Simple option for DC-DC charging from tow vehicle?

[sbsyncro]

I've searched and read a lot of posts and all discuss one of two scenarios: (1) charging directly from the 7-pin without a dC-DC controller or (2) running a heavy gauge wire pair from the tow vehicle to a dedicated high-amp connector on the trailer and using a high amperage DC-DC smart charger. I'm considering a simpler "hybrid" solution that seems to provide some benefit but eliminates the need for running that dedicated circuit & connector (and uses a much less expensive DC-Dc charger) but didn't find any previous posts that address my remaining question.

AOLithium 100 ah LiFePO battery mounted in my trailer will be charged in three possible ways:

1. Shore power: NOCO Genius 10x1 AC-DC charger with Lithium profile
2. Solar: Victron MPPT solar controller (also with Lithium profile)
3. Underway: Victron Orion TR 12/12 110w DC-DC charger with fixed voltage output that can be adjusted 10v-15v via pot.

Scenario #3 will use the existing 7-pin connector, which is rated to 15 amps according to the vehicle manual. The Orion unit simply acts as a voltage booster/regulator and is limited to 9 amps (110w). It will not be relied upon for restoring a deeply-discharged battery, but rather as a "top off/trickle charger" while transiting between camps.

QUESTION:

What voltage should I set the DC-DC charger’s output?

I assume it should be somewhere between 13.2v and 14.6v. This will be used during (potentially long) drives when the battery might already full, but most likely slightly discharged from light overnight use. Generally speaking, should the BMS cut off charging input when that is the case? if Max charge voltage on the LiFePO battery is 14.6v can one safely supply that voltage continuously, even if the battery is fully charged? (I have reached out to the battery MFR with the same question, and am waiting for their response).

Thanks in advance!

 

[justinm001]

Working on this now on a much larger scale with 6 converters. I learned that setting the output low then the batteries won't charge over like 80% but then use the dc to dc for actual loads. If I crank the voltage up it'll charge closer to 100%

 

[sbsyncro]

Working on this now on a much larger scale with 6 converters. I learned that setting the output low then the batteries won't charge over like 80% but then use the dc to dc for actual loads. If I crank the voltage up it'll charge closer to 100%

Interesting. There would never be a load in my scenario while charging from this DC-DC output, so not a factor for me. But it sounds like the voltage would need to be set to something more like 13.8 or 14.2.

My usage scenarios:

1. Parked at home in storage - on the AC-AC charger/maintainer
2. Driving to camp - battery will start full and hopefully "ignore" input from DC-DC charger. No loads as master switch is OFF
3. Camped - charging from 220w solar panel (48v) during daylight (only load is from LED lights, water heater ignition, water pump, and propane safety switch when galley is open).
4. Moving camp (or returning home) - battery will be slightly discharged from overnight use and will charge from DC-DC charger (ideally to 100%)

 

[justinm001]

Then you'd want to crank it up.

I'm surprised you wouldn't want the master switch on when driving to camp so the water heater and fridge and such is running getting things ready to camp. This would be a prime benefit as your batteries will be topped off when you leave then using the DC to dc charger to run those appliances while driving so when you get to camp the fridge is cold, water is warm and battery is 100.

 

[sbsyncro]

Then you'd want to crank it up.

I'm surprised you wouldn't want the master switch on when driving to camp so the water heater and fridge and such is running getting things ready to camp. This would be a prime benefit as your batteries will be topped off when you leave then using the DC to dc charger to run those appliances while driving so when you get to camp the fridge is cold, water is warm and battery is 100.

The fridge is in the back of the Jeep on a slide-out with its own dedicated 1500 wh battery and 200w solar panel. The propane water heater takes about 20 minutes to heat the 6 gals, and I don't like to drive with the propane tank opened anyway. By the time I'm set up, there is more than enough time to have the water hot if for some reason I need a shower right away. ;-)

Here's my typical setup - seeing this probably helps set the context. I use this rig as a remote hunting/fishing/exploring base camp usually dragged over rugged terrain to get as far away from civilization as possible.

