Lithium Battery Upgrade

[charliem]

I've not been following this thread closely but I have been thinking about the Victron DC/DC charger. I have a 2013 Toyota Tacoma TV which may or may not have a "smart"alternator. It does seem to stay at 13.6V then the TV battery is charged, which limits the TT charging even when connected with HD jumper cables. My question is, given the TV has a relay to prevent total TV discharge, what is the problem with disabling the Victron low input sensor and just letting it run with whatever it sees? Let one piece of smart technology defeat another piece of "smart" technology.

[DavidM]

I don't think that there is a relay that prevents total TV battery discharge, at least while the TV engine is running. There is a relay that disconnects the Pin 4 circuit when the ignition is off but I don't think it has anything to do with the SOC of the TV's battery. That may be what you are thinking of.

So, here is another test suggestion (I am full of them, aren't I?): Draw down the TV battery to about 50% SOC. Then repeat the test that was just done. Hopefully the smart alternator will kick up the voltage to recharge the battery and at the same time provide a higher input voltage to the DC to DC charger.

If that works then you may be able to solve your problem by defeating the Victron's cut out.

David

[charliem]

David,
I was referring to the ignition operated relay to isolate TV and TT. My real question was about defeating the low input setting on the Victron. Seems like that setting would only be useful in the absence of electrical TV/TT isolation. I'm thinking of using the Victron only when set up at a campsite and with the TV running and connected to the Victron with heavy wire. I'm concerned that, even with heavy wiring, the TV alternator would limit the voltage seen at the Victron to something lower than the low input setting. What's the problem with disabling the low input setting?

[DavidM]

"What's the problem with disabling the low input setting?"

None at all as long as the TV's alternator can be made (well fooled probably) to put out more than 12.6 volts.

David

[RV Squirrel]

In response to David's earlier question about alternator voltage... Yes, the alternator voltage was 12.6V when I did my last test with the low voltage lockouts disabled.  It's possible that the part of the 3V drop is because the DC/DC charger is drawing extra current to compensate for the lower voltage of 12.6V... and that extra current means even more voltage drop!  My math suggests that in an ideal case with #10AWG, the current draw should have been 25.6A (instead of 29.7A), and the voltage at the DC/DC charger should have been 10.8V (instead of 9.6V).  It's like I'm seeing one and a half times the resistance that I expected to be seeing.  Even though the 7-way connector is new, it probably is adding some extra resistance, as well as the hitch's junction box, and other connectors. 

During my previous tests, I tried to "fool" the alternator into operating at a higher voltage by discharging the TV battery before running the tests.  However, that didn't seem to work.  Perhaps I didn't discharge it enough, but I'd be a bit leery about discharging my TV battery a lot in order to charge my trailer battery.  This might be good for a test, but I wouldn't want to do it regularly. 

In a pinch, I would like to think that CharlieM's solution might be workable in a campground setting, where I can monitor things via Bluetooth on my cellphone, and had extra fuses.  With the current wiring and connectors, I'd have to expect a current draw of nearly 30A, if the alternator voltage was 12.6V.  If there is another way to get the voltage above 12.6V without draining the TV battery, that might be even better.

I agree that it's tough to get lithium batteries to charge with an alternator voltage of 12.6V.  In retrospect, it would have been good to have a DC/DC charger that would allow one to control the output current, so that one wouldn't have the larger voltage drops.  Without this, the only option (it seems at the moment) is to put in heavier gauge lines and better connectors.  I may wait awhile to do this.  Until then, I'll be glad to get 6A (IF I can get it) and carry extra fuses.  In a pinch, I would hope that I could disable the low voltage lockouts as CharlieM suggests.  Is there a risk of harming the alternator if I do this, particularly if the engine was idling at a campsite?

[Merlin]

In response to David's earlier question about alternator voltage... Yes, the alternator voltage was 12.6V when I did my last test with the low voltage lockouts disabled.  It's possible that the part of the 3V drop is because the DC/DC charger is drawing extra current to compensate for the lower voltage of 12.6V... and that extra current means even more voltage drop!  My math suggests that in an ideal case with #10AWG, the current draw should have been 25.6A (instead of 29.7A), and the voltage at the DC/DC charger should have been 10.8V (instead of 9.6V).  It's like I'm seeing one and a half times the resistance that I expected to be seeing.  Even though the 7-way connector is new, it probably is adding some extra resistance, as well as the hitch's junction box, and other connectors. 

