This $20 Hack ACTUALLY WORKS as a DC-to-DC Charger for RV Chassis Battery | RV With Tito DIY
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- Опубликовано: 8 апр 2023
- Do you have a Lithium Battery Bank? Here's how an inexpensive PWM solar charge controller can be used to trickle-charge your RV's lead acid chassis or truck battery. Let me show you how it works.
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PWM Solar Charge Controller (20A) - amzn.to/40Zxl15
(Optional) Circuit Breaker (20A Ignition Protected) - amzn.to/3maJBwJ
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That is so creative and simple!!! Wow great job finding this application for pwm controllers. Always great stuff, thanks Tito
Thanks bud. I appreciate it. I literally have a bin of old PWM controllers sitting around waiting to be used for something.
Can this be done in reverse, when you’re driving? From the chassis battery to the house battery using the same charge controller, or would you have to use an MPPT version.
I'd recommend a better DC to DC charger designed for that purpose like a Victron 30A DC to DC. It will handle the higher current draw and battery compatibility much better with lots of settings for you to customize. Here's a video to check out ruclips.net/video/lvOYUfSBlmM/видео.html
This is just... genius. I have no clue why this never occurred to me before, but this is perfect, so spot on! Our batteries are quite far apart in our rig, and this would easily allow for smaller wires, easy run... Thank you!!
Yes. Try it. Same setup, just longer cable.
I know right what a great idea.
Thanks Tito
That's way more efficient than what I've been doing, plugging a trickle charger into the RV inverter AC circuit when I'm in storage. Thanks!
Yes. I used to do that too.
I've actually thought about doing this with a cheap PWM controller but going the other way from my tow rig to my travel trailer. It charges pretty slowly while charging with just the 7 way connector but I ended up putting solar on top of the travel trailer and it eliminated that need but it also allows me to maintain the tow rig battery while parked if I leave them connected.
Brian great job!
I learned from acid battery manufacturing that you lose 1% of your battery charge every day. I’m not talking about parasitic loads. The battery itself loses the voltage. So what you propose is excellent.
Yes. That's true as well. Thanks for reminding me.
Good job as always Brian!
Thanks Gary!
Thanks for the setup and explaining how that works.
You bet!
Brilliant idea.
Thanks!
I added a Votronic Standyby Charger to my campervan to stop the starter battery going flat when parked up. It uses excess solar once the house battery is charged to trickle charge the campervan starter battery. I added a fuse and a switch - so we can turn it off when we are driving. The unit is very small and very easy to instal and cost about $20-30. Its been a great addition, we no longer have an issue with the immobiliser and central locking systems draining the starter battery when the campervan isn't in use.
Thanks. That’s just what I needed to know.
That's great video👍👍👍
That is a cool hack. You da man Tito!
You da Mileage Master :) Haha. Thanks.
This is great!! I wanted to rig in a simple inexpensive way to run current back to the cranking battery as I was worried I would drain it too much from useing the radio or something!! my 200ah LFP house bank can so easily run a small charger for 10-15 min to get the cranking battery able to fire the engine! Fantastic!!
Glad you like it. Give it a try. It has been working great for the last year.
@RVwithTito What kind of amp transfer are you getting? my results have been very low, 3-4 amps at best with the cranking battery at 50% SOC. I think it is because the PWM controller cannot get enough voltage from the LFP battery to really enable it to push out to the PB battery. They are setup for PV input of 25ish volts likely, so. Tried a 20a PWM solar charger. I was hoping for more, my plan is to use this as a safety to assist if my cranking battery went dead from say using the Radio or something like that. This is in a small camper van where the stereo is the van dash unit. If it gets drained to the point the van wont start, this will take hours to put in enough to turn it over. I also am setting up a cut off switch from the + on cranking to the input of my DC2DC charger as it uses voltage sensing to turn on. Basically it has a built in VSR, so I don't want that to sense the power input from this charger.
Man, you are a wealth of knowledge. Thank
Glad to help ☺️
Awesome idea
Thanks!
