Charging while towing
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Forum Name: Miscellaneous / Off-topic
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URL: http://www.rpod-owners.com/forum_posts.asp?TID=14159
Printed Date: 30 Apr 2024 at 5:17am
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Topic: Charging while towing
Posted By: pedwards2932
Subject: Charging while towing
Date Posted: 25 Oct 2020 at 8:20am
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Not sure if this would work but I was thinking of a way to avoid trying to run really large wiring from vehicle battery to TT. You can get 300 watt inverters fairly cheap that will run off a cigerette lighter outlet. The NOCO GENIUS10 puts out 10 amps and requires 150 watts. Seems like this may be enough to keep the battery charged while towing. I know you can get dc to dc chargers but they require you run really large wires. What do you think?
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Replies:
Posted By: StephenH
Date Posted: 25 Oct 2020 at 9:07am
I'm unsure of your question. I ran wires to run a DC to DC charger for an LiFePO4 battery. If you are only running Pb-Acid, you may not need to do anything if your tow vehicle already has sufficient wiring to charge it. If your tow vehicle's wiring for charging is at least 10 AWG, you should be okay. Otherwise, run the wire. Running an inverter and then a charger would add significant efficiency losses. Since your TV should be able to charge the battery, why add these in? Now if it is for a DC to DC charger because you installed an LiFePO4 battery, it is a different matter. The TV won't charge it properly and you need to run the charger. See my mods for what I did.
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StephenH
Happy is the man that findeth wisdom,...
http://www.rpod-owners.com/forum_posts.asp?TID=7712 - ouR escaPOD mods
Former RPod 179
Current Cherokee Grey Wolf 24 JS
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Posted By: pedwards2932
Date Posted: 25 Oct 2020 at 9:25am
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The LifePo's are a bit expensive for my budget. The TV will only charge based on the starter battery so it doesn't charge much more than 80%. The Ford Escape is very difficult to run wiring and I just had it wired for the trailer and they used 12 gauge so I would have to pay to get them to run larger wire. The DC to DC wiring would require large wire as well. I like to run my refrig on 12 volt while towing which adds about a 6 amp draw so on a long haul the battery would be down pretty good if I do a pull off stop with no hook up. Just thought this would be a cheap way to boost the charging circuit.
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Posted By: offgrid
Date Posted: 25 Oct 2020 at 10:14am
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Not sure I understand, are proposing to install a 300watt inverter in the Escape, then run an ac line to the trailer, and connect it to the existing WFCO charger? Or to a separate charger maybe? Some other configuration?
You would be fighting basic physics the whole way, because each of those devices is only about 80-85% efficient. So that's an overall efficiency of about 60-70%. The rest is lost to heat. And you would need to run a new set of conductors for the ac circuit anyway. IIRC, the fridge takes about 11-12 A on DC, so you would need to supply the inverter with 12/0.6 = 20A or so to make up for the losses. That will just put more load on your TV charging circuit. Like everything in the real world, TANF (there ain't no free lunch) applies.
IIRC, the fridge in DC mode consumes about 11-12A. So, while its unfortunate that they ran 12 awg wire, it has adequate ampacity for the application. You will lose about 1 volt to wire resistance. So you're right that you won't be able to maintain full charge on your trailer battery.
I suppose you could add a dc/dc boost converter on the 12V line, that would be better than an inverter plus battery charger. Or, How about just running the fridge on propane?
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
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Posted By: pedwards2932
Date Posted: 25 Oct 2020 at 10:45am
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No I was saying use the inverter to supply AC to the 10 amp NOCO GENIUS10 that requires 150 watts so you could use a 300 watt inverter. Noco puts out 10 amps of charge to battery and rolls back to 3 when charged. So I would clip it to the trailer battery and plug it into the inverter hooked up to the vehicle 12 volt. Not sure the 85% efficiency would apply. My thought is between the alternator and the charger that would keep the charge up. The refrig doesn't run constantly does it? I could be wrong I am just thinking outside the box.
