Lithium battery, TV battery and 7-way plug charging

[bickp]

Thanks, makes a lot of sense.

[mtbackpacker]

Ive been thinking about this problem as well with my upcoming lithium switch over... personally I am leaning towards isolating the 7-wire from the house batteries entirely and installing a small trailer brake/breakaway battery on the tongue. I would use the 7 wire power to charge that like most utility and cargo trailers on the road. Bonus for this setup is that it is cheap, safe, simplifies the wiring, and lets me pull my trailer to and from storage without hauling out the trailer batteries out there and getting it all hooked up.

Anyone have any insight on how safe/legal it is to put all the lithium BMS/switch gear, etc in the loop for a critical safety system like the break away switch? I suspect the regulations probably were not written with any thing complex in mind...

[uncle_bob]

Originally Posted by mtbackpacker

Ive been thinking about this problem as well with my upcoming lithium switch over... personally I am leaning towards isolating the 7-wire from the house batteries entirely and installing a small trailer brake/breakaway battery on the tongue. I would use the 7 wire power to charge that like most utility and cargo trailers on the road. Bonus for this setup is that it is cheap, safe, simplifies the wiring, and lets me pull my trailer to and from storage without hauling out the trailer batteries out there and getting it all hooked up.

Anyone have any insight on how safe/legal it is to put all the lithium BMS/switch gear, etc in the loop for a critical safety system like the break away switch? I suspect the regulations probably were not written with any thing complex in mind...

Hi

Just leave the batteries in the trailer and things are even easier ..... Yes it depends a bit on just what your storage situation is.

Bob

[pjshier]

I am swapping the boat anchor 6 volts for LiFePo units for the coming season. I have read with interest this and several other threads and many other sources and will locate the new batteries in the front compartment. 2 100ah batteries; and we use a Renogy 200w solar suitcase and Champion 3400 located in the truck bed for most power needs (including charging) depending - we boondock a lot.

So far, I am thinking I can achieve some - not optimal - charging of the LiFePos while underway in our 300+amp TV alternator-equipped TV, using a Victron 12 |12 18amp Isolated DC-DC Charger mounted in the AS - knowing I will have to tweak the profiles to see even a modest benefit using the TV 7-way connector and to protect the stock TV wiring. Adding a 712 monitor just because. Seems like a reasonable approach given the excellent control and monitoring via bluetooth.

Question: In my research, I read where a Charger and a Converter are materially different, yet it seems possible these terms are being used interchangeably in this thread and a few others. What am I missing?

Since I upgraded to a Boondocker power center a few years ago as step one in the journey toward more power and battery health, I'd hate to think I should have purchased a Converter at this stage. I realize I WILL need more sophisticated gear in a few years when we go to add rooftop solar.

Thanks for your thoughts...

[Wazbro]

Originally Posted by pjshier

Question: In my research, I read where a Charger and a Converter are materially different, yet it seems possible these terms are being used interchangeably in this thread and a few others. What am I missing?

Since I upgraded to a Boondocker power center a few years ago as step one in the journey toward more power and battery health, I'd hate to think I should have purchased a Converter at this stage. I realize I WILL need more sophisticated gear in a few years when we go to add rooftop solar.

Thanks for your thoughts...

Well a Charger and a Converter can be separate or combined. A charger is only designed to charge the batteries, a converter is designed to provide 12 volt power to appliances, lights, etc... and a converter/charger is designed to do both. The devices currently designed for RVs are all Converter/Chargers or Inverter/Converter/Chargers so most people just shorten it to say either Converter or Inverter/Charger.

Inverter portion if it provides 120V from batteries, also inverter can be entirely seperate.

Some would argue the ones Airstream was installing until recently were only converters that also kind of charged batteries.

I'm fairly certain your Boondocker power center is a converter/charger.

[pjshier]

Thanks. Yes - the Boondocker is a multi-level charger and a converter in one unit. It performed much better than the stock unit, and is compatible with LiFePo. We just arent plugged in most trips. It gets used mostly in the driveway. Since I don't need another Converter, and won't be able to use that function underway, looks like the DC/DC Charger (only) is not a poor choice.

[Air4ME]

Originally Posted by pjshier

So far, I am thinking I can achieve some - not optimal - charging of the LiFePos while underway in our 300+amp TV alternator-equipped TV, using a Victron 12 |12 18amp Isolated DC-DC Charger mounted in the AS - knowing I will have to tweak the profiles to see even a modest benefit using the TV 7-way connector and to protect the stock TV wiring. Adding a 712 monitor just because. Seems like a reasonable approach given the excellent control and monitoring via bluetooth.

