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Old 02-26-2021, 05:50 PM   #41
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Originally Posted by Jon Vermilye View Post
One place this makes sense is for those that depend on solar and do not want to carry a generator (and the gas for it) for those rare occasions where there is not enough sunlight to allow them to keep camping.
I think that might be me. At least, I would prefer to avoid carrying a gasoline-fueled generator.

We have a 160-watt solar panel with controller and a 225-Ah pair of conventional lead-acid 6-volt batteries as installed by Escape in late 2017. I anticipate the battery capacity has diminished approaching the 4-year mark.

To date, the solar has managed to keep up with our demands. However, as we have camped in the cloudy Pacific Northwest, I've watched the monitor panel on our charge controller and observed it sometimes approaching 50%, around the ≈11.9 volt level where charging should ideally be initiated.

I would like to know that I could someday use our Grand Cherokee tow vehicle as a "generator" to charge our batteries when boondocking, even if we are not able to accomplish a full charge. While I haven't looked under the hood to verify the particulars, I understand that we have either a 180 or 220 amp alternator.

Our usage includes the typical relatively low-Ah uses; water pump, LED lighting, DSI water heater, fridge control board, and interim use of the Atwood AFSAD12 furnace (which probably adds up as the highest use as we run the 3.4 amp fan). We don't make toast or coffee or run the microwave or other high-Ah uses. I'd guesstimate that we have gone through about 50-Ah or more in a day.

I have read on various threads about the required gauge of wire to accomplish charging from the tow vehicle, including parallel circuits with Anderson connectors. I've looked at the charge curves for lead acid batteries. I have read of DC to DC converters to manage the charge of the trailer battery. There was even a post at one point in the last year that mentioned running 120 VAC between the TV and the trailer.

This got me to thinking; our JGC has a 150 watt receptacle. If I were to run an extension cord back to the trailer, might this be effective in terms of providing a quick charge? Or would I be better off just operating through the 7-pin connector?

Or, to pose the question differently, which of the following might be good choices to explore in order to provide a decent supplemental charge in an hour or so of idling the Jeep without going too crazy in terms of expenses and/or modifications? (Acknowledging that some here have encountered objections from rangers regarding this practice.)
  1. $ - ≈14 gauge 120 VAC extension cord from Jeep power receptacle to trailer (using 15A to 30A plugset adaptor to make connection between cords).
  2. $$ - Making up a set of ≈25 ft long 8(?)-gauge "jumper cables" to connect from the tow vehicle battery to the trailer battery in camp.
  3. $$$ - Circuit to parallel the 7-pin circuitry through the tow vehicle and trailer with high-amperage connectors.
  4. $$$$ - Setting up a DC to DC charging system.
  5. $$$$ - Additional solar.
  6. $$$$$ - Small LP-fueled generator.
  7. Other.
  8. None of the above. I'm doomed!
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Old 02-26-2021, 07:21 PM   #42
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Mike.

If you only occasionally need to use an alternative charging scheme to supplement your solar, read post 20 on page 1 of this thread. You can hook an inverter (you can use jumper cables) to your TV battery and plug your trailer into it to charge your trailer batteries. It's not the most efficient, but who cares and it is space saving, uses existing wiring and it is low cost. You can probably only pump 300 watts into your batteries so you would not need an expensive inverter. A 500 watt pure sine wave inverter can be procured for less than $100).
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Old 02-26-2021, 07:36 PM   #43
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I used to charge my Oliver batteries regularly when we were out camping. I have a suitcase system, but with shade or weather it was not always useful.

I simply turned the truck around and connected a set of heavy duty jumper cables directly from the truck to the house batteries. This is simple and very effective. No inverter needed, unless you want 120 volts from a source outside the trailer.

