Lithium Battery Upgrade

[RV Squirrel]

Before I made any more "permanent" changes, I was hoping to see how the DC/DC converter performed if I bypassed the 7-pin connector and the #10 AWG cables entirely.  I ran #8 AWG red and black cables under the trailer (just laying on the driveway) and connected it to the input of the DC/DC converter.  I used a jumper cable to connect the other end to my truck battery, and reran the tests that I did a couple of days ago.  Since I bypassed the 7-pin connector, I didn't take readings at the junction box. 

Appliances plus lithium batteries (12.55V TV voltage):
Current into DC/DC charger: 26.9A
Current out of DC/DC charger: See note below
Voltage at TV battery: 12.55V
Voltage into DC/DC charger: 11.1V
Voltage out of DC/DC charger: 13.5V

The good news is that, for the test that included the batteries, the current into the DC/DC converter was reduced by almost 4A.  It's still high though.  I wasn't able to measure to current out, because as I was about to do so I noticed a change in the voltage and current.  This was probably because the alternator started charging as a higher voltage.  So I recorded these new values as well.

Appliances plus lithium batteries (13.87V TV voltage):
Current into DC/DC charger: 23.0A
Current out of DC/DC charger: 19.0A
Voltage at TV battery: 13.87V
Voltage into DC/DC charger: 12.7V
Voltage out of DC/DC charger: 13.6V

Since the TV voltage went up, the current draw dropped from 26.9A to 23.0A. I wonder why the alternator decided to provide a higher voltage output today, but didn't do so a couple of days ago.  I've since read that the alternator will reduce voltage in order to avoid overcharging the TV battery, or if there are heavy current draws, but I'm not sure how that would play into what I'm seeing here.

I bypassed three things in the test that I did above... the wiring between the alternator and the 7-pin connector in my TV, the 7-pin connector itself, and the wiring from the 7-pin connector to the DC/DC converter in the trailer.  As Merlin suggests, I will replace the 7-pin connector, and see how much of a difference that makes.

The link that Merlin has above is for an "RV style" connector.  I assume that "RV style" refers to pinout and wire colors, as suggested here.  I plan to get a 6' cable, because that is the length of my current cable.  Anyone have an opinion on which is better... Bargman or Hopkins?

[RV Squirrel]

I went to etrailer.com, and noticed that the Hopkins 8' cable was comparable in price to the Bargman 6' cable.  However, the Bargman seemed to be a little better due to the double-bladed "pinch" connectors (assuming that this makes a difference) and silicone cable, so I ordered that.  I made sure to get the "RV style" connector.

[keeena]

I recently got the Bargman 8' when rewiring my HD tilt trailer this spring. You can argue whether it its worth $75, but it is a very nice pigtail; super flexible and high quality wire. You won't be disappointed.

[RV Squirrel]

I recently discovered how NOT to clean the 7-way connector on the back of your tow vehicle.  Yesterday, I tried to do this using steel wool.  The moment I tried to do this, the 12V got shorted to ground through the steel wool.  It started to glow a very pretty color.  Good thing that I did not have any volatile solvent on it... otherwise I'd be writing this post from the intensive care unit.

I installed the Bargman 7-way connector today.  I'm happy to report that it was not as exciting as yesterday.  I was surprised, however, to see that insulation for the cable as well as the individual wires were all silicone.  This did make the cable pretty flexible as Keeena had noted.  The light blue color of the cable does clash a little with my "blue granite" Silverado, but I'm willing to make that sacrifice if the silicon protects the cable better.  I hope that I'll never be camping if -67F temperatures, but if I am, I'll be glad to note that the insulation is rated for use at that temperature!

I also cleaned the connectors using CRC QD Electronic Cleaner and then applied CRC Dielectric Grease just as it began to rain.

After installing the 7-way connector, I repeated the test that I did a couple of days ago.  Since it was raining pretty hard by now, I did not go out to measure the voltage at the truck battery.  I think that it was probably around 12.6V.  I'm wishing now that I had verified this.

Appliances plus lithium batteries:
Current into DC/DC charger: 25.2A
Current out of DC/DC charger: 19.2A
Voltage into DC/DC charger: 11.8V  (a drop of .8V from assumed truck battery voltage of 12.6V)
Voltage out of DC/DC charger: 13.6V

The current into the DC/DC charger was around 1.7A less than the test that I did a couple of days ago, when I bypassed the old 7-pin connector using a jumper cable and #8AWG cable.  The voltage drop was smaller too, 0.8V instead of 1.5V.  Current and voltage out of the DC/DC charger was about the same. 

The current into the DC/DC charger was around 5.6A less than the test that I did last week, when I was using the old 7-pin connector.  The voltage drop at that time as 2.74V!

