battery charging from tow vehicle

[Raspy]

Raz,
I'm sure you are right about the system being designed to not overtax the charging system. As an example, my F250 with a 397 amp alternator, (that's not a typo!), has #14 wires rated for about 15 amps going to the seven pin. That is a very safe margin! I always wonder if it is OK to upsize that wiring because it does not come from the battery, but from the computer, or computer controlled relay. I have no idea what can be sent through that system without damaging it. But I've never worried about the alternator.

[John in Santa Cruz]

Fwiw, my older F250 has a 40A fuse on the trailer charge circuit, but when I such around 24A out of it, I'm only seeing about 10V at the back of my Escape. My Victron Orion Tr 12/12-18 turns this into 18 amps at ~ 13.5-14.2 volts to charge my big lithium pack.

[Raspy]

Originally Posted by John in Santa Cruz

Fwiw, my older F250 has a 40A fuse on the trailer charge circuit, but when I such around 24A out of it, I'm only seeing about 10V at the back of my Escape. My Victron Orion Tr 12/12-18 turns this into 18 amps at ~ 13.5-14.2 volts to charge my big lithium pack.

John,
Sounds like you've found the perfect balance of available power and a dc-dc charger to work with it. I think you made a couple of typos, but I get what you mean. A reliable 18 amps of lithium charging without having to rewire the truck.

[Eggcentric]

Originally Posted by beardrum

As a temporary emergency measure, (while I puzzle thru the generator vs solar panel questions), would it be conceivable to pull the tow vehicle up close to the trailer battery, and charge it from the running car with jumper cables?

The jumper cables are much shorter and much bigger gauge wires than the charging circuit that goes thru the 7-pin connector. I've not had a lot of luck keeping the battery up to a full charge just from the tow vehicle's connection. I really don't want to run the battery down to anything close to fully discharged.

My relatively new and fully charged battery SHOULD be able to make it through three days of boondocking, but we'll be needing the furnace a bit, so it will get a workout. I'll be watching both the voltage levels and the remaining amp hour capacity.

Thanks for any comments!

Chuck

Another way to handle it is to put a switch on the truck battery, works like this, start the truck, let it run for a couple of minutes, then connect the trailer battery and open the switch on the truck batt,IN THAT ORDER. Now the alternator sees the battery that you want to charge, and will deliver all the power to it. You can pick up battery isolators (sold for anti theft) at auto parts stores.

[jeffminnesota]

Originally Posted by Raspy

My Oliver had no solar, and every time we camped without hookups, which was almost always, I charged it during our stay with jumper cables from the truck. This sends much more power to the batteries than the seven pin does, and as Alex mentioned, is quieter than a generator. I used a 2000 watt Yamaha generator too, but it was much more annoying and charged slower than the jumper cables. Eventually, I stopped bringing the generator on trips. The seven pin wiring is nearly useless for charging and in some trailers does not work at all.

The best way to charge from the truck is with an Anderson plug that has high amp wires directly from the tow battery to the rear bumper. Then the trailer plugs in there with its own set of wires running to its battery. This is as good as jumper cables, but can be used while driving too. It works fine for lead acid batteries, but if you switch to lithium, you need to add a dc-dc charger in the trailer to match the charging style of the truck to the lithium batteries in the trailer. The Anderson system is a fine addition to solar for when the weather is bad, or you just want to charge at night or while driving.

Question: This is intriguing, what gage wire would you use, and how long would it take to charge up a 75% trailer battery from a normal SUV alternator?

[Eggcentric]

PLEASE STOP WITH URBAN MYTHS, THEY ARE DANGEROUS.
Myth #1
Wire size is never ever ever used to limit power output, if there is more power passing through the wires than they can handle, they will overheat and may start a fire.
Urban myth #2,
Ir does not matter what source you use to charge lithium or lead acid batteries. What matters is that the charge rate (amperage) does not exceed the battery's ability to absorb the charge, (more critical with lithium) and that the voltage never exceeds the maximum that the cells can accept, again more critical with lithium.
If you try to charge faster than a lithium battery can absorb the power the cells will overheat and could ignite if the BMS has a thermister, it will shut the charging off if the temp of the batt gets too high, it will also not allow the battery if it is too cold . If you try to keep charging a lithium battery beyond it's voltage limit, the BMS will cut the power.

[Jim Park]

I purchased a Coleman solar panel, about 12"X 12" with a couple of large alligator style, clips. It's designed for charging auto and RV batteries and is not powerful enough to overcharge them. It was about $35 CAN. and keeps my trailer battery charged nicely, without monitoring. I did check the battery with an OHM meter regularly to be sure and the panel performed as advertised.

