How do I determine if DC-DC charger is necessary?

[Jack West]

I am taking delivery of a New Basecamp 20 next week. It will be fitted with two 100A Battleborn LiFePO4 batteries (and a Victron BMV712). I have a 180W solar suitcase I will use to keep the batteries topped up while camping and also Honda 1000W generator for additional juice if needed while camping. My TV ('06 Tacoma) has a 130 A alternator and I have charged my previous 3 trailers (all lead acid batteries) thru the 7pin on my Tacoma while towing. I have read and watched videos of folks with bigger lithium battery banks installing a DC-DC charger. I understand there are other threads where this is discussed, but I do not want to damage my TV battery or alternator while on my shakedown trip or towing the trailer 300 miles to its new home. I would appreciate any advice you can give me to avoid damage to either the AS batteries or the TV alternator/battery.

[dznf0g]

I would advise a DC-DC converter, with either AGM or Li-ion batts. Unless you want to run a larger cable all the way from underhood to your AS batts, I advise the 18 amp Victron model. That is, IF your truck has a 30amp, 10ga wire existing in the 7-way toyota trailer harness/connector. I think that 18A will do well for you in at least 90% of your camping/recharging scenarios. Solar and the gennie will take care of the rest.

[Steamy1]

I installed the Renogy 20a dc-dc charger and tapped into the 7-pin wiring from the TV.

It does charge my two (2) lithium LION batteries. A side benefit is that if the TV power wire in not energized, it cuts out so that you are not draining the batteries.

[Rolind]

I have been reading up on this for the last several weeks as I am considering swapping my AGMs for battleborn GC2s. As near as I can tell, there are three issues; alternator protection, current moving from the trailer to the TV battery and adequate charging from the tow vehicle. There is information here and on BBs and victrons website that seems to suggest that
1). alternator protection with no more than three lithium batteries is not necessary
2). if a battery isolator or dc to dc charger is not used, there may be a small drain of the trailer batteries to the TV that is unlikely to be significant
3). If you really want good charging from the tow vehicle, you need a dc to dc charger and a more robust wire run from the alternator.
I would call or email BB and victron and see what they recommend. Pls keep us updated on their recommendations, I am very interested in what they say.

Also I know there are folks here that are much smarter than I on this issue, so pls chime in.

[dznf0g]

Originally Posted by Rolind

I have been reading up on this for the last several weeks as I am considering swapping my AGMs for battleborn GC2s. As near as I can tell, there are three issues; alternator protection, current moving from the trailer to the TV battery and adequate charging from the tow vehicle. There is information here and on BBs and victrons website that seems to suggest that
1). alternator protection with no more than three lithium batteries is not necessary
2). if a battery isolator or dc to dc charger is not used, there may be a small drain of the trailer batteries to the TV that is unlikely to be significant
3). If you really want good charging from the tow vehicle, you need a dc to dc charger and a more robust wire run from the alternator.
I would call or email BB and victron and see what they recommend. Pls keep us updated on their recommendations, I am very interested in what they say.

Also I know there are folks here that are much smarter than I on this issue, so pls chime in.

I would generally agree with those bullet points, with some caveats. (I have AGMs, but read up on Lithuims toward an eventual swap)

1) I suspect that if one's lithiums are substantially depleted when starting a charging run with the TV, that there "could" be some risk to the TV alternator. It depends heavily on the design of the particular TV electrical architecture. It is cheap to protect it.

2) I found when switching to AGM (the reasoning is the same for lithiums) that the necessary higher voltage charging requirements, and subsequent higher solar charging settings, there was a substantial backflow of current from the AS to the vehicle. This resulted in little charging of the AS batts during travel. I only have 200w of rooftop solar. None-the-less, you lose quite a bit of available AS charging.

3) This is true, certainly if you have a large lithuim battery bank. OP indicated he will only have 200Ah of battery, so not anywhere necessary for him, in particular, in most scenarios.

[jeffmc306]

You’ll get almost as many opinions on this topic as 1/2 ton vs. larger truck towing. One may feel comfortable while others are more conservative.

