DC-DC charger as an alternative to generator?

[Martinjmpr]

Last month camping in Oregon in our new-to-us travel trailer (2021 Rockwood Geo Pro 19BH) we had an issue with electrical power. The trailer was bought used and the (original equipment) batteries were pretty much worn out. They are two x 12v Interstate FLA batteries.

We were boondocking (no hookups) and with cloudy skies and 200' trees, our solar panels were useless. Worried about losing power, I decided to use a "redneck generator", i.e. I just hooked jumper cables from my truck (2018 F-150) to the trailer battery terminals and ran it for an hour or so. That gave us enough power to get through the day (biggest draw is the 12v fridge.)

Now I'm about to upgrade to LiFePo4 batteries and we are embarking on a multi-week trip through the Southeast. Most of the time we will be camping without hookups.

I was on the brink of buying a generator (which we haven't needed so far in 12+ years of camping) but then a thought occurred to me: While I know I can't just hook jumper cables to a Lithium battery, there ARE a lot of DC-DC chargers out there of varying capacities.

So I'm thinking: If my batteries start to get depleted, I could just hook a DC-DC charger from my tow vehicle to the lithium batteries. Make sure the battery charger's charging profile is set to "lithium" and then just run the truck to charge the batteries.

Waste of gas? Maybe, but the cost of gas and a DC-DC charger is still likely to be WAY less than a 2200w inverter generator (they seem to start around $500 and go up from there.)

So I'm asking the hive-mind here: Is there any reason this WOULDN'T work? And what have I not thought of?

Anyone else tried this?

 

[Dave in AZ]

Last month camping in Oregon in our new-to-us travel trailer (2021 Rockwood Geo Pro 19BH) we had an issue with electrical power. The trailer was bought used and the (original equipment) batteries were pretty much worn out. They are two x 12v Interstate FLA batteries.

We were boondocking (no hookups) and with cloudy skies and 200' trees, our solar panels were useless. Worried about losing power, I decided to use a "redneck generator", i.e. I just hooked jumper cables from my truck (2018 F-150) to the trailer battery terminals and ran it for an hour or so. That gave us enough power to get through the day (biggest draw is the 12v fridge.)

Now I'm about to upgrade to LiFePo4 batteries and we are embarking on a multi-week trip through the Southeast. Most of the time we will be camping without hookups.

I was on the brink of buying a generator (which we haven't needed so far in 12+ years of camping) but then a thought occurred to me: While I know I can't just hook jumper cables to a Lithium battery, there ARE a lot of DC-DC chargers out there of varying capacities.

So I'm thinking: If my batteries start to get depleted, I could just hook a DC-DC charger from my tow vehicle to the lithium batteries. Make sure the battery charger's charging profile is set to "lithium" and then just run the truck to charge the batteries.

Waste of gas? Maybe, but the cost of gas and a DC-DC charger is still likely to be WAY less than a 2200w inverter generator (they seem to start around $500 and go up from there.)

So I'm asking the hive-mind here: Is there any reason this WOULDN'T work? And what have I not thought of?

Anyone else tried this?

Everyone who has ever bought a dc2dc charger has tried this, you are on the right path. All successfully. Many are finding they no longer need solar.

There are probably 1000 threads on this at various forums including this one. And 10,000 youtube videos.

Here's my recent one using Pecron car charger, a nice dcdc charger. In this I'm charging my powerstation, but you could use any basic dcdc charger like Victron and do a 2nd House battery system.

Click the little link in center of black "watch on youtube"

 

[Martinjmpr]

Everyone who has ever bought a dc2dc charger has tried this, you are on the right path. All successfully. Many are finding they no longer need solar.

There are probably 1000 threads on this at various forums including this one. And 10,000 youtube videos.

Here's my recent one using Pecron car charger, a nice dcdc charger. In this I'm charging my powerstation, but you could use any basic dcdc charger like Victron and do a 2nd House battery system.

Click the little link in center of black "watch on youtube"

Thanks for the info. BTW I watched your video about the Licitti battery box and I'm stoked about that. I've been using a power box based on a trolling motor case and this seems to be a significant upgrade at a very reasonable cost.

Silly question WRT charging LiFePo4 batteries: The battery I'm looking at has a "recommended" charge current of 20A max. Does that mean that using a 30A charger would be a bad idea? It's just that 20A seems like a slow charging rate (4 hrs to charge a 100AH battery at 20% to full charge) or am I missing something WRT lithium batteries? Should I shop around and find a battery that can be charged at a faster rate?