Looks like another great idea Brian. I am going to do this.
Yeah. Give it a go!👍
Very cool mod Brian 👍
Glad you like it!
Great idea! (who's surprised?) - I had installed a trickle charger for the chassis battery that connected to my house 110v circuit, but this solution is better. Thanks AGAIN Brian!
Great idea! I'm going to the same thing thank you
Glad it was helpful! Good luck.
Cool. Clever too, as usual. 😎👍
Glad you liked it :)
Thanks! Great plan that makes a lot of sense, I actually have a cheap pwm to trickle charge start battery, but with a solar panel. Your way is much less "involved"
Yeah. Put that solar on the roof instead to charge your house :)
I like that idea. Even if it's not active all the time you can turn it on when needed.
Definitely. I thought I'd only turn it on when needed, but now I just keep it connected all the time.
So wish I could hire you to just look over my system and make a recommendation for improvement. I am confused on how to be sure it's working correctly.
Here's a list of folks that might be able to help you - rvwithtito.com/rv-solar-installers
Thank you for sharing this. Preparing to install our lithium batteries this week which will require either modifying the existing Trik-L-Start or buying the one you use. Looks like I'll be ordering a PWM charger.
Again, thank you for sharing!
Doesn't hurt to try :)
Thanks!
Thank you!
Thanks Tito, You're the best on RUclips. I have been a full timer since 1997 so I have been around a while. When I need accurate and friendly advice on additions or repairs to my full time Safari Serengetti pusher I look to your Channel first. Safe travels and hope to see you out there some day. RV Coach Hotel California
Thanks for the feedback. I'll try and keep it interesting :)
Another great idea! This is just what I was looking for as the Trik-L-Start and Amp-L-start are no longer available to keep my starter battery charged.
Awesome. Good timing. Good luck with the project
Sounds like a great idea of a way to mix batteries in a trailer (house, operational) keeping them charged, and still separate ststems.
Thanks. Yes. Works great!
Clever!
Beware that most charge controllers do not like to have an input connected with no output connection ( your breaker opened). I have a few Morningstar Sunsaver controllers that have this warning with them, and many others I have used are the same.
I have a small cheap mppt that takes its power from the solar array. It implicitly states that you MUST connect solar first and battery last. Always refer to the documentation for your device.
@@ssteele1812 The device he used has printed right on it "Connect battery first. Connect solar panel finally." So this should be good. Mine arrives today. 🙂
Your timing of this video is impeccable. My chassis battery just died from sitting without use. I did some You Tubing and came across an item called "AMP-L-START". Unfortunately, that company is no longer in business. This set-up you have will work great for me, although my house and chassis batteries are not in the same compartment, so a cable run will be need for me. Thanks again.
You're welcome. Sounds like you've got a plan 🙂
Thank you for the prompt response to my request and I'm sure the request of others, with this video. So obvious, and I didn't think of it. I have a small pwm controller sitting on my workbench doing nothing. And instead of thinking of this genius trick, I spent a significant amount of money buying a high amperage diode to create a bridge between the battery Banks to take advantage of the half volt drop across the diode. Now I guess I will be rewiring to employ the neat little four-stage controller like you did.
:) May as well put that PWM controller to good use.
@@RVwithTito On my diesel truck, my starter battery drops to 10.0 volts when cranking, if I had a pwm charger hooked up like yours the breaker would trip every time. I think you could wire a relay with the ignition so the pwm charger is disconnected for starting and then switch back when the ignition key is off. That would be the only way for it to work with a pwm charger. A small 10 amp mppt charger would fix the high current problem when the starter is used but I don't think it would work because mppt chargers need a slightly higher voltage on the input than what the battery it is connected to has.
I have an inexpensive PWM controller connected to my truck battery with a 25 watt solar panel. At full output the panel will put about 1.8 amps into the battery.
Yes. These days, there are tons of PWM controllers around.
I use a small 12v 10w solar panel to the tow vehicle battery when the truck is idle between rv trips
My Forest River C class has a switch on the side of the driver seat that allows you to tap into the house batteries if your chassis battery is too weak to to start the rig.