[CarlD]

Originally Posted by Eggcentric

PLEASE STOP WITH URBAN MYTHS, THEY ARE DANGEROUS.
Myth #1
Wire size is never ever ever used to limit power output, if there is more power passing through the wires than they can handle, they will overheat and may start a fire.
Urban myth #2,
Ir does not matter what source you use to charge lithium or lead acid batteries. What matters is that the charge rate (amperage) does not exceed the battery's ability to absorb the charge, (more critical with lithium) and that the voltage never exceeds the maximum that the cells can accept, again more critical with lithium.
If you try to charge faster than a lithium battery can absorb the power the cells will overheat and could ignite if the BMS has a thermister, it will shut the charging off if the temp of the batt gets too high, it will also not allow the battery if it is too cold . If you try to keep charging a lithium battery beyond it's voltage limit, the BMS will cut the power.

Regarding your myth #1 wire sizing can be used to limit the current to a load, and, it may not be by design, but, that is exactly what it does when your charging a trailer battery from a TV. However the fuse that feeds that circuit must be properly sized to protect the wire. Not really relevant here, but the current limiting capabilities of a wire is used when calculating the SCCR (Short Circuit Current Rating) of loads in AC circuits.

Urban myth $3. Overtemp protection is pretty much standard on all LFP batteries, however undertemp protection is not, you have to read the specs. Battleborn, pretty much the industry benchmark, has it, a $375 Chins does not.
You can live without undertemp protection and it can sometimes be implemented by the charger with proper design.

Regarding emergency charging. I use a 1000 watt inverter, that I connect to the tv battery and just plug the trailer into it. I just run the truck and let the trailer 45 amp LFP charger do its thing. It is a lot smaller that a generator, I don't have to carry a gas can and it requires no maintenance. And if I need AC for something, like cutting my whiskers, it comes in handy.

[100mpg]

Originally Posted by Gene680

My Ridgeline has a tow package which includes a larger alternator. Would this provide enough boost to charge the Casita house battery while driving?

My ridgeline has never had a problem keeping the OEM battery in the 17' Casita FD charged up throughthe 7 pin. It is a so called "Deep cycle" (not really) lead acid battery. It is at the end of its life (7years old) and it still charges up from my truck. It doesn't last that long but it still charges!

[EllPea in CA]

Originally Posted by CarlD

…Regarding emergency charging. I use a 1000 watt inverter, that I connect to the tv battery and just plug the trailer into it. I just run the truck and let the trailer 45 amp LFP charger do its thing. It is a lot smaller that a generator, I don't have to carry a gas can and it requires no maintenance. And if I need AC for something, like cutting my whiskers, it comes in handy.

VERY INTERESTING! I am only interested in using AC very briefly for my one civilized indulgence, the coffee maker. I have done the math, and the draw is 15 Amps. I understand the small inverter I have would not handle the coffee maker. What advice do you give me? Do I actually need a 1000 watt Inverter to accomplish this? And I definitely am not interested in buying or running a generator just to make coffee. But I would consider starting up my tow vehicle briefly to do so!

[100mpg]

Originally Posted by EllPea in CA

VERY INTERESTING! I am only interested in using AC very briefly for my one civilized indulgence, the coffee maker. I have done the math, and the draw is 15 Amps. I understand the small inverter I have would not handle the coffee maker. What advice do you give me? Do I actually need a 1000 watt Inverter to accomplish this? And I definitely am not interested in buying or running a generator just to make coffee. But I would consider starting up my tow vehicle briefly to do so!

most drip coffee makers ate over 1000 watts, right about 14-1500. You could boil water on the stove and pour it into coffee filter holder and do it the old fashioned way!

[AlanKilian]

Originally Posted by EllPea in CA

I have done the math, and the draw is 15 Amps.

Do I actually need a 1000 watt Inverter to accomplish this?

A 120 Volt AC coffee maker drawing 15 Amps is 120*15=1,800 Watts.

So, your 1,000 Watt inverter isn't going to cut it.

Now, you said you did the math, but 15 Amps for a coffee maker seems high.

I looked at a Mr. Coffee and it says 900 Watts, but our fancy-schmanch Technivorm says 1,400 Watts, so maybe they do take that much.

The one we have takes none.
https://photos.google.com/search/cof...gwb2IAPfQgi-6l

[EllPea in CA]

Originally Posted by AlanKilian

A 120 Volt AC coffee maker drawing 15 Amps is 120*15=1,800 Watts.

So, your 1,000 Watt inverter isn't going to cut it.

Now, you said you did the math, but 15 Amps for a coffee maker seems high.

I looked at a Mr. Coffee and it says 900 Watts, but our fancy-schmanch Technivorm says 1,400 Watts, so maybe they do take that much.

The one we have takes none.
https://photos.google.com/search/cof...gwb2IAPfQgi-6l

Well, I got a flashlight out and looked closer. It says 60 Hz and dang it, 1520 W. I only saw the hertz and did a Google conversion which indicated 15 Amps. I see what you’re saying about heating the water up, yada yada, which is what I have done for years.

I was just really, really, hoping to just have this one indulgence, which is the Keurig coffee maker… just 12 ounces, heat it up really fast for various purposes including coffee. So much quicker and easier than lighting the stove and boiling the water and pouring it over and cleaning up.

