Home assemble LiFePo4

[xsilvergs]

I had a look at a few of his videos this afternoon, but unsure about his conclusions about cell balancing.

I guess it confirms that not all BMS work the same.

I would love to build my own BMS considering some of the thought provoking things he covers. I bought a couple of Ecotree 110ah batteries, time and the thought of giving my money to China was more stress than my ticker could handle.

 

[SquirrellCook]

Based on bits I’ve managed to retain, I think the cells I’ve purchased are “raw” cells with a capacity measured in a way similar to lead acid. So 280ah is really 200 and a bit in real useable terms. This is staying above 3 volts per cell and not charging much above 3.4 volt, avoiding a absorption stage. So in a retail package this could be marketed as a 200ah battery that can be run to 0% charge without harm. The electronic management taking care of what the customer experiences. Take this another step further, you don’t even need high performing cells. As long as their actual capacity exceeds the claimed capacity.
For a conclusion at this stage the cells I have purchased will exceed four T105’s at a reduced rate. This still being about 1.5 times the capacity of the lead acids. The other feature not often mentioned is a more stable voltage range.

 

[wildebus]

I think your 280Ah cells are actually either 280Ah or very close to it usability to 100% DoD. 200 and a bit would be a very conservative discharge.

Example of a commercial packaged battery bank in my van.... 2 x 100Ah (nominal) LiFePO4 ....

Taken 212h out the 200AH bank - full discharge but the battery cells, although nominally and sold to manufacturer as 100Ah cells test to around 108Ah.
If I were building a bank out of those batteries I would for sure do a full discharge test on all the cells to confirm capacity

 

[SquirrellCook]

Three jobs are required then David.
1. I need to connect mains to the multiplus in Betty.
2. Make a lash up with the BMS and lifepo4’s
3. Use Betty to discharge them and recharge.

I’ll have to check my stock, but I think a Victron smart shunt will be on my next order David.
A small fan heater should make a good load.

 

[wildebus]

Three jobs are required then David.
1. I need to connect mains to the multiplus in Betty.
2. Make a lash up with the BMS and lifepo4’s
3. Use Betty to discharge them and recharge.

I’ll have to check my stock, but I think a Victron smart shunt will be on my next order David.
A small fan heater should make a good load.

If you are doing the testing in Betty, I would suggest a BMV rather than a Smart Shunt. The 700 is a very similar price, when connected to the Cerbo you can use VE.Connect on it just like the Smartshunt, but as well as a screen you gain access to a programmable relay which could come in useful at some time.

 

[Derekoak]

When you get to adding the heaters I think an extra temperature cut off at say 30 C Is a good idea. I just think that other controls in the front line can go wrong. I would hate the heaters to just to on heating. I am going to add such a thing.

 

[wildebus]

When you get to adding the heaters I think an extra temperature cut off at say 30 C Is a good idea. I just think that other controls in the front line can go wrong. I would hate the heaters to just to on heating. I am going to add such a thing.

I would cut off a lot earlier than 30C.
If you use a temp controller to switch on the heaters below a set temp (say 5C?), it will go off above that temp anyway so that would take care of the situation anyway without extra sensing needed.
You mention about a 5 degree hysteresis on your controller? On many you can adjust that to whatever you want. Pretty sure you can on the one I posted a link to a little while ago (and which is the same I think as the one shown in the video below?)

I remember watching this chaps video on his lithium install and incorporating heating pads. might be of interest (I find his videos well presented and the quality of his work excellent. Wouldn't go far wrong emulating him)

 

[SquirrellCook]

It’s a well known fact that paranoia goes hand in hand with a good engineer. I forgot about the little Chinese temperature controlled relay. I have one on my desk. Two of them in series failing open would be good. For good measure a bimetallic switch could be added to.

A good idea about the BMV, it could be placed nearby the Battery. I was thinking about the Cerbo or Multiplus for a relay, but I think one of them has a job already. It’s tough when you don’t know what you are doing.

 

[SquirrellCook]

I would cut off a lot earlier than 30C.
If you use a temp controller to switch on the heaters below a set temp (say 5C?), it will go off above that temp anyway so that would take care of the situation anyway without extra sensing needed.
You mention about a 5 degree hysteresis on your controller? On many you can adjust that to whatever you want. Pretty sure you can on the one I posted a link to a little while ago (and which is the same I think as the one shown in the video below?)

I remember watching this chaps video on his lithium install and incorporating heating pads. might be of interest (I find his videos well presented and the quality of his work excellent. Wouldn't go far wrong emulating him)

Just suffered the video
Please DON’T use a cut of disc indoors, the mess will make you regret it later.
And the cack handed way he used the hacksaw made me cringe.
I would’t use an aluminium frame for batteries in a domestic installation, if something went wrong the consequences could be frightening.
As for the blue LED’s I was brought up to be boring.

 

[Nabsim]

All the battery thermostats I have for Votronic and Victron equipment say to mount them on the negative battery pole, (may have just said battery pole and I used negative).
Not had my 700 out for a while but from my admittedly poor memory I seem to think you can either connect to VE or connect a BlueTooth dongle (not built in this model). If you aren’t wanting BT in future then a good saving to be had
And I did a specific video on the Daly BMS being okay but I don’t remember it’s title. The balancing just worked differently to how he thought it would but it did work once he had it figured out.

