LiFePo4 Batteries

[bdosborn]

I got the cells packaged with the balancers mounted and wired. I added a mount for the golf cart battery handle I already had because it still weighs 50# or so. 50# LiFePO4=145 usable amp-hr versus 144# Lead Acid=90 usable amp-hr so I'm lighter with more capacity. I'm doing a load test now to see how many amp-hrs I really have.





The balancers seem to work well, the cells are always within 0.01V or less of each other, when charging or discharging. I'm convinced that an amp capacity balancer is a good idea as I watch the cell voltages during charge/discharge. Most BMS have milliamp balancing capacity and don't help much when charging at 45A. The cell monitor isn't real accurate (compared to my Fluke) but its good enough to show a high level view of what the cells are doing.



I added fuses right at the positive terminal for peace of mind since there is so much short circuit capacity. I ordered an Arduino Nano kit off Amazon for $27 and plan to build my own BMS to monitor cell voltages and temperature. I'm having to rewiring my PV chargers because I added a Victron low voltage disconnect and it can only handle current going in one direction (which they don't state on the product data anywhere).

Bruce

[John61CT]

The Iota is adjustable right?

Just tweak it until you see no cell goes over 3.5V or whatever your top is.

Don't hand balance low down, do it starting at say 3.4, be consistent.

Then set pack LVC so no cell drops below 3.2V.

Once you have all this setup, the BMS becomes redundant, can try different cheap ones if you like as another layer of protection, but not depending on them.

I'll be looking at this but I don't know how it will work with the charge controller. Does the charge controller adjust all the voltages down proportionally with the internal pot or will it still expect to see 14.6V overall=charged?

Sorry you lost me. What "charge controller"?

And what do you mean by "all the voltages"?

There is only one voltage, the whole point is that your selected setpoint does not get exceeded.

If you mean Iota's module, their stop-charge algorithm should be well documented, and ideally AHT can be reduced to a short a time as you want.

You need to measure amps and volts at the battery until you see things are within the spevs you want.


> Looking at a Victron battery Monitor as it has a high voltage disconnect relay as well as midpoint cell monitoring

Pretty sure only one or the other.

> The Iota charge profile is real close to the recommended: Standard Charge Method:C/3 Constant Current to 3.65V Limit, then Constant 3.65V Voltage with Current Taper to C/20

Is there a shunt measuring trailing amps acceptance at the bank?

That is much more aggressive than I would want for longevity.

[John61CT]

I'm convinced that an amp capacity balancer is a good idea as I watch the cell voltages during charge/discharge. Most BMS have milliamp balancing capacity and don't help much when charging at 45A.

Yes, better to just do occasional balancing as needed, BMSs are pretty useless for that.

Avoid the voltage shoulders for longevity, and a good pack may not need rebalancing for years.

[bdosborn]

Sorry you lost me. What "charge controller"?

The Iota battery charger has a LiFePO4 charge controller called an IQ4, similar to a progressive dynamics charge wizard.

And what do you mean by "all the voltages"?

There are 4 cell voltages and the overall battery voltage that I'm looking at.

There is only one voltage, the whole point is that your selected setpoint does not get exceeded.

See above, there are 5 different voltages that I care about.

If you mean Iota's module, their stop-charge algorithm should be well documented, and ideally AHT can be reduced to a short a time as you want.

You would think so but its not documented well , and the charger doesn't behave like the data sheet that was included with the charger controller. There are no user adjustable set point either. I haven't found an adjustable charger for less than a grand.

You need to measure amps and volts at the battery until you see things are within the spevs you want.

Yup.

> Looking at a Victron battery Monitor as it has a high voltage disconnect relay as well as midpoint cell monitoring

Pretty sure only one or the other.

It will do both according to their installation manual.

> The Iota charge profile is real close to the recommended: Standard Charge Method:C/3 Constant Current to 3.65V Limit, then Constant 3.65V Voltage with Current Taper to C/20

Is there a shunt measuring trailing amps acceptance at the bank?

Yup, Bogart Engineering Trimetric 2020RV

That is much more aggressive than I would want for longevity.

I think so too, that's why I'm looking at available options.

Bruce

[John61CT]

The Iota battery charger has a LiFePO4 charge controller called an IQ4, similar to a progressive dynamics charge wizard.

OK, I'd just call that a part of the charger, just one that can be swapped out.