I’ll ask you here, since you did not reply on another thread… After all of your lovely conversions in your 13 footer, you posted that you camp in a tent? Inquiring minds want clarification!

[Travellers]

Hi folks. Woohoo. First contribution to the forum.

We built (or more assembled) a 10 amp DC to DC converter so the tow vehicle would charge the trailer battery at a better charge voltage. So 14.4 instead of 12.1 or whatever voltage was on the end of the charge line from the tow vehicle. The voltage drop is significant. The current is a little less but the voltage (or pressure) is a more appropriate voltage. We got a couple of meters off of amazon so we could see the voltage coming in and going out. We mounted it all in a little craftsman toolbox and it goes nicely in a cubby close to the AGM batteries (which is under the bed).

Anyway, just an idea. I'm a tinkerer so it was a fun little project. We like short travel days but even after a couple or three hours we are able to restore a reasonable amount to the 2 X 6 volt AGM's.

Here is a pic or two. It's on the bench here but tow vehicle 12 volts comes in the left, corrected charge voltage headed for the 2 X 6 volt AGM.s heads out the right.





Safe travels all.

[Raspy]

Originally Posted by EllPea in CA

Well, I got a flashlight out and looked closer. It says 60 Hz and dang it, 1520 W. I only saw the hertz and did a Google conversion which indicated 15 Amps. I see what you’re saying about heating the water up, yada yada, which is what I have done for years.

I was just really, really, hoping to just have this one indulgence, which is the Keurig coffee maker… just 12 ounces, heat it up really fast for various purposes including coffee. So much quicker and easier than lighting the stove and boiling the water and pouring it over and cleaning up.

I’ll ask you here, since you did not reply on another thread… After all of your lovely conversions in your 13 footer, you posted that you camp in a tent? Inquiring minds want clarification!

When camping, I make electric coffee every morning with my Mr. Coffee 5 cup coffee maker. It draws 650 watts for about six minutes to make the coffee. You can hot rod it to get a couple extra cups out of it for a little longer power draw. And the "keep warm" cycle is optional. About 9 bux at Walmart.

[Raspy]

Originally Posted by jeffminnesota

Question: This is intriguing, what gage wire would you use, and how long would it take to charge up a 75% trailer battery from a normal SUV alternator?

The first one I did was on my Ram 3500. I ran #6 stranded wire from the starting battery to the rear bumper, installed an Anderson plug there, and used the factory #6 wiring in the trailer that went directly to the house batteries. #6 all the way.

The second one I did I used #4 marine Romex in the truck and #6 stranded in the trailer.

The first system supplied 24 - 50 amps. The first one worked very well on AGM batteries wired directly. The second one worked on Lithiums, but was not the proper setup for lithiums and I only used it under certain circumstances. Enough to assure it worked, then went to a 30 amp dc-dc charger to properly charge the lithiums. With the dc-dc charger it happily supplies 30 amps to the batteries.

I cannot estimate how long it would take to charge your battery as I have no idea what size it is, etc.

[CarlD]

Originally Posted by EllPea in CA

VERY INTERESTING! I am only interested in using AC very briefly for my one civilized indulgence, the coffee maker. I have done the math, and the draw is 15 Amps. I understand the small inverter I have would not handle the coffee maker. What advice do you give me? Do I actually need a 1000 watt Inverter to accomplish this? And I definitely am not interested in buying or running a generator just to make coffee. But I would consider starting up my tow vehicle briefly to do so!

My electrical power needs are not as great as yours. You would need a larger inverter, 1500-2000 watts or so. When you get into these power levels wiring and good connections are a must. 1500 watts at 120 volts will draw 12.5 amps. That amount of power at 12 volts will draw 125 amps divided by .85 efficiency is 150 amps. You need some serious wire and good connections. I would boil water on my propane stove and make drip coffee as others have suggested. I think it would be easier to find different indulgence, like maybe a lava lamp!

[Raz]

You would need a larger inverter, 1500-2000 watts or so. When you get into these power levels wiring and good connections are a must. 1500 watts at 120 volts will draw 12.5 amps. That amount of power at 12 volts will draw 125 amps divided by .85 efficiency is 150 amps. You need some serious wire and good connections. I would boil water on my propane stove and make drip coffee as others have suggested

Yup. Inverter, wire, and the cost to have it installed. $$$$$

OXO makes a very nice pour over for less than $20. I like it so much I use one at home.

[John in Santa Cruz]

a 1800 or 2000 watt inverter requires 2/0 AWG wire for the DC side. 2/0 has a conductor diameter of 0.43 inches, and weighs about 0.5 lbs per foot. This should be fused at 200 amps.

I wired my big LFP batteries with AWG 4 to the ANL fuses (100A per battery) and from the fuses to the bus bars. if I want to add a 1800W inverter, I will need to redo that with 2/0

all this so my wife can run her hair dryer

[CarlD]

Your wife must have an "industrial strength hair dryer and she can't live without it".