Inverter on tow vehicle to charger in rv

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Re: Inverter on tow vehicle to charger in rv

Postby KTM_Guy » Fri Dec 21, 2018 5:17 pm

tony.latham wrote:
...because their high end AGM batteries are not getting fully charged...


I'm working out the details for my next build and I've got a little man that's sitting on my shoulder whispering, "AGM, AGM, AGM." I just told him to keep his elf lips zipped. :shock:

I've had no problems after four (or five?) years on my current lead-acid marine battery --charging while on the move from my rig and from the sun while parked.

Simple is good. :thumbsup:

Tony


"LiFePO4, LiFePO4, LiFePO4" Maybe Santa will bring you one. :worship: :thumbsup:

I'm at that stage now to buy a battery. Was talking to a guy on the phone the other day that has some close out 75AH Lithium deep cycles batteries. He said no one wants the 75AH they want 100+. But he was telling me all the reasons why I want to go with Lithium. And I agree with all of them. Then he said "Give me one good reason why you wouldn't buy one". I said "seriously? You don't think I can come up with one reason?" Good thing he didn't say two reasons. :lol:

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Re: Inverter on tow vehicle to charger in rv

Postby KTM_Guy » Fri Dec 21, 2018 5:30 pm

MtnDon wrote:
KTM_Guy wrote:My question is he said golf cart batteries, those are usually 6 volts. I'm sure they are wired is series for 12 volts. But what I have been reading is you should charge your batteries at the battery rated voltage. Noco who makes high end chargers even says to charge batteries wired in parallel should be charged individually.


Lead acid batteries in series connection are no problem to charging. That comes from years of off grid experience and a friend who has been building off grid systems for 25+ years. Parallel connections can have problems due to differences in internal resistance between batteries. Note that I started lead acid batteries. The typical flooded golf cart battery is quite forgiving to slight overcharges but not to being undercharged and never or seldom getting to 100%. AGM and other sealed lead acid batteries can be damaged by both over and frequent undercharging.


Thanks, that is interesting. I have been looking at the Vmax AGM's for my build. I was told they can be discharged 80% with little damage to the battery, if that is the case I could easily get away with a 40 or 50 amp hour battery for 3-4 days and not have to worry about recharging for most of our trips.

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Re: Inverter on tow vehicle to charger in rv

Postby troubleScottie » Sat Dec 22, 2018 12:23 am

As stated in the various posts, the major issue with just connecting the TV alternator to the TD is that the charging system is NOT a smart charging system.

Kind a amazing it works reasonably well keeping the TV battery which is very similar to many TD batteries.

To get near 100%, you most likely want a smart charger for the TD battery. So it will handle the various states of the battery.

As other have stated, there is lots on this topic.

A solution is to incorporate a DC-to-DC charger. The TV alternator is the source. There are lots out there eg CTEK D250S, several REDARC, ENERDRIVE. These solutions are smart chargers often with dual inputs eg solar and DC. They are pricey. So you are weighing the cost benefit of just using the TV alternator versus a very clean system.

You should not use the power connection in your towing harness -- too small. So you will have to run a separate pair of bigger gauge wires, with an isolator and appropriate fuse(s) from the battery to the rear of the TV. Think big audio amplifier in car. Then some waterproof connector ( Anderson - https://powerwerx.com/ ) Then more wire on the trailer to the battery or charger.
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Re: Inverter on tow vehicle to charger in rv

Postby tony.latham » Sat Dec 22, 2018 11:28 am

A solution is to incorporate a DC-to-DC charger.


This summer I ran into a couple that (literally) were living in their Camp-In. (If I recall correctly, they'd put 75,000 miles on it last year.)

They mentioned that they had historically had bad luck with AGM batteries until they installed a DC to DC charger. I don't recall the brand but they were happy campers.

:thumbsup:

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Re: Inverter on tow vehicle to charger in rv

Postby KTM_Guy » Sat Dec 22, 2018 12:27 pm

So the questions the OP had were.

Does he need a pure sine wave inverter and the answer was contact the manufacture. Which is a good answer.

The second question was "and what the problems would be?" The only answer to that was a 120v cord flopping around. Which can easily be fixed with some cable ties.

This has got me thinking it might be the way to go. I have a factory installed inverter in the Jeep (need to check the output) I have a smart 10 amp charger that would recharge my daily use in 1.5 to 2 hours driving.

I really don't see a downside.

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Re: Inverter on tow vehicle to charger in rv

Postby troubleScottie » Sat Dec 22, 2018 2:00 pm

My question is an inverter properly designed/cooled to deliver max power continuously?

