Idea for charging house battery

[Todd & Meg]

I am building a teardrop trailer that will have a house battery. I haven't decided on the size yet but my daily use is around 15 amp hours give or take. That would go up if we get a 12v fridge. If we do get a fridge it will live in the back of the Jeep and run off the Jeep when we are driving and then when we stop we'll have a wire from the trailer to the back of the Jeep.

I have been looking at options to charge the battery. It looks like there are a few choices.

Solar, I live in the southwest so it's hard not to consider it. Pros are not to expensive, with the 15 AH I'm planing on using recharge could be 2-4 hours. Option on panel sizes, I could go with two 50 watt and use one or both depending how much charge I need. I think I could mount a 50 watt on the top rack when the rack isn't needed, that way I could charge even when driving. Cons, Not always having sun, Having to pull panels out when you stop, having a place to store the panel we said nothing is to be stored in the cabin on the bed. Theft of panels is an issue so can't leave the campsite with them out.

Charging off the Jeep .Pros free power, can't beat that. Cons, might have a hard time fully charging an AGM battery without going with a DC to DC charger ($$$), or play games to fool the charge system to put out more voltage. It's slow depending how much other load there is. Nothing to really control the charge unless you spend big money on a charge controller. Have to run #10 or #8 wires from the Jeep battery to the trailer battery with fuses.

Crazy third idea. I have a Noco 10 amp charger that will be in the togune box with the battery to charge when we have shore power. Our Jeep has an inverter (300 watt I think) built in. You can see where this is going. All I need is an extension cord and I can charge the battery in 1.5 hours or so. We rarely stay in the same place for more than a few days, and I can size the battery so we can run for a few days without charging.

So what am I missing why wouldn't that be the best way to go. The only problem I can see is the charger has some smarts built into it and may need a pure sign wave inverter which I'm sure the Jeep doesn't have. But that is something I can check on.

Any thoughts?

Todd

 

[smritte]

Too much loss going from inverter to charger. If you were going to do that, use the Jeep to charge battery directly. The most the battery will pull is 20-40 amps. Make sure you have a big enough feed wire for charging. I ran a 4 gauge feed to the back for that (a bit overkill). I have a 120 watt panel and will probably change it to two 60 watt panels this next season. I also charge trailer battery while i drive. My off-road trailer has a 50qt fridge and I don't remember the battery size (90AH?) but its not very big. I can go a day and a half without charging if its not real hot outside. If it was, I have more than enough sun to charge with. Takes about 2-3 hours of sun to charge after what was used overnight.
I use to have a small camper on my old truck that I would tow my jeep with. The jeep and truck had same battery. I would swap out batteries in morning and charge while i drove jeep. That's before I got solar.
The best place I found to get panels is Solar Blvd https://www.solarblvd.com/.
These guys are very helpful and have used panels as well as new. My 120 watt American made panel was $90. It was a 5 year old panel with 15 years left on the warranty. The life span of it is at least 20 years if it's in the sun all the time. I store it in a compartment. It will probably out live me.

Scott

 

[Steve_Midlands_UK]

For many years I used a 100w Solar panel to charge two 130ah batteries. The main draw was a 48w compressor cool box.

We would get about 3-4 days off grid as the batteries gave power but as solar Panel was doing all the work the cool box would JUST stay cold if it was a reasonably sunny day ...

We only did 5 days between drives to charge the batteries again .

 

[Todd & Meg]

Too much loss going from inverter to charger.

Scott

I know there is a loss if using an inverter off a battery but if running off an inverter while driving I would have an endless supply of power. And I would have an optimum charge using a smart charger. I wouldn't get that charging off the Jeep battery and if I go with AGM I may not get a full charge.

I have been looking into solar and may go that way but got thinking what if I have a better cheaper solution right under my nose and not even know it.

Todd

 

[SubeeBen]

Look up progressive dynamics pd4045kv from teardroptrailerparts.com. Panel does everything charges battery also has spots for 110v breakers & 12v fuse panel. & with a ground to shore electrical outlet on the trailer you can plug into the house to keep battery charged at all times. It’s a 1 step electrical panel for your trailer & very simple install. I used this on our trailer build. Just my 2 cents if that helps.

 

[Temudjin]

A couple of things you may be aware of, but just in case . . .

1. Your alternator in the vehicle is not an endless supply of power nor is it free. Running the alternator costs you fuel - it might only be a small amount but it comes at a cost. The alternator output (voltage and amps) is limited by the design and age of the alternator and the maximum output only occurs when battery voltage is low allowing maximum volts & amps into the battery. As battery voltage rises with charging the incoming amps drop off as a result. The closer your battery is to full charge the less amps come into it from whatever source you are using to charge it.

2. Someone else above suggested you avoid the inverter to battery charger to battery route and I would agree. There are definitely losses going from 13.8v (the nominal voltage of most auto electrical systems) to 110v via the inverter and then back to charge voltage which is again limited by the charger's capacity and the battery voltage and state of charge. The real risk here though is having 110v running in the system as a short circuit could be very serious. Electrocution via metal body panels and fire due to high voltage in a short would be the main worries. All in all, direct charge from the vehicle alternator is a simpler, safer and more effective solution.

