First Trial of Lithium Battery Upgrade

[electric]

Voltage profile in LFP batteries is very flat until sharp "knees" at both ends, so it's normal to be around 13.5V for most of the charge cycle until last few minutes when it rapidly rises to whatever your charger is supplying.
Charge current limit with your WMCO is likely affected by very long wire from power center to the battery, both positive and negative, possibly even some negative path thru steel chassis, depending on where GND studs are located along the path. This creates a voltage drop, which limits charge current.
Try to measure voltage at the PC terminals while charging and compare with voltage at batteries.

[16ACE27]

Originally Posted by Lamokadave

So I finally had a chance to dig in to this a bit.
The premise here is Im considering a swap out of the WMO 9855 converter non lithium to something that supports lithium.
With some amount of difficulty I was able to pull the current deck mount converter. Im hoping some of you can help me understand what Im looking at.
As stated earlier, the converter circuit in the power center is a 15 amp breaker
The converter actually plugs directly into the back of the power center and has a single 6 awg red and white wire leaving it. I expected 2 of each with one headed toward the batteries and another powering house 12v systems. The white is routed directly to a neutral buss and the red goes back into the power center. In the same place the red enters the PC, another red exits and heads toward a device with a small circuit board and what looks like a couple of fuses. The red leaves that and heads into a very busy distribution device. At least one bundle of wires appears to connect to something labelled Vega so Im assuming part of the firefly system I dont really see any larger qauge wires that might head toward the batteries. So at this point, I dont know how the batteries are being charged. I've had no luck trying to trace things underneath as bundles of wires disappear between the frame members and coach bottom

You have a converter/charger external to the power center (pic 1) as opposed to those that are integrated into the power center.

The third picture is of your latching relay controlled by your USE/STORE (battery disconnect) switch - that's the path to your house batteries.

The rate of charge of your batteries depends on the difference between the charging output voltage, the charged batteries' output voltage, and the internal resistance of the batteries themselves and the internal resistance of the charger itself.

[Lamokadave]

Originally Posted by electric

Voltage profile in LFP batteries is very flat until sharp "knees" at both ends, so it's normal to be around 13.5V for most of the charge cycle until last few minutes when it rapidly rises to whatever your charger is supplying.
Charge current limit with your WMCO is likely affected by very long wire from power center to the battery, both positive and negative, possibly even some negative path thru steel chassis, depending on where GND studs are located along the path. This creates a voltage drop, which limits charge current.
Try to measure voltage at the PC terminals while charging and compare with voltage at batteries.

So an observation I made today.
I need to run a test requested by Renogy, so I've been draining the batteries a bit with 8-10 amp drain today. Once I got them down to under 80% I briefly turned on the PC just to make another observation of current and voltage into the batteries. 13.3v showing on the solar controller and renogy BT app, and approx 33 amps reported by the app. I used my DMM and measured ea of the 3 batteries at 13.4 volts. At the same time, the firefly system was showing 14.3v.
I believe the PC connects to a component of the firefly system all within inches of ea other so possibly very close to the PC the converter is outputting 14.3 or more volts and maybe there is voltage drop. The flat charging profile likely explains why my solar charge controller typically shows 13.3 - 13.5 and never shows 14.6v as I've never been almost completely charged relying on solar to complete the cycle.
The observation that concerns me is the new lithium converter charger brings the batteries to 99.1% but not higher, and never increases in voltage.

[Lamokadave]

Originally Posted by 16ACE27

You have a converter/charger external to the power center (pic 1) as opposed to those that are integrated into the power center.

The third picture is of your latching relay controlled by your USE/STORE (battery disconnect) switch - that's the path to your house batteries.

The rate of charge of your batteries depends on the difference between the charging output voltage, the charged batteries' output voltage, and the internal resistance of the batteries themselves and the internal resistance of the charger itself.