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Posted By: mcarter
Date Posted: 25 Oct 2020 at 10:50am
They do make battery to battery charging systems that feed off the tow vehicle, charge a remote battery(RV/boat/etc). They do not interfere with the vehicle battery charge. Google "battery to battery charge" or "charging a remote battery". A lot of big motorhomes and RVs have them. They are not cheap at least for good systems. It also may give you ideas with your proposed solution. The problem with most vehicle systems is they are designed to take care of the vehicle battery. They monitor and provide based upon vehicle need, not a remote battery. If I travel with reefer on DC my TT battery will be somewhat discharged upon arrival and that is with a 12V battery source thru the 7 pin. If you really want to charge a remote battery with a vehicle system, you need to look at battery to battery systems that isolate your vehicle charge and have proper components to charge a trailer battery.
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Mike Carter
2015 178
" I had the right to remain silent, I just didn't have the ability."
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Posted By: pedwards2932
Date Posted: 25 Oct 2020 at 11:10am
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The charger looked like a pretty full featured charger and fairly small so it would be easy to mount at the battery. Here is the link https://no.co/genius10 By specs it takes 150 watts to run it which is a pretty small inverter (300 watt) I looked at DC to DC chargers and again ther require large wire to implement.....the inverter would not. I may try it just to see if it will work....at worst i would end up with an 300 watt inverter and a nice charger.
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Posted By: offgrid
Date Posted: 25 Oct 2020 at 12:00pm
Originally posted by pedwards2932
No I was saying use the inverter to supply AC to the 10 amp NOCO GENIUS10 that requires 150 watts so you could use a 300 watt inverter. Noco puts out 10 amps of charge to battery and rolls back to 3 when charged. So I would clip it to the trailer battery and plug it into the inverter hooked up to the vehicle 12 volt. Not sure the 85% efficiency would apply. My thought is between the alternator and the charger that would keep the charge up. The refrig doesn't run constantly does it? I could be wrong I am just thinking outside the box. |
Yes the 11-12A 12V fridge current is continuous. And yes two 80-85% efficiency multipliers would apply. How could they not, you are taking your TV alternator/12V battery output through the inverter and then through the battery charger.
Where are you planning to connect the inverter to the TV 12V supply? You would be doing this while stopped using a temporary connection? If so just use propane. If you are doing this while driving you would need to run a separate 120V line between the inverter ac output and the battery charger. Better to just run a heavier 12v dc line.
Or are you thinking to mount the inverter in the trailer and connect it to the 12V supply from the TV there? If you do that you will have even more voltage drop in the 12V feed from the TV, because of the efficiency losses. You would also have to disconnect the 12V feed from the trailer battery, or you would be trying to charge the trailer battery from itself, losing energy in the process. That would be a form of perpetual motion.
Like I said, TANF.
I do think a dc/dc converter would work. You would have one efficiency loss (dc/dc's are around 90%), which the 12avg wire could handle and still supply 12A to the fridge. The dc/dc would boost the supply voltage from the TV battery/alternator which would compensate for the voltage drop in the 12awg wire. You would disconnect the 12V TV supply to the trailer battery and run it through the dc/dc instead, just like StephenH has done with his Li battery installation.
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
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Posted By: pedwards2932
Date Posted: 25 Oct 2020 at 1:10pm
I must not be explaining this very well. Inverter is powered by vehicle battery thru a cigarette lighter plug. Charger plugs into inverter. Charger connected to trailer battery. I would run the AC cord from inverter thru back door. This would be temporary setup to see how it works. I am not sure how you are getting the inefficiency as I know the inverter is not efficient but if it supplies 300 watts at 120 volts the charger should be as efficient as if it were plugged into a house outlet?I didn't realize the refrig draws constantly I thought with the thermostat it would shut on and off.
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Posted By: offgrid
Date Posted: 25 Oct 2020 at 3:37pm
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Ok, I think I get it now.
