Lithium Charging voltage low in Bulk mode

stepheng · March 2023

I have a 2022 320S BD with the WFCO 8735LiS power center. I recently purchased a 100Ah Powerurus LiFePo4 battery. The charging voltage from the WFCO (switch set to Lithium) should be about 14.8V when in bulk mode, but it is only about 13.7V - 13.8V. I also tried charging with the Victron solar controller only and its output was 13.7V - 13.8V at the battery as well. I disconnected the battery and measured the voltage from the WFCO as 14.8V with the solar charger turned off. I then pulled the fuse on the solar wire connected to the battery (and turned the Victron charger on) and it measured 14.8V. It appears the battery is clamping the voltage. Has anyone observed this?

I tried calling WFCO tech support today, but they never returned my call.

The battery is failing as it can only deliver about 4 amps for a few hours before the battery voltage goes to zero.

I have contacted the manufacturer and they have asked me to fully charge (but I need to do this at 14.8V) and then let them know the battery voltage after an hour of rest. I have ordered an external Lithium charger that should be here tomorrow and will try to charge with that and see if it can be charged at 14.8 volts.

I'm leaving for the Terlinga Rally Monday so I'll have to go to plan B and put my old LA battery back in for the trip and deal with this when I return.

Any thoughts?

techietab · March 2023

This is a known headache with WFCO power centers: https://tab-rv.vanillacommunity.com/discussion/16210/wfco-wf-8735-ad-lifepo4-fyi-on-annoying-auto-detect-quirk

Marceline · March 2023

Did you change the settings on your solar controller for this new battery? Even if the WFCO doesn't properly charge it, the solar controller ought to.

techietab · March 2023

2nd'ing Marceline's comment. You need to use the Victron app to change the settings on the MPPT controller to boost the voltage for Lithium batteries.

techietab · March 2023

It actually appears I misinterpreted which WFCO model you have. With the Switched model like you have (as opposed to the auto-switch model discussed in the thread above), you may be running into voltage drop due to the wire gauge and distance between the power center and your battery. The stock 12v wiring between the power center and the battery is smaller than ideal guage in the 2022 320S.

stepheng · March 2023

I did change the Victron charge controller to the correct voltages for Lithium. The output voltage is correct if the battery is disconnected. The wire from the Victron charge controller is 10 Gauge and will deliver 14.5 volts to the battery at 10A assuming 15 feet of wire. So when I had the solar only connected to the battery, the voltage was 13.7 or so. When I cycled the Victron Charge Controller off and on I did observe that the voltage was about 14.5 volts for a second or two then dropped to 13.7. Know why it would do this? Shouldn't it keep the voltage at 14.5 volts for some period of time?

You may be right about the voltage drop from the WFCO as that would be more significant at 25-30 Amps.

SLJ · March 2023

I have the older WFCO and decided not to replace it for charging lithiums. I'm installing a Victron AC charger right next to the batteries to be used just for charging the lithium batteries when on shore power. Much better quality charger. The WFCO will be reduced to just be supplying AC and DC power when we're plugged into shore power and I'll have the batteries switched off and charging with this Victron https://amzn.to/3LbDfaF

stepheng · March 2023

@SLJ Did you add an external relay that connects the battery to the Victron charger and disconnects it from the WFCO automatically when you connec to shore power? I have thought about doing that.

Here's what I was thinking:

SLJ · March 2023

stepheng said:

@SLJ Did you add an external relay that connects the battery to the Victron charger and disconnects it from the WFCO automatically when you connec to shore power?

No, I added a second disconnect switch just for the batteries when I moved them inside and will just switch them out when I plug into shore power and switch them back on when shore power is disconnected. The Victron will only charge them when shore power is on. It can stay connected to the batteries even if AC is off. The roof solar and my external panels will charge them when shore power is disconnected.

Denny16 · March 2023

You can also connect the solar charger directly to the battery bank using a 30 amp fuse, so,the sola charge the battery bank regardless of AC being on or off.
If you have the solar/controller disconnected when on shore power, be sure,to turn solar charging off on the Victron phone app, instead of a physical added switch.
Cheers.

stepheng · April 2023

Update - When I returned from Terlingua I determined the Powerurus battery was not working properly - probably a bad BMS, but I returned for a refund. I did confirm the voltage drop issue is the wiring from the converter to the battery in the tub being 10 AWG. I considered pulling 6 AWG wire but it would not be easy after looking at the routing under shower and the exit under the trailer near the junction box with my inspection camera.

I have the Victron SmartShunt installed and here is what I have decided to do:

Image: https://us.v-cdn.net/5021717/uploads/editor/03/to9pjthf5650.jpg

The Victron Blue Smart charger, the SmartShunt and the MPPT solar charge controller will be connected using the ve.network feature.