Thanks for explaining that 3rd photo. I've been unsuccessful trying to trace the wiring from the PC into the batteries. Between multiple wire looms joining together, and disappearing above frame members, etc, I've not been able to put my fingers on the wire charging the batteries at the batteries. At the battery positive I have a wire running to the BIM. One connected through a 300amp fuse that I believe is going to the inverter and one that appears to head toward the generator. I was assuming the feed from the PC would connect directly to the battery positive but I can't seem to identify it

[Lamokadave]

Did a little more work on this today and made some interesting observations. I started by pulling out the converter so I could measure it's output. It is putting out 14.53v. I then measured the input side of the battery disconnect relay and had 14.22 there. The output terminal of the relay measured 14.06.The firefly system was showing 14.5 and the solar charge controller was at 13.6.
So why am I losing voltage as it passes through the PC and the disconnect relay?
It's likely safe to assume that the rest of the loses are all due to transmission issues to the batteries be it wire gauge, connection points, ground lugs, etc.
I still need to find where the wire from the relay connects to the battery.

[electric]

You don't need to get to 14.6V, anything above 14.2V at the battery means it's essentially full. SOC interpretation on LFP is just that, interpretation, don't get hung up on it. Your converter at 14.5V is good enough, so you just need to either reduce V drop along the path, or simply accept your lower charge rate. If your MH is anything like my Vegas, it was clearly not designed to minimize voltage drop, they simply don't give a crap. When I install LFP batteries, I add all new cables from battery to charge source, straight 2/0 copper, both pos and neg, no chassis studs in the path. Even 1/0 should be enough in most cases, but not that OEM 6GA, it just won't cut it for higher currents at those distances.

[Bill Johnson]

Originally Posted by Lamokadave

Thanks for explaining that 3rd photo. I've been unsuccessful trying to trace the wiring from the PC into the batteries. Between multiple wire looms joining together, and disappearing above frame members, etc, I've not been able to put my fingers on the wire charging the batteries at the batteries. At the battery positive I have a wire running to the BIM. One connected through a 300amp fuse that I believe is going to the inverter and one that appears to head toward the generator. I was assuming the feed from the PC would connect directly to the battery positive but I can't seem to identify it

The 3rd photo, isn't that an early 1960s Ford starter solenoid

[16ACE27]

Originally Posted by Bill Johnson

The 3rd photo, isn't that an early 1960s Ford starter solenoid

No, see below

Originally Posted by 16ACE27

You have a converter/charger external to the power center (pic 1) as opposed to those that are integrated into the power center.


The third picture is of your latching relay controlled by your USE/STORE (battery disconnect) switch - that's the path to your house batteries.

The rate of charge of your batteries depends on the difference between the charging output voltage, the charged batteries' output voltage, and the internal resistance of the batteries themselves and the internal resistance of the charger itself.

[Bill Johnson]

They look almost identical, I'm sure they're different

[Lamokadave]

Originally Posted by Lamokadave

Did a little more work on this today and made some interesting observations. I started by pulling out the converter so I could measure it's output. It is putting out 14.53v. I then measured the input side of the battery disconnect relay and had 14.22 there. The output terminal of the relay measured 14.06.The firefly system was showing 14.5 and the solar charge controller was at 13.6.
So why am I losing voltage as it passes through the PC and the disconnect relay?
It's likely safe to assume that the rest of the loses are all due to transmission issues to the batteries be it wire gauge, connection points, ground lugs, etc.
I still need to find where the wire from the relay connects to the battery.

I continue to appreciate the discussion and help on this topic.
But no one commented on the voltage decrease in and out of the power center, and than again the latching relay that I measured. Is it considered normal? I guess I expected a near 0 lose through those components and only needed to deal with wire loses

[electric]

Originally Posted by Lamokadave

I continue to appreciate the discussion and help on this topic.
But no one commented on the voltage decrease in and out of the power center, and than again the latching relay that I measured. Is it considered normal? I guess I expected a near 0 lose through those components and only needed to deal with wire loses

I assume these measurements were done at max charge current, which you previously mentioned to be around 30A ?
0.16V loss across a solenoid at 30A is higher than I would expect, but these are not known for their high quality, so maybe somewhat normal, I don't have a lot of experience with cheap solenoids. The rest of your losses make perfect sense based on typical RV wiring. LFP battery has extremely low internal resistance, so anything close to the battery will be pulled down below 14V until the battery is full. You either have to bring charge source closer to battery or reduce transmission losses by rewiring and replacing components.

