Charging while towing

[Sparksalot]

For those of you using a DC-DC charger for a trailer, where do you locate the charger? How are you doing the ignition sense?

[bdosborn]

That Renogy seems to be priced right for $100 on Amazon. I've got a 12v 40ah LifePO4 now but I'm thinking that maybe down the road changing it out for a 12v 100ah LifePO4. Will that 20A DC-DC charger be suitable for both cases or should I go with something like a 40a or 50a right off with going with the 100ah down the road..? Is there any relationship to battery ah compared to amp rating for DC-DC chargers..?

There's a hard and fast answer; it depends.
It depends on how much energy you use in a day, how much you drive everyday, how big your alternator is, how big the wiring is back to your trailer plug, how much solar you've got.

What I would do is get a battery monitor so you can track how much energy you use in a day. Then you can make some good decisions on how big your battery and charger should be. A few of us have been using this in our campers Ali Battery Monitor. Its not expensive and it will really help you understand how big you need to size components.

Finally, there isn't a relationship between battery capacity and charger rating like there is with your AGM battery, LiFePO4 batteries don't care what rate you charge them.

Bruce

[bdosborn]

For those of you using a DC-DC charger for a trailer, where do you locate the charger? How are you doing the ignition sense?

The DC-DC charger is just like a PV controller, put it as close to the battery as possible so that voltage drop isn't an issue. I have my ignition sense setup a little different in the trailer, I use the driving lights to turn the charger on and off. In the van I use a Victron DC-DC charger and it has a smart sensor that will monitor the battery voltage and turn itself on and off.

Bruce

[cdnred]

On my 12v circuit, I plan to be only running my CPAP at nite and possibly a couple of interior lights periodically not a heavy load. When traveling, I plan on going 5-6 hours from one spot to another. So if there isn't any relationship between DC-DC charger size to battery ah then I'd assume that the 20ah DC-DC charger would be suitable for both the 40ah and 100ah batteries. When hooked up to shore power when available at campgrounds I'd be running everything off the 110v shore power with no need for 12v..

Do you have any preference between Renogy compared to Victron Energy Orion-Tr Smart..? I like the fact that the Victron Energy Orion-Tr Smart has blue-tooth capability yet the Renogy is rated highed in reviews and is much cheaper..

Wiring in the 20a DC-DC charger, is there anything else I would need to buy to complete the circuit..?

Helmuth

[bdosborn]

Do you have any preference between Renogy compared to Victron Energy Orion-Tr Smart..? I like the fact that the Victron Energy Orion-Tr Smart has blue-tooth capability yet the Renogy is rated highed in reviews and is much cheaper..

Wiring in the 20a DC-DC charger, is there anything else I would need to buy to complete the circuit..?

If the Renogy works then it's fine, if it doesn't they have a terrible reputation when it comes to honoring a warranty. The Victron has a better reputation both for reliability and honoring warranties. And I'm a tech nerd so I like the Bluetooth capability.

Don't forget a fuse, you'll need to read the manual to see what they recommend.
Bruce

[cdnred]

Do you have any preference between Renogy compared to Victron Energy Orion-Tr Smart..? I like the fact that the Victron Energy Orion-Tr Smart has blue-tooth capability yet the Renogy is rated highed in reviews and is much cheaper..

Wiring in the 20a DC-DC charger, is there anything else I would need to buy to complete the circuit..?

If the Renogy works then it's fine, if it doesn't they have a terrible reputation when it comes to honoring a warranty. The Victron has a better reputation both for reliability and honoring warranties. And I'm a tech nerd so I like the Bluetooth capability.

Don't forget a fuse, you'll need to read the manual to see what they recommend.
Bruce

[featherliteCT1]

Will that 20A DC-DC charger be suitable for both cases or should I go with something like a 40a or 50a right off

If it were me, I would ascertain how many Ah my alternator is rated for, apply a 70% useable/safety factor to that number, start the tow vehicle, then put an Ah clamp meter on one of the starter battery cables, then record the Ah drawn at idle, then start turning on accessories recording the cumulative Ah as each accessory is turned on. Then, compare the cumulative Ah draw number to the 70% Ah number, with the difference in Ah being how many spare Ah I could draw from the alternator to charge the house battery. Over taxing an alternator will eventually burn up the alternator.

I tow with a 1/2 ton Chevy pickup truck with an alternator rated at 150Ah. After performing the above testing, I opted for a Victron Tr Smart DC-DC charger that out puts 18Ah. Also, I did not want to upgrade my 6AWG OEM truck starter battery wires to a larger gauge to accommodate the increased Ah draw.