Victron has a good video on how not to blow up your alternator charging lithium batteries.

Some forum members recommend pulling the tow vehicle’s fuse to the 7-pin to avoid ruining their alternators because lithium batteries can draw higher voltages than an alternator can provide especially at lower RPM’s.

A DC-DC charger is a good way to avoid an unfortunate (and avoidable) situation. E-Trailer has several installation videos on their website that are very informative. They cover the gauge of wire required, Anderson connectors and properly fusing the postitive battery connection. Yes, it’s a lot of work to do it right but peace of mind when on the road.

If I had a lithium setup I would certainly install a good DC-DC charger but at least pull the 7-pin fuse if your budget is tight. Cheaper than a new alternator.

Good luck with your setup.

[Jack West]

Thank you (all) for the responses and suggestions. I have contacted Battleborn and will post their advice on this thread when I hear back from them.

[LilPeanut]

I have 600Ah of lithium and 1000w of solar. I added a Renogy Dc to DC 40A charger. I did not notice any TV drain or backfill before the charger, the wire is too small (and wire limits work in both directions).

We can run our batts down to 70% in the summer using the AC for a couple of hours at a rest area and sometimes solar isn’t available (rain/clouds). I ran welding wire from my second TV battery (have 2 and 2 alternators) and it seems to work when needed. It is also a (plan B or C for charging in case I need it.

I have not pulled the fuse to the 7 pin charging wire. All you read about the small wire size not being able to charge also works in the reverse. It would blow the little fuse before anything bad happens. So far, so good, maybe I am lucky.

[thewarden]

I installed the Victron 12-12-30 DC-DC charger in my 3500 Duramax and AS with 2 GC2 BB batteries for a couple of reasons.

I do not have solar and I do some boondocking. If you tried to charge 2 li batteries by way of the 7 PIN it will not happen, unless you are driving for several days. The stock 7 PIN is really no more than a trickle charge, maybe 2-3 amps.

I wanted to be able to take advantage of the truck's larger alternator capacity to charge lithium batteries, but keep my alternator and starting batteries safe.

The Victron charger can also be set for lithiums specific charging profile, ensuring that full charging is realized, but more importantly, that my batteries get the balancing charge they need to keep them healthy.

These BB batteries are not cheap and I wanted to be able to take full advantage of their extended capabilities and capacity. You can only do that if they are charged using the correct charging profile for lithiums. The DC-DC, correctly set up, does that.

[Bill M.]

A dc-dc converter would be a great thing to have. Seems like a small additional cost. But I doubt if necessary in that you can disconnect the charge wire on the 7 pin if you would rather. That will isolate the TV and the trailer.

[ROBERT CROSS]

Best way to avoid controversy here on the forums, if you think you need it, you better get it.

I didn't think I needed it, so I didn't get it.
No controversy here.

POI...I charge 360w of Zamp portables thru the 7pin.

Bob
🇺🇸

[uncle_bob]

Hi

First off, the "damage your alternator" videos are *not* talking about charging through a 7 pin connector. There is simply no way to damage an alternator via the normal 7 pin setup. None / no way / not going to happen. Then are talking about van installations that are done in a *very* different fashion.

If you are worried, simply disconnect the charge wire. Problem solved at near zero cost.

If you want to actually charge your lithiums via the 7 pin then you do need a DC/DC there just isn't any way around that. The charge voltage on the lithiums and the drop through the wires isn't going to allow you to charge without one.

Bob

[Life is a Highway]

Well like many topics read then do what you want.

Listen to the people that have them wired correct and know how to use them. Those that like the way the DC-DC safely performs.

Or listen to the people that absolutely hate them and find any excuse to trash them. They will be the ones with the passenger holding another solar panel angled to the sun out the side truck window.

I’ll filp a switch and while it's pouring rain or on a over cast day traveling I know the lithium batteries are getting topped within 4-7 hours, Have had quite a few discussions with Life Blue that seem to claim a DC-DC is not needed and the 5-7 amp shoelace trailer wire is all ya need. Good luck with that one. I’ll save my alternator for the truck.

