LiFePO4 Install

[john61ct]

set to 14.6 volts is a good setting
…
Lifepo4 will take every amp your solar panel can produce, up till the BMS shuts it off.

This is crazy IMO.

The BMS is there to act as a fail-safe in case your normal regulation / protective systems fail.

At both the high and low ends, by the time BMS isolates, if happening regularly you are throwing away for sure hundreds of lifetime cycles, potentially thousands.

Nothing wrong with "fast charging" but increase amps while keeping volts well under 13.9V.

> I have a .5 voltage drop in the system

You should fix that.

> Once the resting voltage goes below 12.9 volts you battery is almost dead.
Not true. 11.9V is still above 10%, especially if it hits that under a high load, let it rest it will recover.

Of course better to start recharging, and for longevity best to stay at higher SoC but no need to stress if you touch 12V sometimes.

> I lost about 4x 12 volt fans and many 12 volt lights from these surges, but havent since I added the relay.

Need a little cheap lead batt in line to buffer the load dump, same as alt charging.

 

[john61ct]

never want the BMS to disconnect from the controller. When that happens (isolates) the controller will try to force the battery to take a charge, this creates voltage surges which will destroy anything connected to the battery

This makes no sense. If controller disconnects from battery, how does anything connected to the battery (what should be very stable voltage) recieve voltage surges?

When the only battery is suddenly isolated, alt diodes, SCs, consumer electronics can often get fried.

Need cheap lead in the circuit to keep buffering the dump.

 

[luthj]

Higher quality chargers will have minimal voltage spike in disconnect, but it's still a risk. Ideally the disconnect is the last failsafe, a properly configured source is best. I put a cheap regulator on my alt (Bosch clone). When disconnecting a 150A load suddenly, the voltage spikes to 16v for a tenth of a second. That is with the starting battery in the circuit. Imagine how high it could go without a battery to absorb the spike? Thankfully a 5ah small engine starter battery in the circuit can safely suppress spikes.

 

[Wyuna]

How are you going to store your milk bottles now that you have the battery and all the other electrical gear in there

 

[dreadlocks]

I'm sure I'll find room somewhere in the dozen other milk crates, I kinda have a collection of em by now

 

[john61ct]

When the only battery is suddenly isolated, alt diodes, SCs, consumer electronics can often get fried.

Ok, but in the prior scenario, those devices are not connected to battery afterall.

The damage occurs from

A. the high-amp charge source, to

B. sensitive electronics

caused by spikes / surges, aka load dump, abrupt transition from Full Load to No Load, when

C. the only battery

is suddenly removed from that circuit.


The best known scenario is isolating a battery when the alternator is putting out high amps.

Also why wind gennies need to redirect output to a dump once their power isn't needed.

Not really sure how else to explain it.

 

[john61ct]

No actually same effect less power but can be similar results suddenly isolating the charge source from the circuit.

Best is stop the charging upstream, panels from SC, open AC circuit etc

 

[dreadlocks]

Got back sand dunes, made it home with 55% left in the tank.. only ran the generator for about 20mins in total to make some mac and cheese in microwave and coffee each morning.. If I'd of had solar on this I coulda done that off battery, the sun was abundant.

In less than hour of being plugged in at home its already at 80%, I'll shut it off here and leave it til next weekend when we take it back out again.. only seeing about 30A out of PD so I'm replacing the 10awg cabling I had with some 6awg cabling I salvaged out of another project.. that should let it dump the full 45A into the battery.

Bluetooth is really nice, with a baby sleeping in camper I could feed my curiosity from the fire ring.

*edit* so what you guys are trying to warn me of is dont pull the master disconnect while charger or solar is dumping a alot of amps into the battery or it might fry some of my DC components when the majority of the load vanishes and the voltage spikes? Could a cap help absorb some of that if it became an issue? I could just switch em off before pulling the master disconnect and it should avoid such mishaps.

 

[dreadlocks]

Been running my new Engel MT-80 on a test run this week, full of pre-chilled water bottles, fully charged I pulled the shore power at ~4pm Sunday.. today I got off work and expected it to had hit the LVD.. but alas this thing is still running


Its a bit weird getting to 40% capacity, and still having >20% charge left.. I'm wiring up the BMS to the LVD next but wanted to see when the LVD would shut off on its own..

Weather this week was pretty typical of our camping outings, a few hot days I left trailer closed up so it got ~100F inside, and few cooler days where it was cold at night and mid 70's in the day.. I ran lights a little bit every evening and the fan for a while when I was out there working.. I've been grabbing drinks out here and there and opening it a few times a day.. conservative for a typical trip but im just setting a baseline for light use with no input so if I am out hiking for a week I know my food is still good and I have cold beer waiting for me even if sun was not shining. One of the major abuses to my previous power system was those side excursions away from base camp, would come back and find battery in a critical state because I didnt have the capacity for that.

I upped the charger cabling to 6awg, and will time how long it takes to fully recharge off shore/generator power once this thing taps out..

*edit* added follow up shot 6h later to show voltage/soc

 

[john61ct]

What is the Engel LVD setpoint?

Is it adjustable?

 

[dreadlocks]

Engel has no LVD AFIK (if it does its like 10.5v or something useless), I would be referring to the Victron which the highest it will do is 12v by its self.. however I can wire the Victron Battery Protect (BP) up to the Battery Monitor (BMV) Relay output and set the Voltage and State of Charge cut off to whatever value I desire.. which will be ~12.7V/20% SOC, leaving me a reserve capacity if I get desperate but avoid reducing lifespan in normal day to day usage..

 

[dreadlocks]

So this morning the battery cut off at 12v had happened, system was safely shutdown @ 2-5% SOC.. thats pretty reasonable for backup reserve limit.


I plugged the charger back in around noon, took approx 4h to recharge



So with this test run done, I wired up the COM/NC Relay outputs on the BMV to the BP Switch, I'll wire up a simple switch in parallel with the BMV to act as a over-ride to access the remaining 15-18% reserve capacity..

 

[dreadlocks]

so this weekend I decided to rewire some of this, a while back I wired up a parallel over-ride switch with the Battery Monitor I can connect the LVD manually and did alot more research on LiPo's this is the plan.

I moved the charger over to the load side of the battery protect and bonded internal 12v circuits back up to the charger output in the breaker box.. I then started using the dual battery feature of the battery monitor and wired up the starter battery monitor up to the load side of the battery protect.. Now the Battery monitor see's the voltage on both sides of the battery protect.

I set the "High Starter Voltage Relay" to 14.4v and the "High Voltage Relay" to 14.2v.. What I'm hoping this will do is disconnect the charger when the battery reaches 14.2v, then keep it disconnected while we are on shore power because the starter battery will be 14.6v (>14.4v).. everything will be powered by the AC power supply, then when I disconnect shore power the battery will be at resting voltage (<14.2) and it will reconnect.

If the battery gets into a low SOC state and the Battery Protect/LVD disconnects, I can use the manual over-ride switch momentarily to reconnect em when the charger is powered..

When I get a Victron Solar controller I'll wire it up in parallel with this circuit, so it will shut down when on shore power.

*edit*
Diagram:

 

[shade]

Any changes since the above?

If starting from scratch, would you do anything different?

 

[dreadlocks]

oh yeah thats changed quite a bit.. would I do anything different? not really, thats why I did it this way.. I might had bought a more expensive Victron LFP, but not sold entirely on if that woulda been worth the extra premium ontop of the BB premium.