Now, I do the same with a 50 amp Anderson plug. #6 wires run to the rear bumper of the truck, from the battery, with a breaker. And an Anderson plug on the tongue with #6 wires that go directly to the batteries in the trailer. This system is always plugged in while we drive, and used to charge if needed while parked.
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Old 02-26-2021, 07:38 PM   #44
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Mike.

If you only occasionally need to use an alternative charging scheme to supplement your solar, read post 20 on page 1 of this thread. You can hook an inverter (you can use jumper cables) to your TV battery and plug your trailer into it to charge your trailer batteries. It's not the most efficient, but who cares and it is space saving, uses existing wiring and it is low cost. You can probably only pump 300 watts into your batteries so you would not need an expensive inverter. A 500 watt pure sine wave inverter can be procured for less than $100).
That's a great thought. I already have a 300 watt pure sine inverter that we pack along in the trailer, double the size of the one built-in in the Jeep.

I can't remember why I bought it, nor am I sure if I've even used it yet.

That guy in post #20 is pretty sharp. Normally I read a thread pretty closely before I post, but I guess I just got all excited!
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Old 02-26-2021, 07:41 PM   #45
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I used to charge my Oliver batteries regularly when we were out camping. I have a suitcase system, but with shade or weather it was not always useful.

I simply turned the truck around and connected a set of heavy duty jumper cables directly from the truck to the house batteries. This is simple and very effective.
Having the batteries located under the rear dinette makes a lighter gauge "jumper" cable set advisable for both ease of routing and cost, unless I want to breach the hull and add a connection point.

Do you know about how much charge you could transfer in an hour or so?

I also seem to recall that you were the one who posted about the friendly ranger saying you couldn't charge your trailer by using your truck; but I won't tell anyone except the whole world here.
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Old 02-26-2021, 08:15 PM   #46
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Mike, I never measured the amps being delivered from jumper cables, but it charged faster than plugging the trailer into my 2,000 watt generator and using the onboard charger.

My Anderson setup, which isn't as fast as possible, is designed to put out 50 amps. It has a 50 amp breaker in the circuit that has never popped. Recently, the batteries were almost fully charged and I connected an amp-probe to see what it was doing (love the clamp on DC amp-probe). It was reading 24 amps. Direct jumper cables are likely to put out much more than a circuit with about 70' of #6 wire.

My new setup has the batteries under the dinette seat too. I haven't charged with the jumper cables on the new trailer, but it would be easy to come in through the window with the truck parked right next to the trailer.

Also, idling the truck is a much more pleasant sound than a generator droning along at 3600 RPM, or higher. I leave the generator at home.

I don't see any reason to connect an inverter to the truck, and then plug the trailer in the inverter. Unless you want to run power tools, or the microwave, or whatever. Even while charging from the truck with jumper cables, you can run your trailer's inverter, if it has one. It will be pulling current from the same posts the jumper cables are attached to.
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Old 02-26-2021, 08:26 PM   #47
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Mike,

If you go the inverter route the charger in your trailer will do its thing to properly charge the battery. How much charge you will get depends on the charger in your trailer. Here is some food for thought: Lead acid batteries typically charge at .1-.2C, where C is the amp-hour capacity of the battery (225 a-h in your case) which means you get 10% - 20% of full charge per hour. For your battery .1C is 22.5 amps, .2C is 45 amps.

Having some way to measure the charging current, like a victron BMV 700 battery monitor for example, is really helpful in analyzing and understanding these systems.
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Old 02-26-2021, 08:57 PM   #48
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Originally Posted by Raspy View Post
I don't see any reason to connect an inverter to the truck, and then plug the trailer in the inverter.
This arrangement seems handy in terms of not having to invest in more copper cable to carry 12VDC when I could use the 30-amp power cord that I'm already carrying as the 120VAC works well in carrying more power through a lighter cable.

I also wouldn't have to route cables through windows, etc.

When the battery in the JGC failed last year, I was surprised to find that it is located under the passenger seat; it reminded me of my days running the old air-cooled VWs. However, the Jeep has terminal posts under the hood for connecting jumpers. So, it would be really easy to hook up an inverter there.

