What performance difference can I see with a DC to DC converter?

[hikingcamera]

Just tried it again this morning at 52% and got a tad less, about 1.7 or so amps going into my trailer from the 7-pin. The tried at 42% (12.9 volts) and it got 3.5. Still seems like the DC to DC will be worth it.

[Llittle54]

[QUOTE=hikingcamera;2634911]Wow, I apparently can't go 48 hours without burning through all 200aH of our Lithium Battleborn batteries. And we were pretty conservative with our usage. I don't understand how we went through power that quickly... It was not like that in our old trailer with 200aH of AGMs...[/

Hmmmm,
200Amh Renogy
Weather was cool but not cold. Only ran the furnace at most a couple hrs in the am.
I did use my inverter, some. I only installed a 350w. The only regular draw is the tv to watch a movie or two.
I paid attention to my light use but not obsessively.
Could have managed it hour charging via the Dc-Dc but I wanted to try it.
I got down to 42% so I still had a couple of days of power left!
I’d love to hear your and other’s thoughts on battery life and what the differences might be in our respective cases.

[dznf0g]

Originally Posted by hikingcamera

Just tried it again this morning at 52% and got a tad less, about 1.7 or so amps going into my trailer from the 7-pin. The tried at 42% (12.9 volts) and it got 3.5. Still seems like the DC to DC will be worth it.

I think you would be pleased. 18 amp isolated model if using the umbilical.

[hikingcamera]

Originally Posted by Llittle54

Hmmmm,
200Amh Renogy
Weather was cool but not cold. Only ran the furnace at most a couple hrs in the am.
I did use my inverter, some. I only installed a 350w. The only regular draw is the tv to watch a movie or two.
I paid attention to my light use but not obsessively.
Could have managed it hour charging via the Dc-Dc but I wanted to try it.
I got down to 42% so I still had a couple of days of power left!
I’d love to hear your and other’s thoughts on battery life and what the differences might be in our respective cases.

Is your fridge Propane or electric only? That seems to be a defining difference for a lot of folks. I know that we have not had much solar charging for most of our boondocking trips so far. We had some more this trip, but with the low sun at this time of year, it still probably wasn't a ton. I also brought our Goal Zero which extended us a bit, probably would have given us an extra day compared to last time. We didn't drive enough to recharge it much though.

Originally Posted by dznf0g

I think you would be pleased. 18 amp isolated model if using the umbilical.

Cool. This sounds like a good pathway. Thanks!

[Jcondon]

Originally Posted by hikingcamera

Is your fridge Propane or electric only? That seems to be a defining difference for a lot of folks. I know that we have not had much solar charging for most of our boondocking trips so far. We had some more this trip, but with the low sun at this time of year, it still probably wasn't a ton. I also brought our Goal Zero which extended us a bit, probably would have given us an extra day compared to last time. We didn't drive enough to recharge it much though.




Cool. This sounds like a good pathway. Thanks!

I would shoot for the stars. Buy at least a 30 amp DC to DC charger and see what you get with the existing wiring. You will be pleased. But a small upgrade on wire size in the tow vehicle may put you into the 25 amp range? It's totally feasible. You will see probably 10 volts 30 amps on the inlet and 22 or so at 14.6 volts on the outlet. That would please me for sure.

[dznf0g]

Originally Posted by Jcondon

I would shoot for the stars. Buy at least a 30 amp DC to DC charger and see what you get with the existing wiring. You will be pleased. But a small upgrade on wire size in the tow vehicle may put you into the 25 amp range? It's totally feasible. You will see probably 10 volts 30 amps on the inlet and 22 or so at 14.6 volts on the outlet. That would please me for sure.

No! A 30 amp model will pull in excess of 30 amps, due to inefficiency in the system. This will, at a minimum, blow fuses on your 30 amp circuit.

[uncle_bob]

Hi

As the batteries charge, their voltage goes up. If you get 2A at 13.2V / 70%, you will get significantly less current if the batteries get to 80%. If they drop down to 60% you will get a bit more current. Because of this, there is no quick and easy way to estimate the charge you get in some number of hours driving.

