DC to DC Charging

[traveldawg]

Surprisingly few threads specific to the topic of DC to DC chargers here, unless I just don't know how to use the search function. In any case, a couple of more specific questions:

1) When installing the wiring at the vehicle, most people appear to connect the wire to the battery rather than the alternator. I saw only one YouTube video where the person referenced that Victron prefers it be connected direct to the alternator rather than the battery. But that's the only time I heard that and can find no other information that references this method. Any thoughts on whether that would be better or worse than connecting at the battery?

2) When installing the ground wire at the vehicle I see most people run the ground wire (in tandem with the hot wire) from the battery to the back where they place a quick connect plug to go back to the camper. Is there any reason that one shouldn't just connect a short ground wire from the chassis at the rear of the vehicle to the quick connect plug rather than run from battery to rear?

Here is a link to my DC to DC install. (you can find most of my mods by searching "kalakamods" - without quotes).

Here is another link.

Another link.

I find these by opening a new browser tab and use google to search [mygrandrv.com "dc" "charger"] without the brackets but with the quotes.

My Renogy instructions said 4 gauge wire for the length I ran. Lots of discussion about running cable. I didn't use the truck frame as I found these aluminum Fords to have less than dependable chassis or body parts ground points.

oh - that terminal on the positive side of the driver's side battery is one I installed myself; it isn't on the Ford connector; I removed the connector, drilled a hole and used a bolt for the stud. I'm pretty sure that that battery is on the circuit side of the Ford BMS so battery charging remains under Ford's BMS control. I have dual alternators.

[Scott'n'Wendy]

Take serious good look at what you want to accomplish with your DC/DC. High amperage causes heat, causes failures. Don't try to pump more current than you really need to. Your truck will appreciate it.

[Riverbug]

Here is a link to my DC to DC install. (you can find most of my mods by searching "kalakamods" - without quotes).

Here is another link.

Another link.

I find these by opening a new browser tab and use google to search [mygrandrv.com "dc" "charger"] without the brackets but with the quotes.

My Renogy instructions said 4 gauge wire for the length I ran. Lots of discussion about running cable. I didn't use the truck frame as I found these aluminum Fords to have less than dependable chassis or body parts ground points.

oh - that terminal on the positive side of the driver's side battery is one I installed myself; it isn't on the Ford connector; I removed the connector, drilled a hole and used a bolt for the stud. I'm pretty sure that that battery is on the circuit side of the Ford BMS so battery charging remains under Ford's BMS control. I have dual alternators.

Thanks for that. I didn't see your threads when I searched for them in the forum. I'll try Google in the future. I upgraded the alternator when I ordered the truck because I was certain a DC charger would be the cat's meow. After all the comments about whether it's really necessary, I'm starting to wonder. I don't plan on solar. I have a Honda 2000i generator that I was thinking about mounting on the A frame. Perhaps I'll start with installing the Multiplus first, see how it works to charge with a generator as needed while overnighting consecutive days without shore power, and then decide how much a DC charge might improve the situation. But one question I have is about your comment on "exercising" your battery. I've always read that the main things you can do to extend the life of lithium batteries is don't charge them to 100%, don't deplete them below 20%, and the less charge cycles it goes through the longer it will last. Thoughts?

Edit: Just occurred to me that one main point about having the DC charger was so that I could run the fridge on AC while traveling (I will be installing a Multiplus) and not rely on propane. We travel 8 hours on average, then stop without shore power for consecutive days. I've got to think about this more...

[Butcher]

There are a lot of 'thoughts' about charging just about everything. If you only use 80-90% of the capacity of a lithium battery, then it will cycle longer. At some point, just the age of the battery will kill it. You can treat a battery so it can live 40 years, but in reality, they will fail sooner than that. Why? Because they are old.

Seems like there are two camps and both are certain they are right. What you need to do is research what the two camps are stating. Figure out what camp you would like to live in. Maybe, you want to live in the middle. There are some real valid points on both sides. I believe Will P has some good points on life cycles. One of his videos shows on paper, it could be the last battery you buy.

What works for me is a low voltage cut off of 2.7v. A high voltage cut off at 3.45. IF for whatever reason, I really am screwed, I can always change the BMS settings and go down to 2.5v. Kind of like a reserve tank.

I am a fan of bigger is better. More capacity is not really a bad thing. Start out small and anticipate that you will expand.

Some people get real upset if you do not agree with them. It's ok that you do not agree. Appreciate the differences. I still feel that it's odd that people get upset about that.

[Riverbug]

There are a lot of 'thoughts' about charging just about everything. If you only use 80-90% of the capacity of a lithium battery, then it will cycle longer. At some point, just the age of the battery will kill it. You can treat a battery so it can live 40 years, but in reality, they will fail sooner than that. Why? Because they are old.

Seems like there are two camps and both are certain they are right. What you need to do is research what the two camps are stating. Figure out what camp you would like to live in. Maybe, you want to live in the middle. There are some real valid points on both sides. I believe Will P has some good points on life cycles. One of his videos shows on paper, it could be the last battery you buy.