[bdosborn]

That's an important point: the capacity of an alternator at idle is nowhere close to the full rating. Maximum output is around 6,000 RPM but idle speed is around 1,500. So an alternator that is rated at 120A has a typical idle capacity of 50A. Unless you have a truck with a high output alternator you need to be careful with how big a DC-DC charger you add to your trailer. I wouldn't charge at idle for a long time, even with a high capacity alternator, as they run hot from the low airflow. Don't let the magic smoke out!
Bruce
https://www.lifewire.com/understanding-alternator-output-ratings-534785

[cdnred]

I was told that a 20ah DC-DC charger would take approximately 2 hours to charge a 40ah LifePO4 battery from dead or approximately 5 hours to charge a 100ah LifePO4 battery from dead. So I'm thinking that the 20ah charger at $169 for the Victron Energy Orion-Tr Smart on Amazon should be suitable for my needs. If I were to go with a 12v 100ah AGM battery then I wouldn't need to go with a DC-DC charger. Pricing out a 12v 100ah AGM battery would run about $175-$300..

The 100ah AGM battery could safely run down to ~20% of it's capacity giving me about 80ah of use. The 12v 40ah LifePO4 that I have now I can safely run down to ~2% of it's capacity or 1ah before recharging to give me 39ah of use. With the 100ah LifePO4 I could safely run it down to 2ah before recharging giving me 98ah of use. A 12v 100ah LifePO4 battery I could pickup for ~$198 which would give me more usable ah for my needs. The cost of the 100ah AGM is more or equal to the cost of the 100ah LifePO4.

Based on that, would I be better off to install the 20ah DC-DC charger to the 40ah LifePO4 I have now..? Down the road when needed I can just swap out the 40ah LifePO4 with the 100ah LifePO4 and keep using the same 20ah DC-DC charger. If I keep the 40ah LifePO4 I have now, I'd need to buy the 20ah DC-DC charger to maintain it. If I choose not to buy the DC-DC charger, then I would need to buy the 100ah AGM battery. Sitting on the fence on which way to go, adding an extra $25 to the cost of the DC-DC charger and go with a AGM battery. Would it be a smart choice to include the DC-DC charger for both the AGM and LifePO4 batteries..? If the case is that it should be included for both the AGM and LifePO4, then it would be better for me to stay with the LifePO4 battery setup I have now and add the DC-DC charger to my current setup..

Between the Renogy and the Victron Energy, I'm leaning more towards the Victron for the blue tooth feature and the positive customer support. The 20ah DC-DC charger does it come with a feature that once it has fully charged the battery will it stop charging at that point with no fear of over-charging..?

Sound feasible..?

Helmuth

[bdosborn]

This is an option too:
Unlike AGM batteries you can mix different age LiFePO4 batteries. If you decide you want more capacity in a year or so you can add another 40 a-hr battery in parallel to the one you have now.

Bruce
P.S. You might be able to tell from the blue that I really like Victron:

[cdnred]

This is an option too:
Unlike AGM batteries you can mix different age LiFePO4 batteries. If you decide you want more capacity in a year or so you can add another 40 a-hr battery in parallel to the one you have now.

Bruce

I see that you're in Littleton, CO. I worked for a few years in downtown Denver and lived in Littleton when I was there. The office I worked at closed up shortly after I left and the office got amalgamated into their other divisions. Beautiful city and surrounding area..

As you said, you can mix different aged LifePO4 batteries together but can you mix different ah batteries also..? Currently I've got a 40ah, can I add a 100ah down the road or must I get the same size as I have now 40ah..?

I'm thinking that the smart move for me is just to go with the Victron 20a DC-DC charger and keep the setup I have now..

Helmuth

[bdosborn]

As you said, you can mix different aged LifePO4 batteries together but can you mix different ah batteries also..? Currently I've got a 40ah, can I add a 100ah down the road or must I get the same size as I have now 40ah..?

Probably, lfhoward just added a 90a-hr to his existing 156 a-hr LiFePO4 cells:

https://www.tnttt.com/viewtopic.php?f=50&t=62581&start=1065
Scroll down about half way to see where he adds the new battery.

He's got lot of documentation in his posts on LiFePO4 batteries.
Bruce

[cdnred]

Been busy with my Xmas shopping, ahhh. From what I've been reading mixing different ah LifePO4 batteries together isn't an issue. Charging a LifePO4 is different from an AGM. My wiring harness is wired to charge while driving. So in my case with using a LifePO4 I'll need to put in a Victron 24/12 20ah DC-DC charger in line before connecting directing to the LifePO4 in order to recharge properly. Now down the road should I get the 100ah LifePO4 I should be able to just replace the 40ah with the 100ah and keep the same DC-DC 20ah charger as is. I decide on the 20ah DC-DC charger for minimal strain on the TV alternator. Going with the 30ah I think may be overkill for my TV alternator so the 20ah would be enough for my needs..

I only plan to use the DC on my TD for running my CPAP and recharge my cell phones. My CPAP DC Power Consumption is 12 VDC, 6.67 A so using a 12v 40ah LifePO4 battery how much run time would that give me..? If it's not enough then I'll give some thought into getting the 100ah now instead of later..

Both the 12v 40ah and 100ah batteries come with built in BMS and charger. Based on that I should leave them plugged in the whole time I'm plugged into shore power while camped or should it be put on a timer for say 6 hours to prevent over charging..?

I looked at picking the DC-DC charger up locally, just waiting for it to come in. Other then that I should be good to go..