Bob

[dznf0g]

Originally Posted by uncle_bob

Hi

As the batteries charge, their voltage goes up. If you get 2A at 13.2V / 70%, you will get significantly less current if the batteries get to 80%. If they drop down to 60% you will get a bit more current. Because of this, there is no quick and easy way to estimate the charge you get in some number of hours driving.

Bob

Correct. From a personal practical standpoint, I have an 18 amp DC-DC, 2 X 125 amp AGM batteries and the stock 30A umbilical hookup. Since I got my new phone, I can now monitor the app from the cab. When I was at 75% of total battery capacity, I saw the full 18 amps for about 30 - 45 minutes. Then the current output started marching downward. After about 2 additional hours, it went into absorption. by noon it was full.

HOWEVER!!!! I also have 200 watts of solar on the roof of the AS, running the exact same custom Victron program, and the outputs are very close to cumulative. So the DC-DC times in the circuit described above will be about 50 - 75% longer with DC-DC alone...and depending on solar conditions.

[richard5933]

Not sure about other models, but Victron rates their DC-to-DC chargers on the output side, meaning that it could possibly pull more than that on the input side.

[dznf0g]

Originally Posted by richard5933

Not sure about other models, but Victron rates their DC-to-DC chargers on the output side, meaning that it could possibly pull more than that on the input side.

And they do. As much as 4 amps more, depending upon conditions. That's why, I believe Victron chose such an "odd" number for the 18 amp model. Why not have a 20 amp and 30 amp...even number lineup? (I think the do have a 20 amp model as well)

Because....circuits are supposed to have a 20% safety margin relative to actual load vs. circuit designed capacity. That makes a 30 amp circuit designed for a 24 amp continuous load. A 20 amp DC-DC drawing 24 amps is too close for comfort in actual, widely varying applications and condition of aging circuits....so I believe they chose 18 amps to account for variation in systems in the marketplace.

[Jcondon]

Originally Posted by richard5933

Not sure about other models, but Victron rates their DC-to-DC chargers on the output side, meaning that it could possibly pull more than that on the input side.

Renogy and some others have a current limiting terminal that limits the current to 50% of rated capacity. My thinking is to go a bit bigger and limit the current with a jumper. Then if you upgrade the charge wire you can then pull the jumper for full rated current. Victron may not offer this option. They want you to buy a new one.
LC Current Limit Wiring
The DC-DC battery chargers feature 50% current limiting from the rated specification when
connecting the LC Terminal to a 12V source. Current Limiting is instant and recommended to
be connected to the same location as the D+ ignition cable. Alternatively, you can toggle
current limiting to your liking by connecting the LC terminal to starter battery positive terminal.
In this fashion, current limiting will always take until removing the LC wire from the battery
terminal to revert to the normal amp rating. Use 18-16AWG copper cable for the LC terminal
and you may need to splice your own connections for the other cable end depending on your
connection point.

[dznf0g]

Originally Posted by Jcondon

Renogy and some others have a current limiting terminal that limits the current to 50% of rated capacity. My thinking is to go a bit bigger and limit the current with a jumper. Then if you upgrade the charge wire you can then pull the jumper for full rated current. Victron may not offer this option. They want you to buy a new one.
LC Current Limit Wiring
The DC-DC battery chargers feature 50% current limiting from the rated specification when
connecting the LC Terminal to a 12V source. Current Limiting is instant and recommended to
be connected to the same location as the D+ ignition cable. Alternatively, you can toggle
current limiting to your liking by connecting the LC terminal to starter battery positive terminal.
In this fashion, current limiting will always take until removing the LC wire from the battery
terminal to revert to the normal amp rating. Use 18-16AWG copper cable for the LC terminal
and you may need to splice your own connections for the other cable end depending on your
connection point.

That's a nice feature, but I am partial to Victron for all the electrical control side equipment. I do have Renogy panels and like them quite well, after some 8 or 9 years on the roof of the AS.

[Jcondon]

Originally Posted by dznf0g

That's a nice feature, but I am partial to Victron for all the electrical control side equipment. I do have Renogy panels and like them quite well, after some 8 or 9 years on the roof of the AS.