This is exactly what i was thinking of for my rv as well. I just purchased a red arc DC to DC charger that cost me $250 but have not installed it yet ... I think ill keep it and get this MMPT controller instead. Great video.
So what this PWM controller was able to do is that is that it connects from your car led acid battery which is already connected to the alternator and then takes current from there and charges your secondary battery which can be protected using an MCB. Am I correct?
@@grvsays Not sure what you mean by that but what it does is allows your house battery to be charged by the solar panels when not in use and then when you are driving and the engine is running it isolates the main and house batteries so no damage accours to each.
If you install a Victron Cyrix li ct, the solar or generator or shore power will charge house and starter batteries at the same time then separate them if either isn’t getting charged . You need to swap the battery isolator to a lithium isolator and tie in the boost switch. High power alternator charging 60-120 amps hr. If it detects charging on either batteries it combines them so it can charge the chasis battery from solar, generator & shore power automatically or vice verca for alternator charging the lithium’s
True. Lots of ways to get it done :)
This really isn't a good idea for normal use. PWM works by shorting PV to battery, and they can't effectively modulate current, so there is a potential for massive surge from the LFP to lead acid. Fuse on both PV and battery wires is critical. The experience with blowing fuses during start illustrates my point.
Cool. I wonder if simply installing your circuit breaker and a diode on the positive terminal would do the same thing?
Your multiplus ii has a built in 4amp trickle charger for starting battery. Even if not using the rv, just leave inverter in charger only mode.
Victron MultiPlus 4 Amp will work for this just fine AND you do not have to leave it on charge. The 4 amp trickle icon all the time. Works great.
Hey, I just run Separate one 320 watt panel just for the coach battery it works. I was watching some of these big rig fifth wheel units dam i had to change channel after seeing there setup Surprise it hasn't gone boom.
I Cringe some of these people that install solar on RV's. Specially some of the mobile techs. Under sized wire no fuse or breaker or disconnect. Terminations that look like 3 year old did it. Its getting to the point that solar inspections are needed on RV'S.
Seen ext. Plugs no sealant right over the firefly board. What's bad is they pack them in at RV PARKS if one goes a lot are going to go with it. I do Separate in order if I have any problems it's easier to diagnosed Then having it all tied in and everything
I do something similar with a victron cyrix bi directional 120 amp relay
Tuurlijk werk dit zonder problemen
De mppt of pwm charger in put is flexibel.
Je kan dus een mppt gebruiken om je lipo4 om te laden met je dynamo van je auto.
De mppt ziet gewoon 14.6volt van de dynamo en zet dat om naar de lipo4 charging profile.
I was actually thinking of doing something like this but a little different. I don't have a motor home anymore. I downsized to a small fifth wheel. I was thinking of using a PWM controller as a DC to DC charger from my pickup trucks alternator to the trailer batteries. I figured it would be better then that anemic connection that exists on the truck. Also, I have a 20 Amp PWM and it wouldn't cost me anything but some time.
If you have lithium batteries in your fifth wheel, then you'd still need to limit the current somehow or they could pull too much current from your alternator. When the current exceeds the PWM controller rating, it may just throw a fault and shutdown.
@@RVwithTito I still have flooded batteries but will be going to lithium soon. You bring up a good point though. Thanks.
Brian, did you consider the trickle charge output on your Multiplus II? Just got my MP2 and was wondering if that could serve same purpose.
No. I haven't tried it. Give it a go!
It will and it does. It is always on even if the MP2 is in the off position. Put a switch in line to shut off if ever needed.
I have a question regarding the 4 stage charging profile to the chassis battery using a pwm controller and if the input voltage is steady around 13.2 to 13.4 volts, how can it meet the higher 4 stage charging voltages 13.6 to 14.7 that the battery manufacturers recommend. A good trickle charger will meet these higher charge voltages and you won’t have to worry about blowing the fuse or breaker after starting the motorhome. As somebody else mentioned I use a good trickle charger on the chassis battery that is powered from a maintained ac outlet, shore power or inverter.