During my previous tests, I tried to "fool" the alternator into operating at a higher voltage by discharging the TV battery before running the tests.  However, that didn't seem to work.  Perhaps I didn't discharge it enough, but I'd be a bit leery about discharging my TV battery a lot in order to charge my trailer battery.  This might be good for a test, but I wouldn't want to do it regularly. 

In a pinch, I would like to think that CharlieM's solution might be workable in a campground setting, where I can monitor things via Bluetooth on my cellphone, and had extra fuses.  With the current wiring and connectors, I'd have to expect a current draw of nearly 30A, if the alternator voltage was 12.6V.  If there is another way to get the voltage above 12.6V without draining the TV battery, that might be even better.

I agree that it's tough to get lithium batteries to charge with an alternator voltage of 12.6V.  In retrospect, it would have been good to have a DC/DC charger that would allow one to control the output current, so that one wouldn't have the larger voltage drops.  Without this, the only option (it seems at the moment) is to put in heavier gauge lines and better connectors.  I may wait awhile to do this.  Until then, I'll be glad to get 6A (IF I can get it) and carry extra fuses.  In a pinch, I would hope that I could disable the low voltage lockouts as CharlieM suggests.  Is there a risk of harming the alternator if I do this, particularly if the engine was idling at a campsite?

I've been struggling to figure out why you seem to be a special case, since charging an auxiliary battery (either in a trailer or for other purposes) using the vehicle alternator going through a DC-DC converter is very common and successful in the overlanding world. I think it comes down to having too high an expectation of the existing wiring and the 7 pin connector system. Those I've known to be successful use much large gauge wire, at least to the back cargo area of the vehicle, and in the trailer if feasible. Separate, heavy connectors are used too. As we all know, this 12VDC stuff is painfully affected by wire gauge due to the amps and resistances involved. I think you're fine running things as they are now, but I bet someday you'll get some bigass wire and find a way to get it all the way from the alternator to the camper battery, through all the appropriate safety and alternator preservation systems. Thanks for the continued interesting posts on this and to David for following all this so closely. If we had such a thing, you two would get the Tech Posts of the Year Award (TPOTYA) 

[DavidM]

Thanks Merlin. As you know RV Squirrel and I are collaborating on an article which discusses the issues involved with doing this. I had no idea it would get so interesting (at least to us Geeks) with smart alternators involved.

RV Squirrel- When you have everything installed send me an overall pic and I will incorporate it into the article as well as some of the issues you are facing.

David

[Merlin]

Squirrel, I've started to collect examples of others who have used the same DC-DC converter you have and most are using a minimum of 4AWG wire all the way from the TV battery. I can't seem to insert diagrams from the Pages program into ACF, but as I get good ones, I'll send them to your email, which I have.

[RV Squirrel]

Merlin, thanks.  If folks are using 4AWG wire, then it's understandable why I am having problems using 10AWG!  I think that you are right... I'll end up upgrading to a beefier cable and connector, but probably not any time soon.  Until then, I'll probably use the voltage limits while driving (and expect low charging rates), and in a pinch disable the voltage limits if parked at a campsite.

David, I only have one more thing to do, and that is to finish the cable for the solar panels.  However, the installation in the trailer is essentially finished.  I've attached pictures of the Victron equipment.  Pictures for the racks used to hold the AC/DC converter and the batteries are in this thread.  Like an idiot, I failed to take a picture of the AC/DC converter after I installed it in the tray and then put everything back together... but I can get one if you like.

Here is a picture of the Victron components, as seen from the inside of the cabinet where we keep dog kibble.  The wiring is routed from the other side, where the deck-mounted AC/DC charger and DC distribution box is installed. 


As you may notice, the positive bus bar is exposed, so I made covers out of sheet PVC.  They are held in place by "knobs" that I tapped so that they could be screwed on. I also covered the aluminum tubing near the positive bus bar with Gorilla tape (to act a bit as an insulator).  This may not be the best thing, but its better than nothing!
.

This is what the equipment looks like from outside the cabinet. 



For the solar cable, I'm currently looking for 8AWG "jumper cord" to connect to the MC4 connectors on the solar panels, but I've not been able to find it.  So I'll probably settle for two separate 8AWG positive and negative cables like these.  I'll probably make a short 8AWG "Y" cable to allow me to connect the MC4 cables into the Anderson connector on the trailer. 