I like and use them both. Whichever one has the features that I desire than that is what I choose. Renogy is pushing the envelope a bit harder lately I think. I like their Smart Lithiums a lot.

[jnm30327]

My thinking went like this:

1. The available charging amps through the 7 pin was inadequate.
2. So a separate set of wires from the TV battery to the rear of the truck was necessary.
3. If I was going to go to the trouble of running those wires, I may as well make them large enough to power a 30 amp DC-DC charger. 30 amps was a load well handled by the TV alternator.

With 30 amps of input, it is enough to run the old style AC/LP refrigerator or to charge a battery. Why go for 18 when, for a few dollars more, you can have 30 amps?

[richard5933]

Originally Posted by jnm30327

My thinking went like this:

1. The available charging amps through the 7 pin was inadequate.
2. So a separate set of wires from the TV battery to the rear of the truck was necessary.
3. If I was going to go to the trouble of running those wires, I may as well make them large enough to power a 30 amp DC-DC charger. 30 amps was a load well handled by the TV alternator.

With 30 amps of input, it is enough to run the old style AC/LP refrigerator or to charge a battery. Why go for 18 when, for a few dollars more, you can have 30 amps?

All things being equal, I agree with you.

Alternator capacity can of course play a part in this, and sometimes the way things work out it's not always possible to jump straight to the larger DC-to-DC charger. I installed my DC-to-DC charger before I had decided to run new wiring to the rear bumper. My goal was to get things on the road and start using the rig to test the function & capacity of things. After seeing the wiring limitations, I ran a pair of 6 ga wires from the battery to the back bumper. When my alternator died (due to an unrelated problem) I upgraded it to to a higher output model to provide enough spare capacity for a future DC-to-DC upgrade. I'm still using the 12/12-18 DC-to-DC charger but plan to upgrade that at some point in the future now that I've got the ability to use a larger one.

[Kawboy01]

As others have replied the 7 pin will only provide a minimal amount of charge current for the lithium batteries you have. On our 21GT27FBQ with solar the 180 watts solar, we installed 2 SOK 206 lithium and the 7 way just didnt cut it. I ran 4 gage weld cable from TV battery thru a 40amp breaker to the rear where I connected a Renogy 20amp DC2DC charger mounted in the front compartment of the AS with an Anderson connector and more 4 gage cable. I pulled the fuse that provided the power to the 7way so we dont need to pull the plug when overnighting. We could have gone bigger on the DC2DC but with the solar and the way we travel the 2 SOK's get plenty of charge. I would definitly recommend a DC2DC charger.

[Llittle54]

Here’s a twist. I have installed a Renogy 30 Dc-Dc and run new 4awg wire. I connect to my truck via an Anderson coupler. Can I charge my batteries by attaching my portable solar panel that has its own solar controller by connecting to the dc-dc Anderson connector to my trailer. Again can I charge my batteries with a portable panel through the Renogy?
Should the portable panel’s solar control stay or be removed?

[1StreamDream]

I just finished wiring in my Victron 12-12-18 DC-CD isolated charger, but the operating behavior is puzzling to me. When I connect with the 7-way, with the truck engine running, I am not getting anything on the 7-way wire (mere millivolts). I am sitting parked in my driveway, and I know some folks have reported "smart" behaviors from the tow vehicle side, but I am unsure why I don't get any 12VDC on that wire. To conform the rest of my setup, I connected +12V from a battery to the input side of my charger, it immediately powers up, I can connect via bluetooth, and I have it configured to be a charger. Anybody know why I might not get voltage on the 7-way wire ? In case it matters, my tow vehicle in this case is a 2021 F-250 (gas engine). Thanks in advance for any troubleshooting help.

[uncle_bob]

Hi

On a typical modern Ford truck, you have to get it up to something like 5 or 10 MPH and then put on the brakes. Once you do, it will enable the charge wire. Are there other ways to turn it on? there may well be .....

Bob

[IrisnGerald]

Perhaps a silly question …

How does it effect fuel mileage?

The trucking industry looked into more efficient alternators to reduce fuel costs. Seems like adding a load to the alternator would be the inverse.

Link … https://www.ttnews.com/articles/effi...ts-experts-say