What works for me is a low voltage cut off of 2.7v. A high voltage cut off at 3.45. IF for whatever reason, I really am screwed, I can always change the BMS settings and go down to 2.5v. Kind of like a reserve tank.

I am a fan of bigger is better. More capacity is not really a bad thing. Start out small and anticipate that you will expand.

Some people get real upset if you do not agree with them. It's ok that you do not agree. Appreciate the differences. I still feel that it's odd that people get upset about that.

That's valid. I'm in the camp that if using 80%-90% of the battery will give me 5 years more in the life of the battery, I'm cool with that. I know people that seem to be happy replacing their lead acids every 2 or 3 years whereas mine go 6+ because I baby them. I'd prefer to do the same with my lithium. If I could get 12 or 15 years out of them by babying them, that would be fantastic! May be wishful thinking, but I'll give it a try.

[traveldawg]

Thanks for that. I didn't see your threads when I searched for them in the forum. I'll try Google in the future. I upgraded the alternator when I ordered the truck because I was certain a DC charger would be the cat's meow. After all the comments about whether it's really necessary, I'm starting to wonder. I don't plan on solar. I have a Honda 2000i generator that I was thinking about mounting on the A frame. Perhaps I'll start with installing the Multiplus first, see how it works to charge with a generator as needed while overnighting consecutive days without shore power, and then decide how much a DC charge might improve the situation. But one question I have is about your comment on "exercising" your battery. I've always read that the main things you can do to extend the life of lithium batteries is don't charge them to 100%, don't deplete them below 20%, and the less charge cycles it goes through the longer it will last. Thoughts?

Edit: Just occurred to me that one main point about having the DC charger was so that I could run the fridge on AC while traveling (I will be installing a Multiplus) and not rely on propane. We travel 8 hours on average, then stop without shore power for consecutive days. I've got to think about this more...

I am hardly the one to ask about battery plans, charging frequencies, levels, etc. I replace about 400ah of AGM with one 200ah Lithium and justified it for the weight savings. I just figure things work better when 'exercised' - kind of a use it or loose it mentality I guess. And I probably read someplace that using the battery is better than keeping it at full charge. For me I am still not sure I needed the DC to DC charger; still, I am glad to have it for the charge control on the battery when I do use it.

As it is I carry 2 Honda 2000's and am not shy about using them if necessary the dry camping. Usually once in the a.m. while having coffee & preparing for that day and again in the evening when appliance use is high again - all this assumes I am not running the ACs. I have no solar and doubt I will ever have it - I just don't need it.

I suppose if I were to do any amount of dry camping I would get a shunt and measure my power usage to determine the best way to manage the battery. Since you travel then dry camp for a while I think I would run the DC to DC charger while traveling since the batteries will get good use once stopped.

[Spike32]

Ok, this isn't specifically a solar question but seems the right place to post this question...

I picked up my new truck yesterday. I ordered the alternator upgrade to 397 amps; not sure if that is a single or dual alternator setup yet. I did the upgrade so that I could install a DC to DC charger. Two questions:

1) Using a clamp meter on the negative wires for each of the truck batteries (with all the accessories running) should give a good idea of what the truck's current draw is vs the remaining headroom available for driving a DC charger for the lithium batteries in the camper, correct?

2) If I want the DC charger to push about 40 amps to each of two lithium batteries in the camper (2 - 206AH SOK batteries), I would need an 80 amp DC charger, correct? (The batteries are rated for up to 50 amps charge input.)

Something tells me it won't be that simple but the first two questions on my list I am trying to answer is how much headroom I have with the truck alternator and how to correctly size the DC charger. Thanks.

F350 397 amp alternator option is 2 alternators. I have it on my 2021 7.3 F350.

[Boom 'r Bust]

Our 40A dc to dc charger is one of our best upgrades. And we are approaching $15k in diy upgrades...

Our 12cf fridge uses about 350 watts and the inverter about 40 watts. So the 500ish watts coming from my F350 7.3 gasser works perfectly. No problem arriving at our destination with 100% batteries. We have 420 ah of Lion lifePo.

[Riverbug]

F350 397 amp alternator option is 2 alternators. I have it on my 2021 7.3 F350.

Thanks, I since learned a bit more detail about it too. The primary alternator is apparently 250 amps which always runs and the second is 147 amps which only runs when load calls for it. I'm getting nuggets of information, eventually I'll have a complete knowledge pack.

[jjbbrewer]

The primary alternator is apparently 250 amps which always runs and the second is 147 amps which only runs when load calls for it.

That matches what I've read about the dual alternators on our trucks as well. I forget where I read it (maybe the ford-trucks.com forum?) but there's a control module that "calls for" the extra alternator to be energized, so I'm thinking that if you attach straight to the alternator, you might confuse/bypass that control module. So I read (again somewhere) that you should go straight to the battery (through a breaker of course) for these types of loads.

I installed dual Viair compressors that way and they're working great.