The other question is what is the power needs of the battery charger. I doubt they are so efficient that they could deliver 10 amp @ 14v with only 140W of input power eg 1:1 on conversion. So would a 300 W inverter be enough?
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Re: Inverter on tow vehicle to charger in rv

Postby MtnDon » Sat Dec 22, 2018 2:26 pm

A good inverter should handle continuous running. Check the specs to see if there is a duty cycle.

I you have access to a Kill-A-Watt or similar device measuring the amps or watts being used by the charger when connected to house grid power and when charging a partially depleted battery will provide the most accurate answer to the power efficiency of the charger. The vast o majority of chargers are not very efficient. Sorry, but I can't be any more accurate than that. There are a few, much more expensive chargers that have very high efficiencies. Efficiency is not usually a major concern when plugged into the grid so most chargers waste power. They also have a large start surge, much like a refrigerator has a surge. Some inverters can handle a surge better than others.

Morningstar makes a great 300 watt pure sine wave inverter that is rated for 300 watts and is rated for a surge up to 600 watts.
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We have a small off grid cabin we built ourselves in the NM mountains; small PV solar system; 624 watts PV, Outback CC & inverter/charger ... http://countryplans.com/smf/index.php?topic=2335.0
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Re: Inverter on tow vehicle to charger in rv

Postby Andrew Herrick » Sun Dec 23, 2018 12:06 pm

KTM_Guy wrote:So the questions the OP had were.

Does he need a pure sine wave inverter and the answer was contact the manufacture. Which is a good answer.

The second question was "and what the problems would be?" The only answer to that was a 120v cord flopping around. Which can easily be fixed with some cable ties.

This has got me thinking it might be the way to go. I have a factory installed inverter in the Jeep (need to check the output) I have a smart 10 amp charger that would recharge my daily use in 1.5 to 2 hours driving.

I really don't see a downside.

Todd


Haha, fair enough!

If you want enough juice to power an inverter to charge a trailer battery, you can't - or at least shouldn't - just temporarily connect an inverter to the battery terminals. It needs to be fused, hardwired, protected from heat, water and dust, with sufficient airflow and clearances, and installed in compliance with all other manufacturer's instructions. You need to confirm the duty-cycle output of your alternator will match or exceed the power requirements of the inverter when connected to maximum load.

Here is an excellent resource about hardwiring an inverter to a car battery: http://wagan.com/blog/inverter-connecting/
And another one I liked about power inverters in general: https://www.donrowe.com/power-inverter- ... m#modified
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Re: Inverter on tow vehicle to charger in rv

Postby KTM_Guy » Mon Dec 24, 2018 2:03 pm

Andrew Herrick wrote:
KTM_Guy wrote:So the questions the OP had were.

Does he need a pure sine wave inverter and the answer was contact the manufacture. Which is a good answer.

The second question was "and what the problems would be?" The only answer to that was a 120v cord flopping around. Which can easily be fixed with some cable ties.

This has got me thinking it might be the way to go. I have a factory installed inverter in the Jeep (need to check the output) I have a smart 10 amp charger that would recharge my daily use in 1.5 to 2 hours driving.

I really don't see a downside.

Todd


Haha, fair enough!

If you want enough juice to power an inverter to charge a trailer battery, you can't - or at least shouldn't - just temporarily connect an inverter to the battery terminals. It needs to be fused, hardwired, protected from heat, water and dust, with sufficient airflow and clearances, and installed in compliance with all other manufacturer's instructions. You need to confirm the duty-cycle output of your alternator will match or exceed the power requirements of the inverter when connected to maximum load.

Here is an excellent resource about hardwiring an inverter to a car battery: http://wagan.com/blog/inverter-connecting/
And another one I liked about power inverters in general: https://www.donrowe.com/power-inverter- ... m#modified



Thanks Andrew,

The reason I ask is be cause I have and inverter from the factory in my Jeep, so it would check all the boxes you have listed above. My charger outputs 10 amp at 14.4 volts and draws 188 watts on 120v. I could have smart charging, not have to touch my electrical system, not have to run welding cable and relays. What if the best way was right under my nose all the time?

But it is all mute now because the inverter is only 150 watts. As far as going out and buying and inverter just for this for me doesn't make sense for me since I really don't need 120v while camping.

I'm checking to see if I can return (I think I am still in the return window) the Noco charger that I have and replace it with the CTEK D250SA. It probably makes the most sense since it is a MPPT solar charger too. And I was planning on adding some solar anyways. I don't have room for big panels some the MPPT controller would help. And the CTEK is just a little more than the solar controller and AC charger. And the CTEK will do it better.

I probably don't even need an AC charge because the battery would charge on the drive home from camping and the solar would keep it topped. Just hope I can return the charger I have. :worship:

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Re: Inverter on tow vehicle to charger in rv

Postby capnTelescope » Mon Jan 07, 2019 11:56 pm

MtnDon wrote:I thought there was somebody on the forum who had already done just what you are thinking of, but I can't find it. Maybe I'm dreaming or confused about where I saw it. As I think I recall, the person used it mainly while traveling. If the intent was to also use such a system while parked I would only recommend doing that as a last resort and only if a generator and charger was not available. It would be a fuel waste to run a TV engine while parked.