So, as Merlin suggested, the new connector really helped.  Thanks Merlin!  Thanks also to David for his insight.

I still wish that the current as a little lower though... 25.2A is still cutting it close to 30A. And this is with the output voltage being 13.6V, not the 14.2V that might occur once the batteries are discharged significantly.

I still have the #8AWG cable hooked up underneath the trailer.  Sometime I may run another test using #8AWG cable for the trailer, instead of the #10AWG cable that is hardwired right now.  I may also re-run David's voltage drop test and see what values I get at the junction box for the 7-way connector... this might suggest how much of the loss is occurring through the length of the truck and the connector.

[Merlin]

Thanks for the cleaning tip! I suppose that also might apply to wire brushes that could lose a bristle in the wrong place.

Good work on the V/A testing and results. I suspect (but don't know) that you'll be ok with the 25.2A current on a 30A fused circuit, even if the voltage rises. Carry a spare!

[DavidM]

Good job! I think you have squeezed all you are going to get out of that Pin #4 circuit. I agree with Merlin that 25 amps is marginal for a 10 amp circuit on a 30 amp fuse. But I also think that as the batteries get more fully charged and the charging voltage from the DC to DC charger rises to 14+ volts, the battery's acceptance amperage will drop giving you more leeway.

As noted above keep a few 30A fuses on hand. If they do blow with some frequency then your only choice is to run a parallel circuit with the existing one to keep the amps down below 30. If you keep the original one active you don't need 8 gauge. 10 gauge will do fine with a 30A fuse so that both share the load and the amperage in each will be below 20A.

You might even try tying in the new circuit into the existing 30A fuse in parallel with the old. I suspect the lower voltage drop with a parallel circuit will result in a higher voltage into the DC to DC charger which should drop the current below 25.3A.

David

[RV Squirrel]

Remember when I said that I didn't measure the voltage at the truck battery because it was raining?  Well, I should have!  The next day I reran the test.  I thought that the TV battery voltage was 12.6V, but it was really 14.05V.  That means that if the TV battery voltage really did drop down to 12.6V, I could be consuming up to 4A more current.  I bypassed the 10AWG cable in the trailer with 8AWG and reran the tests, but the results were negligible.

I have a trip coming up at the end of the month, so I plan to use the existing cable in the tow vehicle.  However, I will plan to use the voltage lockout feature of the DC/DC converter to disable the charger if the input voltage drops below a certain point.  I'll also be sure to carry extra fuses.

FYI, I contacted Victron and asked if there was some way to limit the current output of the DC/DC charger.  They said "no".  I was hoping to keep the unit working with half of the current, rather than try to provide max current and then turn itself off because of a voltage drop!  Their recommendation was to bypass the OEM equipment in the TV with parallel cable, fuses, and connectors. My recommendation was that they include this little tidbit in their marketing material.

Sometime in the future I may try to add parallel cabling.  I was hoping to add additional (or thicker gauge) cabling after the 30A fuse in the TV, as David mentions above.  I looked under the hood of my 2014 Silverado, and noticed that there was not convenient access to 12V posts as there was in earlier model Silverados.  There isn't much room around the fuse box, and the cabling looks like it would take a lot of guesswork to figure out, and a lot of work to reassemble.  A lot of tape and loom!  Medusa would have approved, though.

I guess that I would add a parallel line before the fuse, with a fuse of its own... and maybe even a separate cable/connection to the trailer (via something like Anderson connectors).  This makes my head hurt a little bit though.  I wonder if I may somehow be undermining the function of the original fuse.  Is anyone aware of other threads where folks might have done something like this for other applications?

[DavidM]

The only problem with running a parallel line from a different spot on your TV is that it probably won't be switched by the ignition like the OEM circuit is. This is important to keep from running down your TV's battery.

David

[RV Squirrel]

Good point... although I think that pin-4 may always be energized on my Silverado anyway.  I didn't have the keys in the ignition when I managed to ignite the steel wool while cleaning the connector! 

In addition to the shutdown voltage that I mentioned above, the Victron DC/DC converter has a "startup" threshold that it uses to determine when the engine is on.  This may be helpful.  However, the voltages change so much when I connect the house batteries that it may be necessary to start the truck, then run into the trailer to switch in the house batteries, and then get back into the truck to start driving. This could be a problem if I had to do this every time I stopped for a break, but it beats having a dead battery.

[RV Squirrel]

Last Thursday I finished installing the Anderson connector on the underside of the trailer, so that I could easily plug in a long cable to the solar panels.  I was eager to get the Anderson connector installed, because that meant that I could finish all of the work on the trailer for the Lithium battery upgrade.  All of the connections inside the trailer for the Victron equipment were now complete, and I could put everything under my kitchen counter back together... including the cables that came from underneath the trailer into the AC/DC conversion area underneath the cooking range.