[Lamokadave]

Any danger in my running a separate line directly from the charger to the battery through a disconnect? I'd typically leave it in the disconnect mode but for those times I need to spike voltage for the final 1% charge I could flip the switch. That eliminates the PC and relay as degradation points and reallyh simplifies a remedy.

[electric]

Originally Posted by Lamokadave

Any danger in my running a separate line directly from the charger to the battery through a disconnect? I'd typically leave it in the disconnect mode but for those times I need to spike voltage for the final 1% charge I could flip the switch. That eliminates the PC and relay as degradation points and reallyh simplifies a remedy.

Why add another switch when you can simply replace the one you already have with a better one? Why only add a positive wire when half of your losses are on the negative side?
Your don't need a voltage spike for final 1%, you need more amps all the time to charge faster, unless I misunderstand what you reported earlier. If you only get 30A from a 60A charger, then you need more amps all the time, not sometimes.

If you have ability to run new wires, run both pos and neg from battery to PC, using at least 4 AWG. Here Amazon offers nice 25ft bundle for $80.
This will eliminate all chassis ground losses and most transmission losses.
New positive wire can be terminated at the relay, same as the old one, basically adding 2 wires in parallel. Remaining positive run from relay to PC is short enough, but you could also upgrade it to 4 AWG if possible. Replace disconnect relay with a good continuous duty contactor like Altran or Gigavac or even Trombetta, but pay attention to part numbers as many common Trombetta models are intermittent duty and you need continuous duty.

https://www.amazon.com/dp/B013DJKOLE...YNXRV3G36NPP17

[Lamokadave]

Originally Posted by electric

Why add another switch when you can simply replace the one you already have with a better one? Why only add a positive wire when half of your losses are on the negative side?
Your don't need a voltage spike for final 1%, you need more amps all the time to charge faster, unless I misunderstand what you reported earlier. If you only get 30A from a 60A charger, then you need more amps all the time, not sometimes.

If you have ability to run new wires, run both pos and neg from battery to PC, using at least 4 AWG. Here Amazon offers nice 25ft bundle for $80.
This will eliminate all chassis ground losses and most transmission losses.
New positive wire can be terminated at the relay, same as the old one, basically adding 2 wires in parallel. Remaining positive run from relay to PC is short enough, but you could also upgrade it to 4 AWG if possible. Replace disconnect relay with a good continuous duty contactor like Altran or Gigavac or even Trombetta, but pay attention to part numbers as many common Trombetta models are intermittent duty and you need continuous duty.

https://www.amazon.com/dp/B013DJKOLE...YNXRV3G36NPP17

The current wiring has the convertor negative going directly to a negative bus and only the positive into the power center. Only the positive goes to and away from the disconnect device. I was going to increase negative wire size to the bus from the second converter output and use a larger gauge from converter to switch to battery. I though by eliminating the path through the PC then through the current disconnect ( both which measured voltage loses), I'd both improve my current situation from all perspectives.

[electric]

Your plan for loss mitigation on positive side is understood, but comes at a cost of another switch, which is both monetary and usability cost, i.e. having to remember yet another thing to do when going to storage mode, etc. Sure, it can be done like this, but then why not replace the original switch instead?

Then you refer to negative connection as "the bus", as if it's not big part of overall losses, but its very likely a big contributor, unless you can trace or measure it and confirm how it compares to positive side losses. Main problem with negative is that RV makers use steel chassis to carry return currents, which is terrible for high currents as steel is a bad conductor.
So, my advise is that if you already decided to run a positive wire from the battery, then run the negative also, straight into converter, especially if it has unused 2nd terminal.