Brian,
Hi Brian, I wonder if you don't need an ignition lead to interrupt the output current from the Huine when you are driving. I have upgraded my coach much as you have but I've not yet installed a trickle charger to keep the chassis batteries charged.
I'm thinking that you may have created a power wasting current loop when you are driving. When you are driving the Victron DC/DC lithium charger sends current from your alternator & chassis battery to the lithium batteries. In turn, the lithium batteries are sending current via the Huine charger back to the chassis battery creating a power wasting loop. It may not be much, that's hard to assess without knowing the state of charge for each battery and the specs of the Huine, but it may be prudent to use an ignition lead to interrupt the Huine output to the chassis battery when you are driving.
Best regards from down the road in Kingston.
Take care,
Bob
You make a good point, and that's a great tip, but I don't think it's a problem in my system. Let's assume the alternator circuit runs between 13.4v to 14v with the engine running. In this state, the chassis system voltage would be higher than my house voltage which usually doesn't get that high when under load...always (even while solar charging). So there shouldn't be any current flow through the PWM charger even as the charger switches to float (given the measured chassis voltage). Nevertheless, I still think your idea is something worth implementing just to clean it up. Thanks 👍
Can the ground wire from the charge controller be connected to the frame of the vehicle instead of directly to the starting battery ground?
Hello, I want to replace the batteries of my motorhome for a 300ah lithium. I bought the victron isolated smart dc-dc 12v 30 amps. Can I connect the victron changer with the wires coming to my auxiliary batteries (by adding a 60 amp fuse protection at the input to the output) now to my new lithium without modifying the old installation...
If you already have a DC-to-DC charger that charges from Chassis/Generator to the House battery, make sure it is only ignition enabled if you do this hack. You don't want both "on" at the same time.
Hi Tito, great idea. I have a left over (lead acid only) Blue Sky MPPT controller that should work as well. I'm thinking; connect it in parallel with the lithium EPEVER MPPT controller on the PV side. That way the PVs will be charging both the lead acid and the lithium when the Sun is out. I prefer that rather than charging the lithium batteries from the PV then charging the AGM from the batteries. My question is; can two controllers be connected to one PV array? Also, if this would work, which ever (or both) battery banks need charging, they will get charged. What do you think? (on my RV, some devices still run off of the AGM (as well as the parasites) so the AGM needs about 5Ah per day. I have to figure out how to rewire everything so I can eliminate the AGM. There's no wiring diagram for the RV.) I'm not concerned about the chassis battery, it's good for months.
Pretty cool. Curious if this performs better than a B.I.R.D (bi-directional isolator relay)?
Not sure
If the fuse disconnects, it will blow the pwm module. They all say you have to hook up the battery first or you damage the controller.
Now that's a great idea for another idea I have been playing with 🙂
Let me explain: My dream is to have an electric RV, but our budget keeps that firmly in the dream world. The only thing in reach for most of us is to have enough solar and batteries to dry camp without the need for a generator. Another thing a person can do to consume less fuel is to take load off the engine by explicitly not using the engine's alternator to charge the house battery bank. Leave that to the solar array. With your trick we might be able to go one step further and take the whole damn inefficient alternator with it's inefficient belt drive off the block and use solar to power all electronics and lights needed to drive the RV.
Too weird? Remember racing cars drive without an alternator too.
Intrigued. Your idea is not at all weird, especially with rising fuel prices. Not sure how the setup would run everything that normally runs off the alternator. ?
Yep. Whenever I finally decide to go for it I would first measure the amp draw under the heaviest load and then choose an appropriately sized charger. It helps that I already converted the largest part of the lights to LED, so that should make a big difference. 20 amp might just be enough. Then after a test period I could remove the alternator and put a shorter belt in.
One thing just popped in my mind though: cheap mppt chargers are typically connected to 12V panels, and those 12 v panels are *not* 12V. They are more like 19V. The voltage of the house batteries will probably have to be cranked up.
