need a 200A load, have you considered a 24v solution? often comes with a nice efficiency boost for the inverter and you can push same wattage out 100A.. stepping down from 24v to 12v is pretty efficient for your lighter loads.

 

[luthj]

I cook with electricity, and have a custom bed cooling AC unit.

24V would be ideal, but I don't want to replace all my expensive gear and rewire. Plus I really like 100A+ charge rates from my alternator.

 

[Coachgeo]

Has anyone considered or done a battery eject system..... as in mount your batteries on exterior outside wall.... or just under rear of camper box outside behind axle.... with a way to literally drop them if fire starts in the lipo's allowing you drive away from the batteries.

 

[luthj]

I would not use Lithium Polymer batteries in a vehicle (I don't know anyone who does). Other lithium ion chemistry are not best suited for house packs (Li-CO for example). Lithium Manganese, and Lithium Iron Phosphate are well suited for house packs. They have lower thermal coefficients and flammability. Even if punctured they do not generally catch fire.

Li-CO and Li-Po are very flammable, and these are generally what is used to make those "lithium burns" videos on the web.

 

[Coachgeo]

I cook with electricity, and have a custom bed cooling AC unit.

24V would be ideal, but I don't want to replace all my expensive gear and rewire. Plus I really like 100A+ charge rates from my alternator.

Confused.... what does the 100amp charge rate have to do with going 24v? if your reffering to having a 12v alternator; there are awesome battery charge equalizers that will use your 12v 100amp alternator to charge 12v batteries that make up a bank of 24v or 36v or..... (or equalize several banks of xvolt batteries wired to make up a 12v bank)