Originally Posted by Jack West

I am taking delivery of a New Basecamp 20 next week. It will be fitted with two 100A Battleborn LiFePO4 batteries (and a Victron BMV712). I have a 180W solar suitcase I will use to keep the batteries topped up while camping and also Honda 1000W generator for additional juice if needed while camping. My TV ('06 Tacoma) has a 130 A alternator and I have charged my previous 3 trailers (all lead acid batteries) thru the 7pin on my Tacoma while towing. I have read and watched videos of folks with bigger lithium battery banks installing a DC-DC charger. I understand there are other threads where this is discussed, but I do not want to damage my TV battery or alternator while on my shakedown trip or towing the trailer 300 miles to its new home. I would appreciate any advice you can give me to avoid damage to either the AS batteries or the TV alternator/battery.

[Jimmyg561]

Ok here at what I did. I upgraded my alternator to a Macman 320 amp in my 2017 f-250 so I wouldn’t over tax the alternator, ran a separate 4ga. Fused wire with Anderson connectors to a 40 amp Renogy DC to DC charger installed inside the trailer. I have only two battleborn batteries. I believe there won’t be any issues as is and would try what you have and see how it works, you already have the generator if needed. My batteries are always 100% whenever I stop for the day.

[ROBERT CROSS]

Our Burb also has a high output alternator, the 7pin is not plugged in unless we are towing.
I wonder why the BB's are charged whenever we reach our destination?
Would they be more charged with a DCDC?
Bob
🇺🇸

[dznf0g]

Originally Posted by ROBERT CROSS

Our Burb also has a high output alternator, the 7pin is not plugged in unless we are towing.

I wonder why the BB's are charged whenever we reach our destination?

Would they be more charged with a DCDC?

Bob

[emoji631]

Robert, I can't remember if your year burb has a smart alternator. I dont think so. It appears to me that smart alternators are "out smarting themselves" in this application where there are mixed battery types which require higher voltages than the tv battery (AGMs and lithium).

[ROBERT CROSS]

Originally Posted by dznf0g

Robert, I can't remember if your year burb has a smart alternator. I don't think so. It appears to me that smart alternators are "out smarting themselves" in this application where there are mixed battery types which require higher voltages than the tv battery (AGMs and lithium).

Rich,
Like myself, I believe it's too old to be smart.
I installed the high output alternator so long ago I can't remember for sure just how high it is, 250 or 300a.

“Growing Old…being able to think about all the things you can no longer remember.”
RLC

Bob
🇺🇸

[Kanusport]

I have basically the same setup on my 22fb. I don't use a dc to dc. I disconnected the wire from the 7 way into the busbar on the trailer. If you search in here there are posts about this. Your trailer wiring diagram should help you.

[Jack West]

OK, so here is the response (in part) that I got from Battleborn when I sent them the same message as on my original forum post:


"Thank you for reaching out! Congrats on the new rig. So if you connected via 7pin. The wire gauge is typically around 10ga. So, you are only push around 5-8 amps through it to the batteries. Switching over to a DC to DC will allow you to charge at a higher rate if you want and keep your alternator safe. "

Bottom line; thank you all for offering the great (and varied) advice. I am comfortable that it is unlikely I will damage my 2006 TV "dumb" alternator by leaving the 7 pin hooked up while towing the new Basecamp. I don't intend at this point to get a DC-DC setup...just going to tow all hooked up like with past trailers and see what the result is...not concerned about actually fully charging the lithiums while on the road.

Thanks again for all the great input. Happy New Year all!

[uncle_bob]

Hi

A "smart" alternator will not do anything for the voltage at the 7 pin under load. It's targeted at the vehicle electronics up front.

The reason you disconnect the charge wire without a DC/DC is that your lithiums should be resting at 13.6V. Your alternator (smart or otherwise) may well drop back to 13.2 or lower as you chug through traffic. How low it goes depends on a lot of things. Any time it goes below 13.6, current flows *out* of your trailer batteries and into your TV. It may or may not be much current, but it is a discharge none the less.

Bob