DC to DC Charging

[Riverbug]

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.

That's a really good point. I guess it would make sense to attach to the battery to ensure both alternators get engaged when needed. And looking at the engine bay, it would certainly be an easier install.

[Scott'n'Wendy]

@Riverbug
Does the second alt have a clutch on it something like on the A/C compressor? Or is it a relay on the O/P?

400 amps from the engine bay. Amazing. Pretty soon there are going to be hook up kits to connect a truck to your house so in power failures you can keep the lights and fridge running..lol
My Challenger from the 70's came stock with a 37 amp alt.

[Riverbug]

I guess it's a sensor relay. There is no clutch. I'm not sure how much the second one would really get used even with a DC charger, but it's there if it's needed and it's just an added expense if it isn't needed.

[traveldawg]

I'm not so sure about that business of the second alternator only operating when called on for extra amps. Over on the Ford Truck forum there is a discussion I am involved in. Someone posted the Ford schematic/diagram of how the alternators connect. It looks to me like both operate simultaneously. Their output is controlled via the PCM so maybe it can regulate the current as well as the voltage from each alternators regulator - I am not sure and haven't found any concrete information explaining the function.

I'm still interested in the BMS and where it is and how it functions.

I monitor the alternator voltage via Forscan and both are up in the 14.0 VDC range all the time; one is always a volt or a bit more than the other.

bottom line for me: I think they both operate all the time feeding both batteries simultaneously. But I'm open to references to how they actually work.

[SolarPoweredRV]

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...

Here is a note about charging Lithium batteries...

What you said about charging Lithium batteries is true, however, this applies to "Lithium Ion" batteries. What you have are "Lithium Iron Phosphate" batteries (LiFePo4). LiFePo4 batteries are a different chemistry and they like to be charged to 100%, however, with an expected longevity of 4,000 cycles or more, I don't think you should be too concerned about either keeping them fully charged, or draining them too much. Your BMS will keep your batteries healthy. So, use them how you like.

Running your Fridge on A/C would draw almost as much energy as traveling with your Air Conditioner running. Your fridge uses resistive heat when it is operating on A/C power and Resistive Heat uses a whole, WHOLE, LOT of Electrons. It would be okay to run your fridge on A/C if you are going through a tunnel, or are on a Ferry, but otherwise your two SOK batteries are probably going to be drained when you arrive at your destination.

One thing you haven't addressed, is how much work 80 amps are going to be placing on your Alternator. You might just burn out your Alternator because you will be placing a constant 80 amp load on it for 8 hours. Your Alternator is not designed for that much load for that many hours straight.

You may have noticed that I spoke about your Alternator as though you only have a single Alternator versus your Dual Alternator setup. This is because Ford does not share the Alternator load evenly between the two Alternators. Because of fuel economy, the second Alternator rarely gets used. Ford only wants to use that Second Alternator as a last resort.

For a detailed look into how Ford utilizes their dual Alternator system, and how charging Lithium (LiFePo4) via a DC - DC Charger works watch the following Video from YouTuber "Mortons on the Move"...

https://www.youtube.com/watch?v=uwrG3gUdDT8

[SolarPoweredRV]

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.

You don't need to "Baby" your Lithium batteries. The BMS is designed to protect the batteries. LiFePo4 batteries are rated at greater than 4,000 cycles and a cycle is defined as 100% SOC to 0% SOC. If you are draining your batteries every day, >4000 cycles will give you 11 years of service and each day you only draw down to 30% (+/-) is a day that does not count against that (greater than) 4,000 number. I am not advocating you abuse your batteries, I'm just suggesting that your batteries may last longer than your camper.

[SolarPoweredRV]

@Riverbug
Does the second alt have a clutch on it something like on the A/C compressor? Or is it a relay on the O/P?

400 amps from the engine bay. Amazing. Pretty soon there are going to be hook up kits to connect a truck to your house so in power failures you can keep the lights and fridge running..lol
My Challenger from the 70's came stock with a 37 amp alt.

Pretty soon there are going to be hook up kits to connect a truck to your house so in power failures you can keep the lights and fridge running

There already is, it's called the Ford Lightning!

It can run your house for a couple of days.

I test drove it, AWESOME Truck !!!!!!!!!!!!!!!!!

Simply AMAZING !!!!!!!