.

How is the Dc-DC charger working for you? Are you getting any charge using the Victron? I am trying to find a way to charge our lithium batteries while towing through the 7 Pin without running an additional cable.

[uncle_bob]

Originally Posted by Air4ME

How is the Dc-DC charger working for you? Are you getting any charge using the Victron? I am trying to find a way to charge our lithium batteries while towing through the 7 Pin without running an additional cable.

Hi

The DC/DC does work and you can get a charge through it. How well a 18A version will work is *very* truck make / model / year dependent. The manufacturers apparently love to play with this and that related to supplying power to the 7 pin.

Bob

[Justinfinity]

1. Whether you get any charge current on your 7-way depends on your tow vehicle.

2. Whether there is a current draw from your RV on your TV batteries depends on how your TV manages the 7-way connector.

3. Don't assume you'll get any worthwhile charge current through your 7-way connector. The wire gauge is too small and the TV probably wasn't designed to charge a second/large external battery bank through the 7-way.

4. Don't assume that a DC-DC charger will help if you are connecting it via the 7-way. The DC-DC charger won't magically overcome the inherent limitations of the 7-way connector, both in terms of the wire gauge and the way the TV manages the connector.

5. You need to bring high current from your TV to your RV through a separated dedicated umbilical connector and wire capable of high current.

6. Depending on your choice of LiFePo batteries, and whether they have a good BMS, you may or may not need a DC-DC charger.

In my case, as I have explained in other posts:

A. I ran fused 2/0 gauge copper wire (pos and neg) from the engine bay in my TV (Ford F250 diesel with dual alternator/dual battery) to an Anderson 350 connector on the rear bumper. I have a relay on an upfitter switch in the TV that allows me to engage or disengage the connection from the TV to the RV, while driving.

B. The RV (AS Globetrotter 27 FBT) has a similar run of 2/0 umbilical to the batteries (LiFeBlue 2x200Ah). These batteries are not stored in the original battery box. The original battery box is now just storage.

C. There is a Victron Cyrix-Li-Ct between the batteries in the RV and the connector on the TV. This also has a monentary switch that would allow me to supply current from the RV to the TV if, for example, my start battery were dead and I needed to start the TV from the RV battery bank. This is a nice bonus (which I have not needed so far).

D. I did not need a DC-DC charger nor did I need any kind of external BMS because the LiFeBlue batteries have an internal BMS that is about the best I have seen (at least the time of the installation).

E. I have done over 10,000 miles on this setup as far south as Florida and as far north as Canada, in temperatures ranging from 100F to -20F and I am very happy with it.

F. And, yes, depending on the BMS, you can use LiFePo batteries in freezing temperatures, and you can even charge them if you have a good BMS and a heat source (my LiFeBlue batteries have internal heating pads).

Bottom line, don't try to charge your RV batteries through your TV 7-way connector and don't assume that a DC-DC charger is a panacea.

[uncle_bob]

Hi

Most of us are quite happy to simply keep up with the fridge and a few other minor loads while bumping down the road. Doing that for $60 makes a lot of sense. If the batteries also top up a bit, that's a bonus. As long as you don't go crazy with the DC/DC the wiring involved is quite adequate for the task.

Bob

[pjshier]

Originally Posted by Air4ME

How is the Dc-DC charger working for you? Are you getting any charge using the Victron? I am trying to find a way to charge our lithium batteries while towing through the 7 Pin without running an additional cable.

Still don't have the TV back from the body repair shop - soon they say; frame had to be replaced. But here is the result of the test I conducted right after the DC-DC installation. 13.6v at idle isn't the 14.6v that LiFePo crave, but it is something for a LiFePo bank that is hungry after a few days boondocking.

https://www.airforums.com/forums/f53...ml#post2486250

[qwertyd10n]

Originally Posted by Air4ME

How is the Dc-DC charger working for you? Are you getting any charge using the Victron? I am trying to find a way to charge our lithium batteries while towing through the 7 Pin without running an additional cable.

I installed the Renogy 20A DC-DC Charger along with lithium batteries before this season and although we haven't really "needed" it, I have been impressed with how much charge it is putting to the batteries (confirmed with a Victron BMW-712 Battery Monitor).

Our tow vehicle is a 2009 Porsche Cayenne Turbo S and at idle the DC-DC Charger seems to be putting out 12-13A to the batteries. I haven't been able to check it while actually towing, but the batteries have always been more charged after towing to or from our three weekend destinations so far this season (fairly short, <2 hour drives).

We've got a few longer journeys planned in July and August, so it'll be interesting to see how everything works on those.