3. Charging from solar panels has the same issues as charging from the alternator with volts and amps going in not being at maximum throughout the charging cycle. Charge volts and amps are highest when the battery is at a low state of charge and drops as battery voltage increases with charge. The other issue with the panels is that you only get maximum power out of the panels (not necessarily into the battery depending on state of charge) when they are in full sun and angled correctly. And they provide little or no power in cloudy conditions or when badly aimed and angled at the sun. That implies that they need to be moved multiple times throughout the day to ensure maximum charging.

4. Batteries - lead acid, AGM, deep cycle calcium or even lithium - should not be fully discharged as this seriously shortens the service life. For all except lithium you should not discharge below 50% of capacity which means a 100 amp hour battery only gives about 50 amp hours of usable capacity.

5. In any low voltage system (as in a vehicle) the current (amp) losses through long wiring runs become severe very quickly. And lost voltage results in much slower charging as well as lower final battery voltage, amperage and state of charge. So you need to keep wiring runs as short as possible and ensure you use a wire gauge big enough to do the job and of course thicker wire costs more and is more difficult to solder and install.

Sorry this has been a bit long but it's better to have a complete picture so you can design and build an efficient, effective system at lowest possible cost. I hope this helps.

 

[Steve_Midlands_UK]

Agree with above, double check your alternator max output as inverters can have surprisingly large current consumption.

I had a 7.5 tonne truck, because it was designed to be on the motorway for long periods with basic electrical needs the alternator was only 20-30A ( at 24v) had to upgrade it to charge a domestic battery bank.

 

[MazeVX]

So I think the inverter thing is done... Just makes no sense, there are charge boosters, works like a charger but is powered from another 12V source. Solar panels will give you power whenever it's not dark, so that is the best thing, solar panels hard mounted to the teardrop and all should be fine.
There are combined electronics that can charge with shore power, solar and from your jeep while driving that should be enough to stay out for a while.

Modern solar panels working really well in cloudy conditions or under a not ideal angle and should always be oversized , let's say you want 100W buy 200W panel from what I know and what I have experienced most go for 150-250W panels depending on the area, I would go for 250W for Europe as an example.

 

[Todd & Meg]

Thanks for the replies everyone. I got the Jeep's manual out today and the built in inverter is only 150 watts. So I can't use that for my battery charger which draws 188 watts. I'm going to see if I can return the AC charger I have and get the CTEK DC to DC charger. Since it is also a MTTP solar controller it's probably not a bad price. If I can add a solar panel , even if it is a small one like 50 watts I probably wouldn't need an AC charger.

I have spent so time looking into using an inverter to power an AC charger and most there is little info out there. I found mostly people saying it won't work but with no reason why not. I did find a few post where it was recommenced. But most say just run a wire with two fuses from the battery to the house battery and it is good to go. Well from what I read even with just 1/2 volt drop due to, to small of wiring you will never get a full charge. From what I can tell even with wires two sizes bigger you still won't get a full charge, and with an AGM not even close. Read one post where a guy was ripping AGM's because his failed in less than two years, got them replaced and the second set were them failing. He had 2-100AH batteries at the back of a 5th wheel camper using the stock 7 pin connector with 10 gage wire. And it was the batteries fault.

Have a Merry Christmas everyone.

Todd

 

[MazeVX]

Thanks for the replies everyone. I got the Jeep's manual out today and the built in inverter is only 150 watts. So I can't use that for my battery charger which draws 188 watts. I'm going to see if I can return the AC charger I have and get the CTEK DC to DC charger. Since it is also a MTTP solar controller it's probably not a bad price. If I can add a solar panel , even if it is a small one like 50 watts I probably wouldn't need an AC charger.

I have spent so time looking into using an inverter to power an AC charger and most there is little info out there. I found mostly people saying it won't work but with no reason why not. I did find a few post where it was recommenced. But most say just run a wire with two fuses from the battery to the house battery and it is good to go. Well from what I read even with just 1/2 volt drop due to, to small of wiring you will never get a full charge. From what I can tell even with wires two sizes bigger you still won't get a full charge, and with an AGM not even close. Read one post where a guy was ripping AGM's because his failed in less than two years, got them replaced and the second set were them failing. He had 2-100AH batteries at the back of a 5th wheel camper using the stock 7 pin connector with 10 gage wire. And it was the batteries fault.

Have a Merry Christmas everyone.

Todd

That's correct, your batteries will fail prematurely and that is the reason why I recommend to use a charge booster and luckily you got one. The ctek is known as pricy but reliable. This will be a good setup!
Merry Christmas

 

[phxdsrtrat]

Check you manual to see if you can force your alternator into a higher voltage mode. My GMC Canyon drops the voltage to as low as 12.3 volts when I'm cruising on the highway. However, this can be overridden by activating the tow/haul mode which bumps the voltage up to 13.8. I know for some vehicles, simply turning on the headlights will force the alternator into a higher voltage mode.

In the end, after much research I ended up mounting a Redarc DC to DC charger in my trailer. The unit can act as both a solar charger and DC to DC charger from the vehicle. Of course, this wasn't a cheap solution.

-Curtiss

 

[whiskey7backroads]

I built a custom trailer and only used solar. I used a trimetic tm2030 and it was awesome. If done right it will tell you your live draw and exact amps going back in. You can hook up other charging sources also..ie landline charger and or alternator. If doing again I would add alternator into equasion if not cost prohibitive. Then your covered in all situations as much as you can... Over size any battery bank.