 

[HRTKD]

3. Underway: Victron Orion TR 12/12 110w DC-DC charger with fixed voltage output that can be adjusted 10v-15v via pot.

Scenario #3 will use the existing 7-pin connector, which is rated to 15 amps according to the vehicle manual. The Orion unit simply acts as a voltage booster/regulator and is limited to 9 amps (110w). It will not be relied upon for restoring a deeply-discharged battery, but rather as a "top off/trickle charger" while transiting between camps.

In the Victron data sheet for that model it specifically says:

Adjustable output voltage Not intended for battery charging. Please consider using an Orion-Tr Smart for battery charging.

While the output of the converter is 9 amps, the input will likely be higher. More than the 15 amp source? Probably not, but it could be close.

The Tr Smart charger may be capable of having the output amps dialed down. I can do that on my Victron 100/50 solar charge controller.

 

[Brucey]

1. Shore power: NOCO Genius 10x1 AC-DC charger with Lithium profile

I would replace this with a Victron IP22 12/15, (15A) which is totally programmable via Bluetooth/Victron connect.

https://www.amazon.com/Victron-Energy-12-Volt-Battery-Bluetooth/dp/B08TRP71QM

 

[justinm001]

In the Victron data sheet for that model it specifically says:


While the output of the converter is 9 amps, the input will likely be higher. More than the 15 amp source? Probably not, but it could be close.

The Tr Smart charger may be capable of having the output amps dialed down. I can do that on my Victron 100/50 solar charge controller.

Exactly this. My 24-12 70a is 85a max and will pump out 85a for a while.

It's not designed as a charger because no charging profiles and just pumps out a constant voltage. This means you shouldn't expect to get to 100% just help charge

 

[sbsyncro]

Exactly this. My 24-12 70a is 85a max and will pump out 85a for a while.

It's not designed as a charger because no charging profiles and just pumps out a constant voltage. This means you shouldn't expect to get to 100% just help charge

Thanks. Thats pretty much all I expect - just something to bump the charge up a bit closer to full (although it would be great if it could take it to 100%)

@Brucey - I'd love to go all Victron, but I already had this NOCO charger, and I've had great luck with them in the past on cars, trucks, and boats. (I have a GenPro 10x4 on my boat).

 

[featherlite]

The Tr Smart charger may be capable of having the output amps dialed down

My understanding is that the output amps on the Orion-Tr-Smart cannot be dialed down. I would appreciate it if someone could confirm this.

 

[Brucey]

My understanding is that the output amps on the Orion-Tr-Smart cannot be dialed down. I would appreciate it if someone could confirm this.

That's correct.

 

[HRTKD]

That's too bad that the charge amps can't be dialed down. Bummer.

 

[0truck0]

The Dc to DC charger will do the thinking. Give it full power, let it reduce power to the battery (will it do that?).

I would not try to run big power draws off the tow vehicle, you can burn out the alternator. Charge the batteries while driving (keep them topped off not charged from zero), and if you have low draw like a DC compressor fridge (not propane fridge on electric) then that is fine too.

 

[featherlite]

big power

"Big power" is relative. Size the maximum draw of the DC to DC charger according the size and spare capacity of the vehicle's alternator. A general rule of thumb is not to pull more than 70% of the alternator's rated capacity. Sometimes, OEM wires may also need to be replaced with lower AWG wires (e.g., the "big three upgrade"). Due diligence and research is your friend. There are many detailed and helpful discussions on this forum.

 

[sbsyncro]

Coming back to this discussion after installing the Orion TR 12/12 -9 (isolated) into the trailer with some questions for the electrical gurus here. I'm getting an unexpected result that I am not able to figure out: (note this is not the "smart" version - the only thing adjustable is the output voltage via a trimming pot)

1. Input side is connected to trailer plug (+) terminal (rated at 15 amps from Jeep).
2. Output side is connected to LifePO4 battery in trailer
3. Output voltage adjusted to 14.6v per recommendation from battery mfg. measured before being connected to trailer battery

Resting voltage on trailer battery is 13.3v
Output from Jeep while running is around 14.1v (measured both at the trailer connection and the input side of the Orion)

Problem: I'm only getting 13.3v at the battery while the tow vehicle is running, despite the Orion's output being connected to the battery (which is 14.6v when not connected to the battery). I've also checked the BMS and verified that there is no current inflow to the battery (no charging effect).