It will only key off the bulk voltage, 4S averaged together. An adjustable HVC could easily open the Iota input when hitting your desired setpoint.

Is there a shunt measuring trailing amps acceptance at the bank?

> Yup, Bogart Engineering Trimetric 2020RV

I meant as part of the Iota, else it can't tell what's bank acceptance vs concurrent loads.

The Trimetric could trigger a relay though right?

___
A separate external HVC monitoring at the per-cell level would be needed to shut the charger down based on a cell going over your setpoint.

Very common functionality for a BMS.

[John61CT]

Apparently the midpoint monitor triggers an alarm only, not the relay function.

[bdosborn]

The Trimetric could trigger a relay though right?

___
A separate external HVC monitoring at the per-cell level would be needed to shut the charger down based on a cell going over your setpoint.

Very common functionality for a BMS.

You'd think so but I couldn't find anything in the trimetric manual. My arduino kit arrived yesterday, I'm going to start playing with a DIY BMS to trigger a Victron battery protector. I already found a 4 channel voltmeter on the web.

Bruce

[John61CT]

I'd build in extra redundancy if relying on DIY gear to protect an expensive bank.

Plus keep a close eye out myself manually acting as "human BMS" 8-)

[KennethW]

I am thinking about using this lifepo4 80ah battery.
https://www.aliexpress.com/item/BLS-12V ... st=ae803_5
and this solar charge controler as it has low temp shut off.
https://smile.amazon.com/gp/product/B07 ... _413098310
With 450 watt of solar panels 3-150 watt 3 parallel for 12 volt? or 3 in series for 36 volts?
Any thought would be welcome

[bdosborn]

It seems like it checks all the boxes: onboard BMS, parallel up to 4, LiFePO4. The charge rate is low at 0.5C but the discharge rate is 1C, so you can support about an 600W inverter that surges up to 1200W. I don't know what a Lin communication is, Bluetooth maybe? It has a 1 year warranty but don't kid yourself, you'll have a hard time getting them to honor it. The battery terminals are starter type, but you can work with that. It doesn't mention if the BMS balances the cells, you might ask them about that as you definitely want that. I think it looks tempting for the price but I bet you'll have a hard time getting any kind of support from them if there are problems. You definitely want a battery monitor so you can keep an eye on the discharge and voltage status, despite the Lin communication.

Bruce

[KennethW]

I went for it. I know there is no real warranty. Now i will be waiting for that slow ship for china to get here to see what a am getting. I maybe should have when with this one as it is spec out better.
https://www.aliexpress.com/item/12V-100 ... st=ae803_5

[bdosborn]

Let us know how it works out, I'd be interested to hear how you like it. I've never bought anything from aliexpress but maybe I need to start browsing there. Lots of cool stuff...

Bruce

[bdosborn]

BTW, I setup the Victron Venus software (free) on a Raspberry Pi to monitor the new Victron MPPT controller and the Victron Battery Monitor. I should get an email if the battery voltage goes high or low, midpoint voltage deviates by more than 2% and SOC goes lower than 20% or higher than 100%. I can also look at the battery monitor values on a web page anywhere I have internet access. I'm using two Victron Battery Protects in conjunction with the Battery Monitor relay control so that the load is disconnected at 12V and charging is disconnected at 14.7V. This Victron stuff is cool. Here's a screen shot of the Venus Monitor page:



You can see where disconnected the battery to fiddle with some of the wiring and where I ran a test discharge of 38amp-hr or so...

Bruce

[MtnDon]

Let us know how it works out, I'd be interested to hear how you like it. I've never bought anything from aliexpress but maybe I need to start browsing there. Lots of cool stuff...

Bruce

I have bought a lot of electronic parts, small stuff mostly, as well as flashlights, raspberry pi and accessories. Virtually all transactions have gone well with what I ordered arriving in great condition and working. There have been a couple of exceptions over a 6 year period. Delivery speed is mostly slow.

If someday the Chinese favored status that gets them the very low international mailing costs is restructured the shipping costs will negate any benefit of buying direct. The sellers all usually offer money back returns but USPS and other shipping from the US to China costs make that impractical. On a couple of shipments where the seller shipped the incorrect, but quite usable, lithium cells, we came to an agreement where they refunded a few dollars to me.

[friz]

Keep us posted. Currently my battery represents 10% of my campers empty weight for a usable 50ah.

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