 

[wildebus]

I don't know if it makes any difference, but it does seem to always be "secure to -ve pole", yes.
When I wanted a couple more monitors in my van, I got the BMV-700s and happy I did rather than SmartShunts.

Differences:
Smartshunt - Built-in Bluetooth.
BMV-700 - Need to add Dongle to use Bluetooth.
If you are a Venus OS (Cerbo/Venus/etc) user, then you can connect to either device using VE.Connect via VRM and bluetooth becomes unncessary. I find I connect to all the Bluetooth-enabled devices as well as the BMV-700s using the VRM method as more convenient.

Smartshunt - 2 inputs
BMV-700 - 1 input
So you can monitor either a second Voltage, or a temperature with the Smartshunt. The voltage bit could be handy, but the temp option if you have a Cerbo is less important (it has 4 temp inputs anyway). There is a BMV-702 that has two inputs.

Smartshunt - no relay
BMV-700 - relay
The programmable relay on the BMVs can be very useful. not that many people seem to use the feature, but they should.

Smartshunt - no head display
BMV-700 - physical display
It can be handy to have a display you can glance at without having to use your phone. In my own case, I have a BMV-712 with display visible, but the two BMV-700s are tucked away and the displays are not that important, however I can get info on them via the screen connected to the Cerbo.

Generally speaking, for a Primary standalone Monitor, I would go for the BMV-712 (full features so use in every way) first, followed by the Smartshunt.
The BMVs are awkward to configure and setup via the head display, so you want to be able to use VE.Connect (either by Bluetooth or VRM)
For a Venus OS system with connectivity, I wouldn't bother with the SmartShunt, but go BMV-700 or BMV-712 if you want a second input (the cost of the 702 is not far off the 712, and the 712 has bluetooth and a better relay anyway).

Remember you cannot have both a Bluetooth Dongle AND a VE.Direct cable connected, so if you are not sure if you will use Bluetooth or VE.Direct in the end, you would be best off with a device that has built-in BT so you keep your options open, which means a BMV-712 or Smartshunt

 

[Derekoak]

You mention about a 5 degree hysteresis on your controller? On many you can adjust that to whatever you want. Pretty sure you can on the one I posted a link to a little while ago (and which is the same I think as the one shown in the video below?)

I looked at the temperature parameters. On my daly smart 100. I cannot see a hysteresis control. The only temp settings I do not understand are diff temp protect set at 255C at the moment and MOS temp protect set at 0C.

 

[wildebus]

I looked at the temperature parameters. On my daly smart 100. I cannot see a hysteresis control. The only temp settings I do not understand are diff temp protect set at 255C at the moment and MOS temp protect set at 0C.

They will be component temp monitoring I guess? though 255C is extreme and maybe a default that needs setting?

 

[Derekoak]

They are defaults, but I do not know what to set them to. I guess MOS is as in mosfet but I do not understand. Oh well things are working at the moment.

 

[SquirrellCook]

I thought I'd order a couple of little bits of wire to connect the cells to the Multiplus. 2 x 50mm2 tinned copper wire 5 metres long. I nearly fell of my seat at the prices.

 

[wildebus]

oh yes. prices have 'edged up a little'

 

[SquirrellCook]

Test firing today, yes they take a charge.
Box fabrication soon.

 

[SquirrellCook]

Heat pads turned up today, I might have a go at box making tomorrow.
Battery wires connected to the electrical box ready for lots of sultanas.

A couple of old batteries for now to aid playing.

 

[Derekoak]

I have successfully heated my battery from cold until the bms were satisfied and charging began. I know now that my pads take 12 amps whilst heating. My bms will be set to 5C but they have a lag so must be heated to 10C to loose the low temp fault setting. My cells under my heating regime are about 1 degree C cooler on the none heated side compared to the top of the heated side. So it is best to site the bms thermistors ontop of the heat pads. My heat pads are between each pair of 100ah cells.
It took 9 minutes to heat the cells from 6C to 10C using about 2Ah of battery. If the ambient was just 5C it would take about 11 minutes to get to charging temp. If the ambient was 0C it would take 22 minutes.
I have set the w1209 temp switch to a backlash of 6.5 degree, with a temperature to switch off the relay of 12C. That means that it will instigate charging at 5.5C to ensure it is set before the bms go to fault at 5C. When I switch the ignition on charging will begin and switch off at 12C by which time the bms sensors will be at 10C and ready to charge. Then I can start the engine to recharge immediately. Only the first relay coil will drain the starter battery, all other load is from the leisure battery. I will gain back the 2Ah of heating loss from the batteries in just over 2 minutes of running the engine.
I can still use my ring solar controller for solar, but it cannot charge or heat the batteries when it is cold. I will see how often there is enough solar charging opportunity lost before I try to deal with that.

 

[wildebus]

I think you are right to see just how much you could loose from solar before finding a 'solution'. I suspect it will be tiny.