When connected to shore power the relay will disconnect the WFCO and connect the battery to the Victron Charger. The Victron charger will detect the voltage at the battery and compensate for the wiring voltage drop by increasing the output voltage of the charger so that the voltage at the battery is correct. This is much simpler than re-wiring. I have also confirmed that this approach should work with tech support at BattleBorn.

This leads me to one other thought - why not just remove the converter from the WFCO and replace it with a good 12V switching regulated power supply that will fit in the cabinet. This will provide good DC power when on shore power and voltage compensated charging for Lithium batteries with minimal wiring changes.

Thoughts??

SLJ · April 2023

stepheng said:

Update - When I returned from Terlingua I determined the Powerurus battery was not working properly - probably a bad BMS, but I returned for a refund. I did confirm the voltage drop issue is the wiring from the converter to the battery in the tub being 10 AWG. I considered pulling 6 AWG wire but it would not be easy after looking at the routing under shower and the exit under the trailer near the junction box with my inspection camera.
This leads me to one other thought - why not just remove the converter from the WFCO and replace it with a good 12V switching regulated power supply that will fit in the cabinet. This will provide good DC power when on shore power and voltage compensated charging for Lithium batteries with minimal wiring changes.
Thoughts??

I ran 8 gauge wires from the tub to inside leaving the original battery junctions in the tub (now in a weatherproof box). Did that two seasons ago. Found that to be pretty easy going under the floor down the passenger side from the front. With the Lithiums I just installed I did wind up just putting in a manual switch right at the batteries. A relay is an interesting idea but I'd want an override or bypass. Pretty easy for me to just flip a switch when on shore power and let the new Victron smart charger charge them if needed. Also gives me the option of leaving them on and having the Victron and/or the WFCO capable of charging them. The Victron can also be put in DC power supply mode as a backup if the WFCO ever craps out. This is what I wound up with:

Image: https://us.v-cdn.net/5021717/uploads/editor/vb/248r76q2zo5e.jpg

Image: https://us.v-cdn.net/5021717/uploads/editor/bl/f0eus0829ij8.jpg

Each battery is on it's own 50A breaker/switch. The new Victron smart charger is in the compartment with the Air8 with it's own switched AC outlet and a 30A breaker/ switch.

The Renogy battery monitor with it's shunt seems to be working great. I can just flip one thing on and read what it's drawing from the batteries. Decided I'd rather have the Renogy on the wall without having to depend on my phone. Fits nice under the Air8 control panel. The Victron smart charger, battery monitor, and solar controller are all talking to each other and my phone.

Image: https://us.v-cdn.net/5021717/uploads/editor/f7/rivae69dna1u.jpg

stepheng · April 2023

So I made the modification in my post above (except the DC-DC converter) to test with my Lead Acid battery before purchasing the Lithium battery. My WFCO power converter had a full size 20A breaker for circuit 5 so I replaced it with a dual 15/20A breaker and used the new 15A circuit for the Victron Blue Smart charger and the AC power to the SPDT relay (amazon - https://a.co/d/a8oCiC6). By simply turning off the 15A breaker the converter will work as wired prior to the modification.

When I first connected the trailer to shore power, I verified the relay was connecting the Blue Smart charger to the battery and the trailer's DC circuits were being supplied DC power by the converter. I did not initially enable ve.networking and measured the voltage at the battery as 13.6 volts with both a voltmeter and the SmartShunt. The Blue Smart charger showed an output voltage of 14.2 volts in the Victron app, thus confirming the voltage drop of the 10 AWG wiring. Current was about 16A. I then enabled ve.networking and the app showed the Blue Smart charger increased the output voltage to 15.07 volts, 17.2 A and 14.35 volts at the battery. I confirmed this with the voltmeter on the battery as well.

This means you can upgrade to Lithium, leave the battery in the tub and use the existing 10 AWG power wiring as the Blue Smart charger will compensate for the voltage drop. Now I need to order my Lithium battery.

Below are a few pictures of the installation and screen shots from the Victron app.

KK1L · April 2023

@stepheng I have been thinking of putting in a Victron Blue Smart charger as well. I guess I am not fully understanding something though. In your scenario you have a relay to switch out the WFCO and switch in the Blue Smart when AC is applied. However the WFCO would not supply 12V unless on shore power, so there is never a situation where it is active and in line. What am I missing? Why not just drop the relay entirely? I must be missing something.

@SLJ I follow your approach of switching the AC to the Blue Smart with a unique switch on the WFCO converter output. I think I like the combination of your approach with @stepheng where the relay to switch the WCFO 12V out of the circuit is controlled by the AC supplied to the Blue Smart.