Ultimately you would need to run a permanent 120Vac line to the trailer. So, if that is the plan, why not just run a heavier gauge 12Vdc line now and be done with it? 10 gauge is what I and I think most of us have and that works fine to run the fridge while on the road. The voltage drop from that is only about 0.5V at 12A. Since you already have 12 awg running you could also just add a second 12awg conductor in parallel with the one you have and that would even be a little better than one 10 gauge.
The absorption fridges require a continuous heat source so the 12Vdc element just stays on all the time.
Re efficiency, if you run straight dc from the TV battery to the trailer battery, the only loss is the voltage drop in the wire. If you proivide energy via an inverter and charger then the losses would be the voltage drop from the TV battery to the inverter (significant), the efficiency loss in the inverter converting 12Vdc to 120Vac (about 0.85), drop in the ac cable to the trailer from the inverter (insignificant), the efficiency loss in the charger converting 120Vac back to 12Vdc (about 0.85), and the wire loss between the charger and the trailer battery. You will wind up needing about 20A out of your alternator/TV battery to get 12A to the fridge. Also, you will end up with no current flowing through the existing 12awg dc circuit because the charger would be trying to maintain the trailer battery at a higher voltage so current would not end up flowing through the 12awg connector.
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
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Posted By: pedwards2932
Date Posted: 25 Oct 2020 at 3:43pm
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Running a large wire on the Escape would be impossible for me, you have to jack the car up so I would have to take it in and pay to have it done....about $150.
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Posted By: offgrid
Date Posted: 25 Oct 2020 at 4:18pm
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Ok, but you would have the same issue running a new 120Vac line, right? Plus that would need a mounted 120Vac rated receptacle in addition to your 7 way connector. And you'd need to work up a locking system for the plug running from that receptacle to the charger so it didn't fall out on the road.
I really think that if you don't want to run a larger conductor you would be better off with a dc/dc converter. Simpler and more efficient, and you can use your existing 12awg line for it. Run that to the dc/dc mounted in the trailer and from there to the trailer battery. You might try something like this and see it it works for you:
https://www.amazon.com/Voltage-Converter-DROK-Regulator-Transformer/dp/B076TTBKFG/ref=pd_sim_23_1/134-4078344-2225341?_encoding=UTF8&pd_rd_i=B076TTBKFG&pd_rd_r=90d715bf-9599-481e-8516-74f3ce46b730&pd_rd_w=Cfd0R&pd_rd_wg=26qNS&pf_rd_p=d338b989-51db-4d99-9bd8-988f67d205eb&pf_rd_r=DZV3M8YQFTBRYQ8HBVJV&psc=1&refRID=DZV3M8YQFTBRYQ8HBVJV - https://www.amazon.com/Voltage-Converter-DROK-Regulator-Transformer/dp/B076TTBKFG/ref=pd_sim_23_1/134-4078344-2225341?_encoding=UTF8&pd_rd_i=B076TTBKFG&pd_rd_r=90d715bf-9599-481e-8516-74f3ce46b730&pd_rd_w=Cfd0R&pd_rd_wg=26qNS&pf_rd_p=d338b989-51db-4d99-9bd8-988f67d205eb&pf_rd_r=DZV3M8YQFTBRYQ8HBVJV&psc=1&refRID=DZV3M8YQFTBRYQ8HBVJV
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
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Posted By: StephenH
Date Posted: 25 Oct 2020 at 4:19pm
This is still counter productive. Why not just run on propane while not connected to shore power. That is what I have done until I recently completed the DC to DC charger for the LiFePO4 battery. I also had a problem with charging while the refrigerator was on 12V power. We ran with propane for 4 years with no issues.