That was probably me, Don. It's in the Charge While Towing topic. Here's my experience:

It's roughly 30 feet from my TV battery to TD battery, so an inverter in the tongue box cut that distance in half. Because I only had LED lighting and the Fantastic fan, things were fine with 10AWG wire supplying a 300W inverter and a 7.2 amp charger. That was until I added a 12V Indel refrigerator. Then things started getting undersized in a hurry. Now a fully charged TD battery was good for about 2 days, and I was staying at IRG for 4. Charging from an idling TV didn't do all that much good, but back on the road things worked. However, the AGM battery had just sustained the first of several death blows.

First I replaced the 7.2 amp charger with a 25 amp one and the 300W inverter with a 600W one. Well, the 25A charger just dragged down the 600W inverter, so I settled for a 15A charger. The inverter kept giving a low voltage warning, and would cut out. I also got a small gas generator just in case. Just-in-cases turned into the "usual." The generator would run for hours just to bring the battery to Stage 3. Good Grief, I hated that genny. They may be quiet, but they're not silent. With the generator, beer stayed cold, but the AGM was taking some more hard hits.

This last summer, I went out to SoCal in the height of the heat wave. Total system failure. The heat was just too much. I'm pretty sure the problem was the inverter, but no way to test on the road. Ambient temperature this summer was hotter than the inverter was rated. So now the AGM won't run the fridge at all, and I'll be re-doing the whole setup and adding solar.

THE MORAL OF THE STORY is that DC-AC-DC charging has to be sized just as critically as your solar setup. Any weak link will result in great annoyance and warm beer.
I'll burn that bridge when I come to it.

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Re: Inverter on tow vehicle to charger in rv

Postby tony.latham » Tue Jan 08, 2019 10:40 am

Any weak link will result in great annoyance and warm beer.


Ger write up, as usual, Brad.

Me? Up here at 45ºN? Ice. :R

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Re: Inverter on tow vehicle to charger in rv

Postby Aguyfromohio » Tue Jan 08, 2019 11:17 am

We plan a high current dc line from tow vehicle back to trailer. Wire size is pretty important, we ended up at 4 AWG, bigger than one might think to avoid a significant voltage drop.
For a 120 VAC circuit, we don't care much about losing 3 volts, 117 will do just fine. When we start with only 12 volts we can't afford to lose 3 volts, that would drop us down to just 9 volts at the end of the wire. So you need huge wires to carry big amps at 12 volts.

For our system we are trying to use our 12 VDC tow vehicle alternator as an energy source to run our little air conditioner in the boondocks, so we bring the 12 volt power back with those huge wires. We figure the AC runs intermittently, so we are counting on charging the trailer battery during those minutes when the AC is OFF. It is more or less the same system you want to charge from the TV, and at a high 30 amp rate.

We should be wrapped up building and be camping this summer so we can report if it works in the real world.
Right now it's all theory.
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Re: Inverter on tow vehicle to charger in rv

Postby flboy » Thu Feb 14, 2019 1:34 pm

Lots of good info.. at the end of the day I think it would work albeit more complex than needed... TV to Inverter to Charger to CT. Each conversion of power costs in terms of efficiency so without deep analysis, I'd say probably about 50% loss of efficiency. You are converting no less than 3 times (DC to AC, AC to DC, DC to DC which technically is DC to AC to DC all internal). If I were to try it I'd do a couple of things.

1) inverter and charger needs to be in cab and protected from elements with good ventilation unless you have a good gauge wire back from TV to inverter in CT. Do not want to run 110vac outside and to TV. Just a shock hazard waiting to happen if wire is compromised during motion. If you do run the 110vac outside and back to CT for charger, a GFCI breaker after inverter is required for safety in my book.
2) proper fuses to protect both runs of DC wiring.. TV to Inverter and Charger to Trailer.
3) Maybe use a relay to switch power to inverter in TV to ensure it is not left on when motor is not running.

If you have to buy the inverter or charger to make this work, then I'd say skip right to a good DC to DC charger like a Sterling 1230 or Ctek 250s. If you have all the equipment, why not try it , but see 1-3 above.

So... having said that, direct DC to DC may get you most of the way and less complex and not expensive, but not charge 100%, which may not be an issue if you can complete with solar or generator at campsite. A good DC to DC charger will work for sure but set you back close to $300.

I am testing a TV DC to CTC DC system I just installed. Depending on performance, I will settle for a less than optimal charge or I will spend the $ on the DC to DC charger.

Good luck!

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