I'm debating whether it is better to have one pair of long cables (say 40' one-way), or multiple pairs of short cables (for example, three 20' cables).  Having multiple pairs would allow me to configure the cables in series or parallel.  This would give me the following configurations, assuming that the MC4 connectors had no loss (probably not a good assumption).  All of these cable configurations assume that the solar panels are configured in parallel.  The cable losses are determined using David's WireSizer program.
-    Three parallel 20' cables (one for each solar panel).  5.3A per cable, 20' one-way.  1.2% percent loss.
-    One 20' cable (for all three solar panels configured in parallel).  16A total, 20' one-way.  3.5% loss.
-    Two 20' cables (for all three solar panels configured in parallel).  16A total, 40' one-way.  7.0% loss.
-    Three 20' cables (for all three solar panels configured in parallel).  16A total.  60' one-way.  10.5% loss.

I'm assuming that any drop in voltage on the input side will ultimately translate to the same drop in current on the output side, given that the output voltage remains the same (either 14.4V or 13.6V).  And if the parallel solar panel configuration resulted in too great a loss, I could play around with the solar panels in serial.

[Merlin]

Really nice wiring job! It's fun to look at stuff done well. 

[RV Squirrel]

Thanks!  After looking at the picture, I noticed that the cable to the circuit breaker is hanging down a bit.  I pulled this down so that I could put the clamp ammeter around it.  It's a handy spot for measuring current, but I need to stuff it back and/or attach another cable clamp to keep it in place. 

Regarding the "one long solar cable" vs "multiple short solar cables"... I've found out that the contact resistance of an MC4 connection and a Anderson SB50 connection are both comparable to about half a foot of cable (plus or minus... the Anderson is actually a bit better than the MC4).  So I'm thinking that it may make sense to buy multiple short cables and attach them as needed, and have the flexibility to put them in parallel if my solar panels are in parallel.

[Pinstriper]

It would be interesting to know if you could downsize the cables by running higher voltage from end to end, and converting it at either end to 12v

[RV Squirrel]

I suppose that running at 24V could have been an option.  Presumably, when running at twice the voltage you would have half the current, and therefore half the voltage drop.  I could have put my two batteries in series to get 24V (Battleborn supports series configurations up to 48V).  I'm pretty sure that the Victron solar controller supports this.  However, the Progressive Dynamics AC/DC converter and the Victron DC/DC converter that I have do not support 24V.  Anyways, the biggest problem is with the connection to the TV's alternator... so I'd need some kind of converter near the alternator. 

I'm comfortable making changes to the trailer, but making changes to the truck is another matter.  I'll probably end up making some kind of change, but I'll need to do some research first.  I'll probably be bugging you folks with questions, but it may not be until next year.  Thanks for the thought though.

[RV Squirrel]

I ran into a slight issue when crimping connectors for the solar panels.  Most of the MC4 connectors are only good for #10... I was not able to find one for #8 AWG.  I was intent on using #8 AWG wire, so that I could place the solar panels further from the camper.  However, I discovered that the crimp tool that I used for #8 lugs (going between components) did not produce as good a crimp on the #8 MC4 connectors for the solar panels.  The metal in the MC4 connectors is a thinner than that in lugs, and the resultant connection was wiggly-jiggly (technical term... don't feel bad if you haven't heard it before).  I actually had to insert a piece of solid copper wire into the crimp tool to create more of an indent into the crimp when using my "lug" crimper.  This wire was only there to help with the crimp and was removed afterwards. 

The bad thing about MC4 connectors is that if you aren't quite happy with something, you can't disassemble it after you've installed the backshell.  My only option with the first "wiggly-jiggly" MC4 connector was to cut it off entirely and replace it with another one. 

MC4 connectors do tend to be a little safer than other connector types, because the metal surfaces are less exposed.  Disconnecting them can be a bit of a hassle... even if you do have a tool, because not all MC4 connectors are alike.  The tool works better for some MC4 manufacturers than others.

[DavidM]

I found the same thing when installing MC4 connectors to run cables from my solar panels to my controller- thin material that doesn't form a good crimp. So I soldered them. Not the best solution as soldered wires have a hard connection that with long term vibration, can break.

David