 

[Ozarker]

Yes, it's a bad idea, the recommended 20A charge rate should not be exceeded, you could burn the house down.

Quicker to charge = quicker to discharge.

As to "WRT" is that a brand, are you introducing the topic or do you mean wireless router technology? @Martinjmpr

 

[Dave in AZ]

Thanks for the info. BTW I watched your video about the Licitti battery box and I'm stoked about that. I've been using a power box based on a trolling motor case and this seems to be a significant upgrade at a very reasonable cost.

Silly question WRT charging LiFePo4 batteries: The battery I'm looking at has a "recommended" charge current of 20A max. Does that mean that using a 30A charger would be a bad idea? It's just that 20A seems like a slow charging rate (4 hrs to charge a 100AH battery at 20% to full charge) or am I missing something WRT lithium batteries? Should I shop around and find a battery that can be charged at a faster rate?

The question is the Max Charge rate, not recommended, should be around 1C, 100A. Then most will recommend a slower rate, but can do faster.
A 100Ah LFP battery today should in general have a BMS allowing 100A discharge. That is called 1C, its max discharge rate, you use this to decide what it can support. Like a 12v 100A LFP could support theoretically a 1200W inverter, but really 1000W. But you'd likely design for less, like 800W.
Anyways, that LFP should also have a max charge rate of around 50A, though it CAN do the full 100A usually.

When you're posting a thread like this, don't dance around what the product is, "the battery I'm considering " etc, it helps no one to help you. STATE THE BATTERY PRECISELY AND ALL KNOWN INFO! Then people don't have to look it up, and can actually help you

Almost every 100Ah battery I look at, has a 100A discharge BMS. Redodo for instance, which I have a Mini of, every single 12v recommends 0.2C charge rate, 20A. HOWEVER THEY ARE ALL CAPABLE OF A FULL 100A continuous charging! Pretty much everyone recommends 0.2c for a nice even charge that keeps cells in balance over time. This is generally not restrictive. Like, if you have solar and sun available, charge away up to 1C.

 

[Dave in AZ]

Yes, it's a bad idea, the recommended 20A charge rate should not be exceeded, you could burn the house down.

Quicker to charge = quicker to discharge.

Uhmm... I'm gonna say disregard this, look at battery specs. Recommended charge is all about cell balance and battery longevity, not battery catching fire. I wouldn't make a habit of charging at 1c, but most allow a continuous 1c rate.

There are some design best practices and standards, how much panel and charge amps vs BMS rates etc.

For the OP, You can get all the info you need, here, it will be your best place for solar and battery answers:

Vehicle Mounted Systems

RV's, Vans, Trucks and More! Typically 12v, and 100-1000w, but the limits are endless!

diysolarforum.com

But yeah... pretty much every LFP battery recommends 0.2c charge rate, it is what the current cells like best to all stay balanced and avoid issues of one charging faster than others and being cut out by BMS until you've balanced them all.

I use, and recommend, the Victron ip67 Victron Ip67 12v 25A

 

[Pacific Northwest yetti]

DC/DC works, well, I love my victron.
On my pop up,
My brother has a shop in Reno that does these. Just make sure and size the guage for voltage drop, breakers both sides, and a big anderson plug will work. Works well for tow behinds as well.

 

[craig333]

Not sure why you'd use it instead of solar unless you're constantly one the move. Mine gets used only when the solar isn't cutting it which is rare. Nice to have as a backup charging source though.

 

[Dave in AZ]

Not sure why you'd use it instead of solar unless you're constantly one the move. Mine gets used only when the solar isn't cutting it which is rare. Nice to have as a backup charging source though.

Lots of reasons folks might. Maybe not all apply to a travel trailer guy. But you're right, it is a good backup to solar.

Here are a few for me:
1. Arizona, hot... if I don't camp in the shade, my truckbed camper will be 120F, fast. So fixed solar isn't a strong option.
2. Mobile solar panels not good either, pain to store and deploy, would need 60ft of cord, 6awg min, for all campsites really.
3. Weight, Tacoma payload 1100 lbs, I don't have 60-100 lbs extra payload for a "might work out that day" energy option.
4. Cost and reliability. 2 hrs of driving/charging replaces a full day of sitting in sun for a full roof of panels.
5. Assurance. Replaces a generator, again a couple hours of idle can refill my battery if needed.