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StephenH
Happy is the man that findeth wisdom,...
http://www.rpod-owners.com/forum_posts.asp?TID=7712 - ouR escaPOD mods
Former RPod 179
Current Cherokee Grey Wolf 24 JS
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Posted By: offgrid
Date Posted: 25 Oct 2020 at 4:34pm
Originally posted by StephenH
This is still counter productive. Why not just run on propane while not connected to shore power. That is what I have done until I recently completed the DC to DC charger for the LiFePO4 battery. I also had a problem with charging while the refrigerator was on 12V power. We ran with propane for 4 years with no issues.
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+1, I already suggested that. Consider that 12V operation isn't even an option on the new rPods with the larger fridges, either your fridge is off while towing or you run on propane. Some folks just aren't comfortable with the propane on while towing I guess.
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
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Posted By: pedwards2932
Date Posted: 18 Dec 2020 at 4:46pm
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I have my pod in storage and needed to charge the battery. I hooked my inverter to my Escapes 12v plug and used a charger I had. It is a 10 amp charger and it draws 1.9 amps. It worked perfectly so I suspect if I wanted to run a charger while underway I could do it easily with no additional wiring. Not sure how much draw the inverter uses running the charger but it is not an issue when engine is running.
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Posted By: offgrid
Date Posted: 18 Dec 2020 at 9:46pm
How do you get power to the rpod without additional wiring? There have to be some current carrying conductors there one way or another. Either you will be using the existing 12V conductors, running new 120V ones, or running new 12V ones.
Re efficiency losses, you are probably charging at about 14V so that is 14x10=140 Watts. You are providing the charger with 120v x 1.9A=228 watts, so you have lost close to 40% of the power in the charger alone. You will likely have a comparable loss in the inverter, so you will wind up requiring something like 20A or more from your alternator to get 10A (btw the fridge takes about 11-12A at 12V).
So why not just run the fridge on propane and for everything else directly charge from the alternator as per normal practice? I don’t see the upside?
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
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Posted By: pedwards2932
Date Posted: 19 Dec 2020 at 7:50am
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"From a legal standpoint, so long as your propane lines and the RV refrigerator are installed according to code, then there is no law against driving down the road with the propane system on. However, there is one caveat to keep in mind. Most states require you to turn off all gas appliances and sources of flame when you are refueling."
I'm not thrilled with turning off and on the propane everytime I fuel. I have been able to run with the frig on DC for 9 hours with no issue while driving. The charger idea is more for if I want to do an overnight and don't have a AC hookup....I can top off the battery when I park. My Escape is already wired for 12 v in the rear of the car so it is just a matter of plugging in the converter and connecting to the battery.
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Posted By: pedwards2932
Date Posted: 19 Dec 2020 at 8:04am
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Also the 1.9 amps is max draw on charger.....it doesn't charge at max very lon at all. If it were coupled with the alternator output of the car I doubt it would pull full charge either as the alternator would assist. I don't intend to use it on the road since the alternator seems to keep up okay. My next purchase is digital voltmeter so I have a better idea what is going on with the battery. Found a pretty cool one that will plug into my 12 v port on the pod.
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Posted By: Olddawgsrule
Date Posted: 19 Dec 2020 at 8:04am
Originally posted by pedwards2932
Not sure if this would work but I was thinking of a way to avoid trying to run really large wiring from vehicle battery to TT. You can get 300 watt inverters fairly cheap that will run off a cigerette lighter outlet. The NOCO GENIUS10 puts out 10 amps and requires 150 watts. Seems like this may be enough to keep the battery charged while towing. I know you can get dc to dc chargers but they require you run really large wires. What do you think? |
Since the Rpod's converter already has the capability of charging the battery while the vehicle is running, I have to assume your TV does not have a strong enough alternator to run it. The other option, as you are trying to do, is to use a smaller charger in hopes of it working.
There is a Auto-breaker up front on the Rpod and this is where I tapped in to run my inverter. Just follow the wiring back on the harness, you'll see it. This may be your spot to tie in.
Like others, I do believe you are better served not going DC/AC/DC and staying DC/DC. Pickup a smaller DC/DC unit that doesn't require as much input wattage.