Usually the limiting factor is the amount of space you have available for solar. If that's an issue, then alternator charging is usually the fallback.
@@RVwithTito Agreed. It does have some pitfalls though. When a modern car/RV starts then the ECU keeps the charging voltage high, 14.4V or so. Then after some time it drops back to a lower maintenance voltage, perhaps 13.6V. If the mppt charger can keep the voltage of the car/chassis circuitry above that 13.6V then the alternator will most likely quit generating power. That will certainly reduce load on the engine. I don't believe a simple MPPT charger will be able to deliver 13.6V when it's input is also 13.6V (or lower).
By just completely removing the alternator the losses generated by the belt will be gone too. Just as interesting is that the ECU won't be able to command power from the alternator ever. Not even when the voltage drops to 12.6V, and I think an MPPT charger will be able to deliver that voltage when there is only 13.6V coming in.
What if the battery bank is low and there is no sun? Hopefully that is a rare case because then I would have to run the genny to keep the engine running 🙂
T man strikes again!
This is a great idea. That parasitic discharge has been bothering me for years. I just happen to have a Harbor Freight CC that I've never used. It will work perfectly for this. How did you know about the power surge at startup?
I have a fuse inline on the battery side. It would blow when I started the engine. I would remove the fuse before starting the coach. The circuit breaker I'm using says it's ignition protected and seems to have solved the problem.
@@RVwithTito Brian, any concern with a possible charger overlap/loop between this charger from the house batteries and the Orion DC-DC charger from the engine battery/alternator that charges the lithium coach batteries? If both were slow to cutoff there might be a period when they are both on causing a loop. Great video and idea. I am just planning an inverter and battery upgrade to our 2007 Winnebago Diesel coach. So I am sorting out the extra items needed. I currently have a Trik-L-Start engine battery trickle charger which Winnebago started installing about the year of my coach. This charger may not be compatible to Lithium voltage levels, I am still researching. Thanks!
I actually didn't use the controller's solar input. I connected the house batteries to the battery input and then connected the chassis battery to the load output. Seems to be working well.
I have a question for you we just purchased a 2020 holiday rambler that has a factory installed 100 W solar panel with a 2000 W inverter can I add extra panels to the existing panel on the roof? some people have told me that you cannot do it.. it Has to be the exact same panel is that true or false and if I can, how many panels can I add to the existing panel?
And also one extra question if I am able to hook up extra panels, do I hook them up in series or parallel?
I really didn’t wanna add a whole new system with new batteries and inverter and solar charger
I would really appreciate your expertise on this matter….thanks,Frank
Nice job .
Could you use the same type of controller to take power from alternator to the leisure batteries.
The dc to dc chargers are a lot more expensive
The voltage supplied by the alternator may drop below 14V, so it will not be able to charge the lifepo4 battery (typically PV controllers can reduce voltage but not increase). However, this can be easily remedied by adding a step-up DC-DC converter where you can also set the minimum input voltage, so that charging will not start until the engine is started. A 20Amp step-up converter costs ~$20.
Great idea. I have small RV trailer with 85 amp lead acid battery. I plan to upgrade to lithium in 2024. I have a 100 amp lithium diy power station for night use. Your idea may work to keep lead battery charged at night for gas furnace and fridge. I can use the PWM to charge power station with my ground portable solar panel. What do you think?
You're power station doesn't support a solar panel input? Nevertheless, I also use a lithium power station in my tow car to keep the battery topped off...no controller though, just direct connect.
@@RVwithTito i do charge the diy power station with a separate MPPT controller but your idea works better with a PWM for both lithium and lead to charge the lead battery at night to help with the gas fridge and heater power. Thanks. i purchased a different PWM for lithium and lead.
My 2020 Forester Class C has a switch below the driver's seat that does just that... gives a jump from the coach batteries to the truck battery. Never tried it in that capacity but I hear it make a noise when I activate it just like a booster would... thanks!
Yes. That's an emergency start switch. It temporarily joins the two batteries in case (1) your engine won't start or (2) your generator won't start. The relay (clicking you hear) is located inside the driverside engine bay (probably).