I do have 460W of portable panels, but I've stopped even bringing them. My dc2dc charger has pretty much removed my need for any solar setup at all, in my overlanding and truck camping. And I'm switching to electric cooking too, even so I haven't needed the solar. A lot of folks have found this recently.

 

[Martinjmpr]

Not sure why you'd use it instead of solar unless you're constantly one the move. Mine gets used only when the solar isn't cutting it which is rare. Nice to have as a backup charging source though.

The trailer has a solar panel but we learned the hard way that there are places where solar is worthless. We camped in Oregon in September. Cloudy skies and 200' canopy trees all around us (and we were literally camped at lake side!)

The other drawback to solar is the slow charge rate unless you have a whole mess of panels. I could probably put 2 more 100w panels on the roof of the trailer but even then I'd be looking at a maximum of maybe 16 - 20A and only for as long as the sun was up. We are planning a camping trip to the Southeast in November - December that will likely see us under very heavy tree cover, cloudy days and very short days. So while solar is nice, it's better to have something that can work when solar can't.

 

[Martinjmpr]

When you're posting a thread like this, don't dance around what the product is, "the battery I'm considering " etc, it helps no one to help you. STATE THE BATTERY PRECISELY AND ALL KNOWN INFO! Then people don't have to look it up, and can actually help you

Almost every 100Ah battery I look at, has a 100A discharge BMS. Redodo for instance, which I have a Mini of, every single 12v recommends 0.2C charge rate, 20A. HOWEVER THEY ARE ALL CAPABLE OF A FULL 100A continuous charging! Pretty much everyone recommends 0.2c for a nice even charge that keeps cells in balance over time. This is generally not restrictive. Like, if you have solar and sun available, charge away up to 1C.

Fair enough. This is what I'm looking at getting unless someone can think of another one in a similar price range that is better:



Self-heating because it will be mounted on the outside of our trailer and we live in Colorado. I like that it has a built in SOC monitor that also works on Bluetooth.

If I'm understanding it correctly, this should mean no need for a shunt to measure SOC and power use, is that right?

 

[Martinjmpr]

As to "WRT" is that a brand, are you introducing the topic or do you mean wireless router technology? @Martinjmpr

Sorry, I thought that was a common term.

WRT = "With Regard To" 😉

 

[Dave in AZ]

Fair enough. This is what I'm looking at getting unless someone can think of another one in a similar price range that is better:

View attachment 857182

Self-heating because it will be mounted on the outside of our trailer and we live in Colorado. I like that it has a built in SOC monitor that also works on Bluetooth.

If I'm understanding it correctly, this should mean no need for a shunt to measure SOC and power use, is that right?

Thx. That looks decent, 269 about right for heated bluetooth. 100A bms, all looks pretty standard.

I myself would go with more battery. That is just 1280Wh, probably 1200 usable, you don't want to drain to bms shutdown.
45W fridge, 24 hrs= 1080Wh
60W LED lights, 5 hrs, 300Wh
Diesel heater, 30W 10 hrs, 300Wh
Etc, it adds up. I'd get at least 200Ah and be sure you do an accurate energy audit of your usage.

 

[Martinjmpr]

Thx. That looks decent, 269 about right for heated bluetooth. 100A bms, all looks pretty standard.

I myself would go with more battery. That is just 1280Wh, probably 1200 usable, you don't want to drain to bms shutdown.
45W fridge, 24 hrs= 1080Wh
60W LED lights, 5 hrs, 300Wh
Diesel heater, 30W 10 hrs, 300Wh
Etc, it adds up. I'd get at least 200Ah and be sure you do an accurate energy audit of your usage.

Ah, I didn't say this at the outset but I'll be getting 2 of them, wired in parallel.

We don't have a diesel heater in our trailer, there is a propane heater that uses a fan though so it does have some draw. Not exactly sure how much though. The fridge is the biggest draw. There is also a 1000w inverter that I'm thinking of removing because I see no need for it. It stays turned off.

 

[Dave in AZ]

What @klahanie said. 40A charger gives 20A to each parallel battery.

Also... you see what I meant about providing info in your post, not keeping secrets from your helpers? I wasted all my time typing out loads to convince you 100A wasn't enough. If you were a neighbor, I'd probably stop loaning you tools now...