I like your 7-pin-plus-2 arrangement. It's clean, it's there when towing, and it could be readily connected when set up at a campsite. However, it also requires an investment in time and cable when I still haven't got the home remodel here done to the satisfaction of all concerned parties.

While using an idling 5.7 liter engine as a charger isn't an approach I want or intend to use a lot, it is an approach that's expedient.
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Old 02-26-2021, 09:10 PM   #49
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Mike,

If you go the inverter route the charger in your trailer will do its thing to properly charge the battery. How much charge you will get depends on the charger in your trailer. Here is some food for thought: Lead acid batteries typically charge at .1-.2C, where C is the amp-hour capacity of the battery (225 a-h in your case) which means you get 10% - 20% of full charge per hour. For your battery .1C is 22.5 amps, .2C is 45 amps.

Having some way to measure the charging current, like a victron BMV 700 battery monitor for example, is really helpful in analyzing and understanding these systems.
From the fact that folks are investing a couple hundred dollars in DC to DC chargers, I infer that they are doing this to obtain more than just a battery isolator. I am guessing that, additional to operating as a charge controller, there is some voltage boost occurring in the DC to DC charger which allows it to provide a charge more quickly, if only to overcome the line losses from the vehicle.

In other words, I am guessing that a tow vehicle directly connected with cables to carry 12VDC to the trailer is not likely not going to provide as much current to the trailer as either the DC to DC charger or the 120VAC arrangement will.

Are these notions conceptually correct?
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Old 02-26-2021, 09:22 PM   #50
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Mike, I think if you dig deeper you will find most of the DC-DC isolators are associated with Lithium batteries which operate at a bit higher voltage than lead acid. LFP batteries can be charged from a constant current/constant voltage power supply, which is what the DC-DC isolator is. There are benefits to using one with lead acid batteries also. As you stated they can overcome voltage drop in the wires. If you intend to charge lead acid batteries this way, you should use a DC-DC isolator CHARGER designed for lead acid batteries.
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Old 02-26-2021, 09:27 PM   #51
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Possible all purpose solution.
Mount Anderson connectors to the vehicle and trailer batteries. Buy a heavy duty #10 or #12, 25ft., 110 volt extension cord. Make Anderson connector adapters for each end. Now you can easily connect the vehicle to the trailer for charging; use your new cable to connect a portable panel out in the sun; and you still have a good extension cord when you're too far from the camp power pole.
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Old 02-26-2021, 09:30 PM   #52
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Mike, the jumper cable thing is really best for emergencies. I did not have solar on my Oliver and sometimes we had to park in the shade. Having a solar system has been a game changer, even though it does have a few limitations.

Now, when we are completely off grid, I'll get up in the morning and plug in the electric coffee maker! It makes me laugh every time I do it. An electric coffee maker.

There is no way the Jeep alternator could hurt your house batteries while jumping them. It manages the charging of your Jeep battery all the time. That is what the regulator does. When it gets feedback from your batteries, it cuts back. And it seems many modern vehicle charging systems have a multi-step program in them. So, the car is a smart charger. But I think we should all have jumper cables with us all the time. They're just another tool in your kit.
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Old 02-27-2021, 12:02 AM   #53
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I appreciate all the engagement and information. It's given me some good ideas about how I can proceed for the present without investing much time or cash, along with things I can target in the future.

When you think about it, charging 10 to 20% of the rated capacity in a lead-acid battery in an hour is like 20 to 40% of the usable capacity, and that's exactly what I'd like to be able to accomplish. I figure 25-Ah would generally be great if I'm just supplementing the solar.

The "real" jumper cables live under the folding bikes in the back of the tow vehicle. So, they're always there, but at 8 or 10-ft long, they would not reach the trailer batteries in many of our narrow campsites.