[hovr]

Originally Posted by qwertyd10n

I installed the Renogy 20A DC-DC Charger along with lithium batteries before this season and although we haven't really "needed" it, I have been impressed with how much charge it is putting to the batteries (confirmed with a Victron BMW-712 Battery Monitor).

Our tow vehicle is a 2009 Porsche Cayenne Turbo S and at idle the DC-DC Charger seems to be putting out 12-13A to the batteries. I haven't been able to check it while actually towing, but the batteries have always been more charged after towing to or from our three weekend destinations so far this season (fairly short, <2 hour drives).

We've got a few longer journeys planned in July and August, so it'll be interesting to see how everything works on those.

Glad to hear you had success with the 20a dc-dc charger.
Do you charge through 7-way cable or run separate larger gauge wires? If former what size fuse do you have in Cayenne's fuse panel for that wire? My ML 350 has a 20A fuse and the Renogy 20A dc-dc charger trips it all the time. I had to set the charging voltage very low so the current it draws is lower.

Thanks

[uncle_bob]

Originally Posted by hovr

Glad to hear you had success with the 20a dc-dc charger.
Do you charge through 7-way cable or run separate larger gauge wires? If former what size fuse do you have in Cayenne's fuse panel for that wire? My ML 350 has a 20A fuse and the Renogy 20A dc-dc charger trips it all the time. I had to set the charging voltage very low so the current it draws is lower.

Thanks

Hi

The current rating on a DC/DC is normally on the *output* of the device. The TV fuse is on the *input* of the device.

If you have 10V at the input to the DC/DC due to wire drop and 14 V on the output, you will be pulling 20 x 14 =28A into your 20A DC/DC converter. If it is only 80% efficient, you may be up around 33 A.

Will all DC/DC deliver full rated current with 10V in? Who knows ... they will all pull more than the rated output current as input current. That's just how they work.

If the people who designed your vehicle think that 20A is the most that should ever go down that wire, don't second guess them. Drop back to an 8 or 10A DC/DC if you are using the 7 pin.

There are a lot of vehicles out there with 30A and a few with 40A fuses on the 7 pin. The connector its self is fine with 30 to 40A.

Bob

[rfequity1]

Ok, so help me understand this. If I am reading correctly from the above posts, I am wondering if I’m going to have a problem. I have a 2017 Toyota Tundra, and a 25 FC. I am installing 2 105AH LiPo batteries in the trailer. Are you all saying that it’s going to drain my Tundra battery? How will I know if I have a problem? How do I find this 7 pin charge wire if I want to disconnect it? Thanks for the help.

[uncle_bob]

Originally Posted by rfequity1

Ok, so help me understand this. If I am reading correctly from the above posts, I am wondering if I’m going to have a problem. I have a 2017 Toyota Tundra, and a 25 FC. I am installing 2 105AH LiPo batteries in the trailer. Are you all saying that it’s going to drain my Tundra battery? How will I know if I have a problem? How do I find this 7 pin charge wire if I want to disconnect it? Thanks for the help.

Hi

The *big* issue is that your Tundra will drain your *trailer* battery as you go down the road rather than charging it. That's true pretty much regardless of make / model / year.

Bob

[rfequity1]

Originally Posted by uncle_bob

Hi

The *big* issue is that your Tundra will drain your *trailer* battery as you go down the road rather than charging it. That's true pretty much regardless of make / model / year.

Bob

Ah, gotcha. I think I can live with that. Maybe after some reports I report back the results.

[uncle_bob]

Originally Posted by rfequity1

Ah, gotcha. I think I can live with that. Maybe after some reports I report back the results.

Hi

The result is that you might have about 10A running from the trailer battery to the TV while you are in motion. If that goes on for 6 or 8 hours, your trailer has 60 to 80AH less when you arrive than when you started out. If you have two 100AH lithiums, they are now around 1/3 to 1/2 empty.

If you are going to go cheap, simply pull the charge wire from the DC block in the trailer. That eliminates the drain problem. It also means you aren't charging while going down the road. To charge you *do* need the DC/DC.

Bob

[dmassey321]

In my trailer, I need to be about 3 years old (size wise) to get to the 12v panel. Can anyone identify which wire on the 7Way needs to be clipped to prevent the battery drain on the Lithium’s? With my solar panels, I am (most of the time) going to get some amount of charge to the battery bank while driving...just don’t want my tow vehicle to drain the battery bank.

At some point we will add the DC/DC part but it was not available during our install 3 weeks ago.

Thanks,
Dave

[pjshier]

your F250 should have a schematic in the owners manual to show you which fuse manages trailer battery charging; just pull that fuse.