Image: https://us.v-cdn.net/5021717/uploads/editor/nj/pzqcfwzb16wm.png

KK1L · April 2023

I love good tech and having a consistent system, but am wondering if the extra spending is really necessary and am second guessing my want to add the Blue Smart charger. For a lead-acid system I would say it is. For LiFePO4 not so sure. Please check my thinking below.

@stepheng You determined that the original issue was a battery problem and not due to the charger.
Bulk charge mode is current based. Voltage is adjusted by the charger to keep a constant current. For LiFePO the voltage at the battery terminal is not important, since they can handle even 1C charge current.
When current drops then the charger switches to constant voltage mode. With a lower current the error between the charger and the battery is less. The error reduces to nearly zero as the current drops. Again not an issue as it is current flow which charges the battery.
In float mode the error is nearly zero since nearly no current is flowing.
While in float the charger is providing power to the camper 12V. Voltage at the battery should be at the charger output voltage since there is no current flow to/from the battery.

stepheng · April 2023

@KK1L When you are connected to shore power 110VAC is applied to the relay (and the Blue Smart Charger as its plugged into the new 110VAC outlet I installed) and switches the "battery" wire to the Blue Smart charger output so that it supplies the charging voltage to the battery. The converter will then only supply 12VDC to the fused DC circuits connected to the converter. When there is no shore power the relay connects the WFCO to the battery which then supplies 12VDC to the fused DC circuits in the trailer.

KK1L · April 2023

@stepheng Ah ha! I knew I was missing something. That makes sense. I was assuming you were intercepting the output of the WFCO. I get it now!! Thanks.

stepheng · April 2023

Bad battery was an issue, but everything I read said you needed to charge lithium batteries at 14.2 - 14.4 volts (constant voltage) to balance the cells. You just can't do that with the WFCO and 10AWG to the battery.

I considered the same thing - as the battery charges, the current supplied by the charger will decrease and the voltage at the battery will increase thus reducing the effect of the voltage drop due to the wire resistance. I could never get an answer if this was an acceptable way to charge the battery.

The Blue Smart charger is a much better charger (and appears to provide a higher charging current than the WFCO when on shore power) and the ve.networking solves the voltage drop issue and keeps a constant voltage at the battery when charging. I figure for about $150 it was a good investment.

KK1L · April 2023

@stepheng I don't need much convincing to up the tech

Regarding the extra $...we don't call our camper "Running up a T@B" for nothing

2nd solar charge controller $120
smart shunt $120
DC-DC isolated charger $170
EMS HW30C $140 (good deal)
Suitcase solar panel $160
various Schmidt to hook it all up (other than what I had around) $50

The proposal is to relay in the AC-DC charger (I have relays) at about $205. Is it better than the WFCO? Arguably yes from an integration standpoint (VE.connect to the shunt and another ). Will it provide more current? I watched the WFCO source nearly 50A at the shunt for for the several minutes I was watching having turned it on after the battery had discharged down a ways. So the 55A WFCO is going to beat the Victron in this case.

I have updated the schematic that has been floating around in the forum (I would give direct credit, but forget who originally generated it) to show the add-ons (thick black border) and the proposed add-on (thick red border).

Image: https://us.v-cdn.net/5021717/uploads/editor/uu/jqiq0zozlcl9.png

stepheng · April 2023

Looks like you have a 400. Mine is a 320 and only 35A WFCO (8735Li) - after internal DC loads I don't get that much charge current when on shore power. My motivation was to avoid moving battery and/or replacing wiring with 6 AWG to solve voltage drop issue. I already had SmartShunt so adding charger, relay, new breaker and outlet was about a wash with rewiring.

Yoshi_TAB · September 2023

Hi @stepheng

Looking at this thread because I also want to hardwire an external charger for my lithium batteries. I like the idea of a relay to automaically do the switch. A few questions to make sure I'm clear.

1. I know you added a new outlet to plug the charger into. Your drawing shows AC wires to the coil side of the relay. Where or how did you get the AC wires for the coil side of the relay? Did they also tie into the new breaker you installed for the charger power?

2.Which pos. DC wire from the WFCO is tied into NC side of the relay (#6 30A)? From the middle picture, it looks like it goes into a small positive bus bar, but not in the dwg...but not sure.

3. Does the DC neg from the new charger need to be tied into the WFCO as shown in dwg or can it go to a neg bus bar (looks like it from the picture)?