My primary concern with my conceptual 8 or 6-gauge "pee-wee" jumper cables would be ending up with a much slower charge rate. In fact, BlueSea's ampacity chart indicates I would need about #4 CU conductors to limit the voltage drop to 3% in a 60-ft circuit. My concern is that if the vehicle's regulator is seeing the vehicle's battery at 14.4V and is tapering the output down, the charge rate at the trailer's battery would be low and slow. But maybe that's not the case - ?

I'll have to get the clamp-on ammeter out and do some checking. In fact, I should probably throw it in the trailer as camping is often the time when these kinds of things get some attention.

Raspy, it's funny that you mention the coffee maker. We bought an electric coffee maker with an insulated stainless steel carafe. When we don't have shore power, we heat water over the stove and then do a pour-over right into the filter basket. This turned out to be much faster than the large cone we used to carry, and with a little preheating the carafe keeps it nice and hot.
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Old 02-27-2021, 09:07 AM   #54
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Mike, I think if you dig deeper you will find most of the DC-DC isolators are associated with Lithium batteries which operate at a bit higher voltage than lead acid. LFP batteries can be charged from a constant current/constant voltage power supply, which is what the DC-DC isolator is. There are benefits to using one with lead acid batteries also. As you stated they can overcome voltage drop in the wires. If you intend to charge lead acid batteries this way, you should use a DC-DC isolator CHARGER designed for lead acid batteries.
We recently purchased a Soneil lead crystal battery (actually two 6 volt batteries) giving us 260 ah's. The bulk/absorption is 14.6 and the float 13.5-13.8. We have no problems setting our Victron controllers to those parameters, but our Escape provided converter is set lower than we wish and have yet to find a converter that has a float 13.5 - 13.8. Lithium chargers seem to be full charge (14.4 to 14.8) with no float value. We are looking for a converter to meet our needs, but perhaps will need to accept a lithium converter to keep our batteries topped-off.

In the meantime, we'll be at a RV resort for the month of March and let our Escape's 170 watt rooftop solar panel keep the batteries topped off.

OTOH, perhaps I'm worrying too much and should just let our solar panel do the job. Sometimes just writing let's you see the probable obvious answer.

EDIT: yup, our solar panels are the obvious answer. They should have no problems keeping the batteries topped off.

Enjoy,

Perry
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Old 02-27-2021, 11:40 AM   #55
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For those of you who need to measure amperage and voltage on your RV, this is what you want:


https://www.ebay.com/itm/PDF40-Porta...temCondition=3


Expensive but worth it. It will measure DC amperage flow through a wire down to 1/10th amp, and DC voltage down to 1/10th volt. I have had one for over 10 years.
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Old 02-27-2021, 12:37 PM   #56
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I have a fluke 325, which works well. It may be a bit more expensive than the PDF40. It also comes with a thermocouple which is useful for evaluating your refrigerator performance.
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Old 02-27-2021, 03:46 PM   #57
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Relying on your alternator while at idle likely won't suffice. This is the output graph of the 200 A alternator on my Ford. I don't know the ratio of engine speed to alternator speed.
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Old 02-27-2021, 06:55 PM   #58
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Interesting observation. Maybe you could measure the pulley diameters. Maybe a high idle would suffice.
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Old 02-27-2021, 07:00 PM   #59
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I don't know the ratio of engine speed to alternator speed.

Generally between 1:2 and 1:3 engine:alternator.
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Old 02-27-2021, 07:17 PM   #60
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I'm not sure what the idle RPM is but assuming 750 and a 1:2 pulley ration the alternator should put out at least 120 amps at max temperature. I can't imagine the truck using more that 20 amps (SWAG), assuming you have unnecessary stuff turned off. That leaves about 80-90 amps for something else. Worst case, it seems like a short stick to assist the accelerator pedal a little bit is all that would be needed, but idle should give you 30-40 amps. Sounds like a science project is in order!
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