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https://www.youtube.com/channel/UCJduGeZNFgtptH67leItRFQ - Byways no Highways
2017 Tacoma
http://tnttt.com/viewtopic.php?f=55&t=72408 - Truck Camper Build
2004 F150 My Overlander
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Posted By: pedwards2932
Date Posted: 19 Dec 2020 at 8:35am
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My car was already wired for the DC and I already had the inverter to run my TV on DC when needed. As I said so far running the refrig on DC hasn't caused an issue in 9 hours I probably don't need it while running but if I am stopping for overnight without a hook up it would help to top off the charge. I wasn't aware of the converter charging the battery while running.....I assumed the alternator output was charging the pod battery?
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Posted By: offgrid
Date Posted: 19 Dec 2020 at 9:24am
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OK, now I'm totally confused about what you are trying to accomplish. I thought it was to increase charging current while towing so you cam run the fridge on 12v? But you are saying that's not a problem. There is some kind of basic misunderstanding here I think.
Lets try it this way. Think in terms of energy flows. When you say you want to "top off" the trailer battery once you've parked, where is that energy coming from? Are you idling your tow vehicle and using the alternator to provide it? If so, just change the fridge over to propane and leave the 7 way connector attached. Problem solved.
You can't charge from the tow vehicle without the alt running because that will remove energy from the TV battery and discharge it in short order. If you are thinking that you can charge directly between the two batteries using the 7 way while at the same time charging via an inverter/charger in parallel that won't happen. The dc voltage will be established by the two batteries which are after all connected in parallel forming a single 12V buss. The inverter/charger will just act like a load, basically a high tech heater sucking more energy from the system than its putting back in to the same buss its drawing from. You would have to disconnect the 12V connection between the two batteries and charge only through the inverter/charger. But why do that if you can charge directly far more efficiently just like you are doing while driving?
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
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Posted By: pedwards2932
Date Posted: 19 Dec 2020 at 9:45am
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I am charging with the alternator while driving. If I arrive at a campground with a hook up nothing is needed but to hook up. If I am doing an overnite with no hookup I can use the charger if needed. I don't see the complication.....this avoids needing a generator or solar panels. When I did it yesterday it charged very quickly so the battery didn't need a lot of charge. I can monitor the Escapes battery to see when it would need to be started......I honestly don't see the complication.....very similar to using a generator to charge up the battery.
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Posted By: offgrid
Date Posted: 19 Dec 2020 at 10:11am
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When you use a generator you are providing an external energy source. Ditto when you run the engine to use the alternator. Ditto again if you charge from a solar module.
But if you attempt to charge the trailer battery from the tow vehicle battery you are merely moving energy from one battery to the other. It is a zero sum game, so completely different from using an external source. And the battery you are removing energy from has less capacity than the one you are moving it to.
And if you use an inverter/charger you are moving it in a way that wastes about half of what you are moving. Its counter productive. If you want to be able to run the trailer from both batteries just leave the 7 way connected and that will happen without any waste. Just be careful not to run both batteries down and not be able to start the TV.
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
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Posted By: pedwards2932
Date Posted: 19 Dec 2020 at 10:24am
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Ok lets just say this works for me. When I overnite I will run the fridge on propane just don't want to do it while driving. When you hook up the 7 way and start the car the alternator reads the car battery voltage not the pod battery so it won't fully charge very well. Again my charger charged my battery pretty quickly....I have an old automatic charger so the amperage input rolled off as it reached full charge. I haven't spent any additional money and can top off my battery if needed. Again it works for me not sure what the argument is about.
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Posted By: offgrid
Date Posted: 19 Dec 2020 at 11:36am
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I prefer to run my fridge on 12V while towing also.
But when we ask a question or propose something on a forum, we all need to expect questions and challenges, otherwise why ask? In this case the physics behind the energy flows is what it is, and it works the same for everyone.
Of course its totally up to you what you do or don't do with information you get, its your rig. No argument from me.
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
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