I managed to do this just in time so that I could take the trailer to a family reunion in the Alleghenies in PA.  The surroundings weren't too exciting... I was parked in an in-law's driveway... but it gave me a chance to check out the DC-DC converter and exercise the battery capacity.  Although we didn't spend much time in the camper, our aging dogs did, and we made sure that every fan was available to be put to use if it got too warm.  We refrained from connecting to 120V, and used the lithium batteries for normal functions as well as popping out the slide-outs, water pump for showers, and recharging our iPhones.

Since the batteries were fully charged before we left on the trip, I did not expect any charging to occur via the DC/DC charger.  However, I was hoping to connect to the DC/DC charger while we were on the road.  Unfortunately, I was not able to use Bluetooth to connect to the Victron DC/DC charger... I don't think that the signal could make its way out of the steel cab on the Silverado and into the aluminum trailer.  Therefore, I couldn't tell what was really going on with the DC/DC charger.  During the 43 hour period that we were parked, we consumed around 70AH.  This is around 1.6A per hour.  When we got back home after a 5 hour trip (including a .5 hour break to eat lunch), the available capacity had increased by 27AH.  This means that the DC/DC charger charged the batteries 6A per hour on average.  The nominal output of the charger is 18A per hour, but I suspect that there were times that the charger turned itself off due to under-voltages.  While the charger was actually charging, the current was probably much greater than 6A, but if it got too high then the voltage drop from the cabling might have been enough to turn the charger off.  I really wish that I could have connected via Bluetooth so that I could have seen what was going on.  At least I didn't blow the 30A fuse! 

For the solar connection to the trailer, I used Anderson connectors because they are easier to attach/detach that MC4 connectors, and should be able to carry more current than MC4 or SAE connectors (which seem to be available with thinner wire gauges, but not thicker ones).  The ones that I purchased can carry up to 50A.  I mounted the connector on the underside of the trailer using a Trailer Vision mount.  It has a spring-loaded cap that hopefully will keep some of the road crud from splashing onto the connectors.  I tried to put it someplace that would be easy to reach from the side of the trailer, but not someplace that would get excessive spray from the tow vehicle or the wheels of the trailer.  I've attached a picture.   I used 8AWG wire with protective loom, which was fed through the same opening on the underside of the trailer that was used for shore power and the 12V from the 7-way connector.  Since the Victron solar controller was in the same area, cable lengths were pretty short.

I still have MC4 breakout connectors and an MC4 fuse just before the solar panels.  I still need to make a cable that would have an Anderson connector on one end and MC4 connectors on one end, to connect to the solar panels.  Ideally, this would be a 30-40 foot UV resistant zip-cord cable at least 8AWG thick.  BatteryCablesUSA advertises 6AWG (no 8AWG), but it is currently out of stock and may not be UV resistant.  If anyone has any recommendations that aren't copper clad aluminum (CCA), I'd love to hear it.  A lot of stuff on Amazon is only 10AWG and/or CCA.

[DavidM]

Interesting that you only recharged your batteries at about 6 amps while driving home. That is about what I used to get without a DC to DC charger from pin 4 of the 7 pin connector.

Since you seem to like fiddling with this stuff (like me) how about setting up a static test for an hour or so. First run the batteries down to about half, then start the TV's engine with the TV hooked up to the trailer. Also if possible put something on the throttle to raise the rpms up to 1,000+ rpm so the alternator is fully powered.

Then watch all of the voltages/currents for a half hour to an hour to see what is really going on.

Have fun!!!

David

[RV Squirrel]

Actually, I was glad to get that much.  I really do think that the DC/DC charger is turning on and off, and your test would be a good way to confirm this.

In the past, I wasn't really able to rely on DC charging at all.  During one of the first trips out with the Camplite, I made the mistake of leaving the refrigerator on DC while we drove.  When we arrived at out destination, the house battery had gone down from 93AH down to 25AH!  The refrigerator had been consuming the battery power, and the tow vehicle was doing little (if anything) to replace it.  Since we were at a non-electric site, I had to use the tow-vehicle to recharge the battery without the refrigerator running.  Even that seemed spotty... probably because the truck alternator was switching between 14V and 12.6V.  I've read that the alternator will reduce voltage if it thinks that it may be overcharging the truck battery, but I'm not sure where the "logic" is to implement this.  I tried little tricks to keep the alternator running at 14V (turning on tow mode and turning on the high beams), but I'm not sure if this made a difference.