Somehow I'm getting no contribution from the Orion, despite it seeming to perform as expected when not connected to the battery.

For those that are going to say "you should have gotten the Smart version - thats a "real" DC-DC charger", yes, I know that would have been ideal, but (1) it would not have fit the space (2) I was trying to KISS and (3) trying to keep costs down and the extra $100 is not something I wanted to spend, as I really only intended this as a "trickle charger" type solution while underway (read my original post at the beginning of the thread). I have friends successfully using this approach, so I can't understand why my setup isn't working.

Thanks in advance for any advice.

 

[HRTKD]

I don't have an Orion but I'll throw this out: With no current (Orion output not connected to anything except a volt meter) the voltage can float up to the max. With current, the voltage is going to go down. Eventually, if you left the tow vehicle running long enough you would see voltage rise up to 14.6 and current go down to almost zero.

However, if the BMS is reporting zero current going in, is it possible that you have a load (other than the battery) that is getting the current?

 

[justinm001]

This is because your batteries are charged. The Orion won't charge your batteries to 100% and depending on how turned up that pot is will determine how much it'll charge. Mine typically will charge to around 80% then it'll use the Orion for loads and keep the battery at idle.

I have 6 of these Orions and currently playing around with the pot setting to see. You should be able to turn it all the way up without worrying about any issues as you have a battery to absorb the voltage.

My understanding is if you didn't have a battery and used it just for loads it'll adjust the output voltage but when it's connected to a battery it'll adjust how much to charge the battery before keeping idle. Not sure how this works technically but I believe the voltage needs to be X volts above the battery to actually charge.

 

[sbsyncro]

I don't have an Orion but I'll throw this out: With no current (Orion output not connected to anything except a volt meter) the voltage can float up to the max. With current, the voltage is going to go down. Eventually, if you left the tow vehicle running long enough you would see voltage rise up to 14.6 and current go down to almost zero.

However, if the BMS is reporting zero current going in, is it possible that you have a load (other than the battery) that is getting the current?

[Is there a way to multi-quote in replies...?]

I tried putting a 1200 watt load on the battery while the tow vehicle was running and I still didn't see a change. Perhaps I will try drawing down the trailer's battery to 50% or 70% SoC and see if there is a difference. Thanks for the tip - this is something I thought about as a possibility as well. Should be easy enough to test

 

[sbsyncro]

This is because your batteries are charged. The Orion won't charge your batteries to 100% and depending on how turned up that pot is will determine how much it'll charge. Mine typically will charge to around 80% then it'll use the Orion for loads and keep the battery at idle.

I have 6 of these Orions and currently playing around with the pot setting to see. You should be able to turn it all the way up without worrying about any issues as you have a battery to absorb the voltage.

My understanding is if you didn't have a battery and used it just for loads it'll adjust the output voltage but when it's connected to a battery it'll adjust how much to charge the battery before keeping idle. Not sure how this works technically but I believe the voltage needs to be X volts above the battery to actually charge.

[Is there a way to multi-quote in replies...?]

Thanks - are you using the "dumb" ones like this (not the "Smart" versions, so I guess they are dumb...). I will try discharging the battery down to 50% and see if that changes things. I think what you're saying is that the BMS is preventing any current to flow in from the Orion because it is at "full" SOC.

 

[justinm001]

[Is there a way to multi-quote in replies...?]

Thanks - are you using the "dumb" ones like this (not the "Smart" versions, so I guess they are dumb...). I will try discharging the battery down to 50% and see if that changes things. I think what you're saying is that the BMS is preventing any current to flow in from the Orion because it is at "full" SOC.

Yes I'm using the dumb ones. 4x 24/48 8.5a and 2x 24/12 70a

It's not the bms but the voltage has to be high enough to charge the batteries. Turn the pot all the way up and see what happens, along with drain the batteries down. This is all very simple to see if you have a shunt like victrons smartshunt.