[SolarPoweredRV]

I'm not so sure about that business of the second alternator only operating when called on for extra amps. Over on the Ford Truck forum there is a discussion I am involved in. Someone posted the Ford schematic/diagram of how the alternators connect. It looks to me like both operate simultaneously. Their output is controlled via the PCM so maybe it can regulate the current as well as the voltage from each alternators regulator - I am not sure and haven't found any concrete information explaining the function.

I'm still interested in the BMS and where it is and how it functions.

I monitor the alternator voltage via Forscan and both are up in the 14.0 VDC range all the time; one is always a volt or a bit more than the other.

bottom line for me: I think they both operate all the time feeding both batteries simultaneously. But I'm open to references to how they actually work.

Check out this Video by Tom Morton from "Mortons on the Move" YouTube channel. He goes into detail how Ford controls the second Alternator and how he used DC-DC charging on his truck.

https://www.youtube.com/watch?v=uwrG3gUdDT8

[SolarPoweredRV]

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.

What you are wanting to do, power your camper with 80 amps continuously, will probably lead to premature Alternator Failure. Accomplishing 80 amps of continuous charging power is better done with a special High Output Alternator, these alternators are often used on boats with high electrical demands. I do believe they are available for vehicles if you wanted to go that route.

However, I would recommend you re-examine your requirements...

First, you only have two batteries for a total of 400ah.

Second, you are looking at 80 amps for 8 hours That's 640ah, that is much more charging than you need.

Realistically, how often are you going to start your driving day with 0% SOC? You already said you usually start your Generator every morning so your Converter (or Inverter/Charger) will be adding power to your batteries all the time it is running (i.e.: 100 amps charging for 1 hour yields 25% SOC added to your batteries).

If you had a 12v DC fridge (or a residential fridge) I would say you could probably run your fridge from the truck via the DC-DC converter, however, since you have the Propane/ AC fridge, I don't think your battery bank and/or Alternator is large enough to handle that amount of draw.

Let's take a look at what you seem to be wanting to accomplish:

By eliminating running the fridge on A/C, you now have more moderate energy usage requirements.

You want to stop overnight, fix your dinner and maybe use the entertainment center for a bit before going to bed, you also want to be able to keep the coach warm overnight if it is cold (reminder: the Furnace is an energy pig). You have 400ah of battery storage and you started your trip with 100% SOC in your batteries. With DC-DC charging from the truck, you should arrive with ~100% SOC on the first night. Even if you have a cold night you should not use more than 200ah (50%) of your batteries. Depending on whether you run the Generator in the morning, you will begin your Travel day with more than 50% SOC.

Based on the above scenario, I would recommend you get a 30 amp DC-DC Converter. This would most likely give you a full charge by the time you stop every night (30 amp x 8 hours yields ~ 240ah). a 30 amp DC-DC Converter would be much less stress on your Alternator(s) and your wiring would be much smaller and cheaper.

If you find that the 30 amp DC-DC Converter is not enough, I would recommend expanding your battery bank so any short fall in your daily charging could be buffered by the larger battery bank (and occasional Generator use). I experienced a daily shortfall of about 10% on my return trip from Phoenix to Tampa. Because the Sun was low in the sky, (Winter) my Solar was unable to keep up with our daily usage, however, because our battery bank was so large, I was never concerned because eventually, we would stop at a campground and charge up the batteries (or hookup the Generator).

[Boom 'r Bust]

Here is a note about charging Lithium batteries...


Running your Fridge on A/C would draw almost as much energy as traveling with your Air Conditioner running. Your fridge uses resistive heat when it is operating on A/C power and Resistive Heat uses a whole, WHOLE, LOT of Electrons. It would be okay to run your fridge on A/C if you are going through a tunnel, or are on a Ferry, but otherwise your two SOK batteries are probably going to be drained when you arrive at your destination.


https://www.youtube.com/watch?v=uwrG3gUdDT8

David,

I agree with almost all of your points in the previous several posts. But the one about the frig using as much power as an air conditioner?

My 12cf frig uses 360ish watts on AC power. My air conditioning uses 1200 to 1600 watts depending on which one I'm running. My 40A DC to DC charger is a perfect match for running the frig on AC while driving.

Not sure what you are basing that opinion on...

Boomer