Daly BMS gone crazy..Update Opinions

Is it safe just to let the BMS just shut it down when it's charging?..

Not really knowing much about the BMS yet other than watching Will test them for low temp cut off and quite a few not shutting down in his test..

If it is safe,that's an easy way to know when it's full..

A bms on the batteries is there to protect the cells as a last resort. The emergency brakes on a vehicle.

Is it wrong to use it a standard stop gap? Your batteries, your choice. How many times can the bms components (electronics) take it?

Get chargers or inverter/ chargers, SCC that stop short of the extremes voltages would be my choice, which is implemented with my setup.

jaycocreek wrote:
Is it safe just to let the BMS just shut it down when it's charging?..

Not really knowing much about the BMS yet other than watching Will test them for low temp cut off and quite a few not shutting down in his test..

If it is safe,that's an easy way to know when it's full..

Welcome to LFP’s...

First off, your battery was EXPENSIVE Right??.... So you need to invest in a SOC (State Of Charge) meter that is designed to accurately translate LiFePo4’s SOC...Your bluetooth may provide this (??)...(If not, check-out Victron’s BMV 712, or equivalent)...

Routinely charging to 100% SOC is not necessary except to occasionally allow for BMS cell-balancing...(restores the cells to near-equal values).

With a ‘capable SOC LFP meter’ readout, once the batt gets to 100% SOC, after a brief ‘hold period’ you’ll begin to see the BMS doing it’s work - a kinda ‘to-and-fro’ repeating dance where voltage drops off a bit while current rises a bit until after about 15-20 min current holds at zero and voltage remains fixed at say 14.x...This scenario is with no other power draws the battery.

Beyond this, it’s not beneficial to let the battery remain for an extended period on an active charging source, and during longer periods of non-use, it’s best to deplete the SOC and store at an approx. 50’ish % or so SOC.

For a drop-in, this is about ALL the ‘expert’ you’ll ever need to be...

3 tons

You need an AH counting monitor to know ("well enough") your SOC when operating the LFP bank, because of the flat voltage curve. So you do need a way to zero that AH counter so it stays fairly accurate.

So even when operating while "avoiding the knees" as seems wise, you do still need to do a full recharge every so often to zero the monitor even though the battery may not need it as often. They do say to recharge to full every so often though and not for the monitor's sake.

It would be convenient if the two "every so oftens" occurred at the same intervals.

Knowing when the monitor is out of whack is another question with LFP. With FLA and AGM you compare AH count with (close to ) resting voltage and use the voltage/SOC table for your battery.

With LFP flat voltages how can you do that? What do you use as the cross-check? Itinerant1 mentioned something about his set-up being able to do that, not clear how, and how anybody without his elaborate set-up can do it.

Hi all,

Here is a summary from the article that BFl13 linked to:

"To sum up, for long and happy LFP battery life, in order of importance, you should be mindful of the following:

1. Keep the battery temperature under 45 C (113 f) (under 30C (86 f) if possible) – This is by far the most important!!

2. Keep charge and discharge currents under 0.5C (0.2C preferred)

3. Keep battery temperature above 0 C (32 f) when discharging if possible – This, and everything below, is nowhere near as important as the first two

4. Do not cycle below 10% – 15% SOC unless you really need to

5. Do not float the battery at 100% SOC if possible

6. Do not charge to 100% SOC if you do not need it"

I want to run a large inverter. At 50% of it's capacity, if I follow the guide lines in #2 of 0.5 capacity I would need 4 LiFePo4. If I followed the 0.2 of capacity, then I'd need 9. For SiO2, I'd need 1.

Compare that to SiO2 which can do 2.43 of capacity without damage, and no bms to worry about. SiO2 wins hands down on temperature range too. It wins on price, as well, unless you "roll your own", then LiFePo4 is wonderful.

I'm sure lots of people do run their LiFePo4 at 1 C successfully.

Not sure that article is accepted by the LFP owners here, but it rings true to me FWIW. Doing research, you know not to just read one author on any subject. You have to read several and get a feel for what is most likely. Papers have a similar rule about needing more than one source before printing a story.

I am on about monitors and how to zero them here because the OP could use that before deciding on the rest of his set-up.

Since it is important to operate avoiding the lower knee especially, and you want to exploit the LFP's lower SOC operating range (that you paid for!) you need to know when you are getting down to that lower knee with some accuracy. That is what the AH counting monitor is for, but it needs to be zeroed to stay accurate enough to do that for you.

A separate issue is avoiding the upper knee if that is the plan, when you have solar. Seems like you will be going past the upper knee quite often with solar. You can set the solar Vabs under the dreaded 14.6v, but how can you turn it off if you get to the top mid-day? Different issue though.

Actually the OP doesn't need a monitor his Bluetooth will do it once they send an update. He just needs a charger that does 14.4v instead of 14.6v.

Bluetooth monitors are nice as long as they stay working but then it can be said about a hard wired one.

“ I'm sure lots of people do run their LiFePo4 at 1 C successfully.”

Yes, and even a good bit beyond for starting dreaded heavier inductive loads (specifically, like air conditioners), but which begs the question, in ‘Real-Ville’ what kinda typical RV application is it that might require something as high as 2.43 C ??...Though a notable attribute, try as I might, I can’t think of one...

3 tons

Jayco, Be advised I sent you a PM on a possible charger mod...

3 tons

Itinerant1 wrote:
Actually the OP doesn't need a monitor his Bluetooth will do it once they send an update. He just needs a charger that does 14.4v instead of 14.6v.

Bluetooth monitors are nice as long as they stay working but then it can be said about a hard wired one.

Don't BMS monitors use cell voltage for the SOC? If so, how can that be any use for operating range monitoring where you want an AH counter because of the flat voltage curve?