I read your post yesterday, and have since disconnected shore power.  Once the batteries get depleted halfway, I'll try the test that you suggest.  This may be a good time to try out the refrigerator on DC power, now that I've replaced the broken relay that kept it from working in the past.  That will be sure to consume a good amount of power from the batteries.  I've been reluctant to "waste" the energy, but this might kill two birds with one stone.

[DavidM]

When you do the test, keep an eye on the TV's battery voltage. Newish vehicles have "smart alternators" that do as you describe and cut the alternator output voltage under certain circumstances.

With the TV alternator voltage at 12.6 and a voltage drop of maybe a volt, yes the Victron may be shutting down and that would explain the low average amperage you noticed.

Something similar happened to me when I was trying to jump start a friend's car using our 2017 Mini as the charging source. The current through the battery cables would suddenly drop to near zero and wasn't doing anything to put a quick charge into my friend's battery. The Mini's alternator was cutting the voltage.

FWIW that car is too smart for its own good. You can't even change the battery yourself. As the battery ages the smart alternator compensates and if you replace the battery it stays the same unless you know how to reset it for a new battery by using an OBD2 device. I gave up and took it to my nearby independent shop and they reset it for me (or so they said).

Technology is getting too smart for us!

David

[RV Squirrel]

Last night I had left the refrigerator on in AC mode with four quarts of ice to to help bring down the temperature. This morning I ran the refrigerator on DC mode.  It consumed around 15A, but the new relay worked and I was confident that I could use my refrigerator in DC mode... even if it were to consume a lot of current.  Since it was hot, I also had the fans on... this added another 5A of current.  So the refrigerator and fans were consuming around 20A.  It took around 5 hours to get the lithium batteries to 100AH.  By early afternoon I was ready to start the test!

I turned on the ignition in the truck, and monitored the voltages and current.  The voltage into the Dc/DC charger was around 13.1V, and the output voltage was around 13.2V.  The output current varied a lot, but seemed to be around 6A.  This confirmed what I saw during my recent trip.  Even though the maximum current was 18A, the charger would turn itself off because once the current became too high, it would cause the voltage to drop below 13.1V (the default threshold for engine shutdown detection).  I thought that this cycle might occur every two or three minutes... but it was actually happening much faster than that.

Rather than wait to collect more data (like an adult would), I decided to stop the test and lower the threshold to a lower value to see if this would let me get more than 6A!  I got nothing.  By that time, the alternator decided to sit at 12.6V.  I turned on tow mode, high beams, and sat there with my foot on the gas pedal, but the alternator still sat at 12.6V.  At that voltage, the DC/DC converter declared that "engine shutdown" was detected, and kept the charger at a disabled state.  It seemed that the alternator reduced the output voltage to keep from overcharging the TV battery.

So...  I did my best to run down the truck battery.  With the 7-way connector connected and the engine off, I turned on my high beams, running lights, and even recharged my iphone from the cigarette lighter. 

After 45 minutes or so, I reran the test.  As soon as the truck started up, the TV voltage would be around 14V.  The DC/DC charger would produce around 10A at 13.3V.  A couple of minutes later, the TV voltage would drop to 13.1 volts,, and the DC/DC charger produced around 6A... but this would decrease to around 4A a minute later.  A minute after that, and the TV voltage would drop to 12.6V, which would ultimately turn the DC/DC charger off due to "engine shutdown detected".  I am now wondering how I got an average of 6A of recharging on my recent trip.

For grins, I disabled the "engine shutdown" and "low voltage" thresholds.  The DC/DC charger drew 29.7A.  The input voltage was 9.6V.  It provided 17.9A at 13.5V.  It didn't blow my fuse, but came pretty close!

[DavidM]

"For grins, I disabled the "engine shutdown" and "low voltage" thresholds.  The DC/DC charger drew 29.7A.  The input voltage was 9.6V.  It provided 17.9A at 13.5V.  It didn't blow my fuse, but came pretty close!"

Was the alternator voltage still at 12.6 while this was going on? If so that means a 3V voltage drop which is about double what you earlier reported. Could there be a new bad connection in the circuit.

If you could get the voltage drop back to a volt and a half or so, then the current would drop to about 25A. The other way is to run a separate larger gauge circuit, maybe even #6 gauge to keep the voltage drop down to a half a volt. That would probably drop the current even further, maybe into the low 20s even if the alternator is only putting out 12.6 volts.

But.... when the Li batteries get more charged they are going to want more voltage to maintain the 18 amps charging rate which will drive the alternator current back up.

But at the end of the day, it looks like you are fighting a losing battle with your smart alternator. An alternator voltage of 12.6 just isn't going to work well with a battery that requires as much as 14.4 V for a full charge.

David