4. The circle object after the 30A fuse in your drawing... is that a pos. busbar shown in the middle picture?

5. Did you disconnect the OEM charger in the WFCO?

My current set up has the charger portion of the WFCO wired into a transfer switch (I also have an inverter) so it's only powered when on shore power. The WFCO charger (for LA batteries) never goes into charge mode when on shore power with my lithium batteries. My theory is (I'm not totally sure on this), the lithium batteries never drops below the voltage that is normally needed for lead acid. In other words, even when a lithium battery is say at 30-40% SOC, the voltage is still higher than a fully charged lead acid battery and the charger algorithm never starts the charging process,

Thank you

AnOldUR · September 2023

You guys (gals) are killing me. Been perfectly happy using a NOCO and a cigarette lighter port tied directly to the batteries. Now I see adding a dedicated charger and relay in my future. The wiring diagrams in this thread will be a huge help. Thanks!

SLJ · September 2023

I added a Victron Smart Charger instead of updating my WFCO controller. No relay needed. I put a master kill switch on the batteries and put the Victron charger on a switched AC outlet. When on shore power I shut the batteries off and flip on the Victron charger. When I disconnect shore power I switch the batteries back on and turn off the charger. Easy and avoids the hassle of upgrading the WFCO and adding a relay which could be another failure point down the road. If the WFCO ever fails the Victron Smart Charger can supply the DC to everything as a back up.

otr_320 · September 2023

OP appears to be experiencing a 5% voltage drop at 17a while charging. Quite a bit. Most installers will strive for less than 2%. A 5% drop at low current levels is mostly a performance issue. At higher current levels it becomes both a safety and performance issue.

We sometimes charge at 100-110a for hours at a time. Even though we're only experiencing a .8% voltage drop, our short run of 2/0 welding cable still gets warm to the touch.

stepheng · October 2023

@Yoshi_TAB sorry for the late reply. Here are the answers to your questions.

1. yes, I pulled power off of the new outlet and ran two wires over to the new relay AC coil so that it is energized when the trailer is plugged into shore power.

2. The positive output of the WFCO is connected to the NC terminal of the relay. The common terminal of the relay is connected the wire coming from the battery shut off switch. The NO
terminal is connected to the positive (+) output of the blue, smart charger.

3. The minus (-) terminal of the blue smart charger is tied to negative bus bar with all the white wires.

4. The circle in the drawing is the battery shut off switch in the tub in the front of the trailer.

5. I did not disconnect the charger in the WFCO. It still supplies the DC power to the trailer when plugged into shore power. I only eliminated it for charging. The relay reconnects the battery to the DC circuits in the trailer when you are disconnected from shore power.

AnOldUR · January 9

SLJ said:

I added a Victron Smart Charger ...

About to take this project on. My NOCO Genius10 works fine, but it can be slow and that is one of the reasons for this upgrade. It looks like you went with the 20A Victron charger. Beside the $30 difference, is there a reason to not go with the 30A version?

To keep it simple, I'm planning to mount the charger in the front tub with our two 100 amp hour LiFePO4's and a short run of 6AGW. My plan is to plug it directly into a small propane generator for the rare case when solar has not been keeping up. Running the generator for 1/3 of the time of the NOCO is the goal.

https://www.amazon.com/gp/product/B08NY23BKF/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&th=1

Yoshi_TAB · January 10

Hi @AnOldUR

I have the30A version. I am far from an expert, but I do follow a few RV electrical forums. From what I've read from others, there is no reason not to go to the higher amp if your wiring matches the charger amp rating. No cons, but the advantage of getting a faster charge of your batteries. I have read there is a maximum , but its way up there (I forgot the formula). I believe the new TAB 320s with the lithium package come with the Victron 2000W Inverter/charger that has the 80 amp charger version( from a grainy picture).

SLJ · January 12

AnOldUR said:

SLJ said:

I added a Victron Smart Charger ...

About to take this project on. My NOCO Genius10 works fine, but it can be slow and that is one of the reasons for this upgrade. It looks like you went with the 20A Victron charger. Beside the $30 difference, is there a reason to not go with the 30A version?

I went with the 20A to keep my budget total cost for the Lithium upgrade including the the two 100AH batteries under $1,200. When I plug in I have plenty of time for the batteries to charge at 20A and if I ever have to use the charger to supply DC to the whole camper (doubtful), 20A will be plenty to run everything 12 volt I use. If I ever find I need more (which I doubt) I can just add a second smart charger and they will both operate together. I have solar and my tow vehicle charging the batteries and have seldom used the charger. When I do it's just for topping off, typically when in the garage when I return from a trip or just before I leave on one.

AnOldUR · January 13

Not as nice or clean of an install as many of you have done, but it works.
I know. Spaghetti wiring mess.

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Lithium Charging voltage low in Bulk mode

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