Nice. So your lithium is acting as a " solar panel" to trickle charge your lead acid.
Essentially yes. Your solar panels are basically just a DC power source that fluctuates quite a bit.
Do you use this instead of a dc to dc charger. Does it protect your alternator. I just installed 2 lithium batteries. I was told I’d need a dc to dc charger to protect the alternator.
Will your hook up be worked with DCDC Charger in place? Thanks
Yeah. Probably but there should be little to no current flowing while the engine and DC2DC charger is running. As another guy suggested...adding an ignition cutoff relay is something to consider as well.
I installed this in my RV and the 20 amp breaker keeps tripping. It's because the Huine charge controller output is rated a 20 amps. So, you really need a 25 amp breaker with 10 gauge copper hookup wire to meet NEC code. I'm very concerned that the wire leads on the Huine controller are measly 16 gauge aluminum. Perfect for starting a fire. I've since tossed the controller in the trash and am planning to replace it with a Renogy PWM controller that charges at 10 amps, which is plenty for trickle charging my battery.
Says max solar input voltage is under 50v. I wonder if it would work with a 48v (51.2-54v) LFPo.
That might be a push. You could always put a 48V to 24V step down buck converter between the 48V bank and controller - amzn.to/41dpm0h
Question for you: what size wire did you run for this (it looks like the charge controller is using 16awg?
Second question : are your positive and negative leads from the small charge controller mentioned are they running to your Victron Lnyx power in or are they connected directly to the lithium batteries as mentioned in your video? If they are connected to your Victron Lynx what size fuse would you recommend? 20amp or 30? I try not to connect anything directly to my lithium batteries other than my Tfuse and smart shunt…TIA
The Huine charge controller can output 20 amps, so NEC code requires 10 gauge copper. The measly 16 gauge aluminum leads on the Huine are a fire risk in my opinion. Renogy sells a 10 amp PWM charge controller for $20, but I'm not sure if it can operate at the low voltage provided by the lithium battery.
Can it work in reverse.Can i connect my 10amp pmw solar charger to my car battery so i can charge my sla secondary battery while driving like a Isolator.?
i am curious what gauge of wire you used for your DIY dc2dc charger
For this low current trickle charge setup I used 12 or 14. For my other Victron DC to DC setup on our previous RV I used #6AWG.
Why not AGM to AGM? Should work like the expensive DC to DC chargers.
did you have to discount the charger that already on the rv that used to charge the house batteries with the alternator?
Nope. There was no alternator charging for the house.
@@RVwithTito thx
My apologies for interrupting this video thread; however, 3 years ago you did a video concerning your shattered shower door, I may be blind, but I didn't see a followup video. Did you make one, and where in your video library is it? Thank you
No problem. Here's what I ended up doing ruclips.net/video/Z_WoxSugaME/видео.html
We ended up liking it much better. So does the new owner 😃
@@RVwithTito
Tito, so that's your new shower in the new unit, what did you do to fix the old one? Thank you!
@John P No that's the old one. The class A we're in now has a stock glass enclosure. Funny saying old vs new since our new Class A is actually 4 years older than our old class C 😃
@@RVwithTito
Well, I like what you did. I unfortunately don't have a house to do that kind of work; apartments are not conducive to building things. Thanks for the info and the videos, carry on!
Anyone know what the input voltage range on this PWM controller is? I'm contemplating going with 48v LiFePo4 house battery, but still have 12v LCA chassis batteries that want to charge from house battery. Looked at Amazon listing, but didn't see input voltage spec. Will have a 48v to 12v DC to DC converter for house circuits, but that will be a constant supply, not a profiled charger. Would rather not connect this to the 12v side and put extra load on the converter. Would rather it connect direct to battery bus.
It's a 12V or 24V controller
I don't see any reason this wouldn't work with a lead acid to lead acid setup. I keep my RV plugged in at all times...and although I don't have lithium, this setup would keep my chassis battery topped off and balanced with my house batteries...and eliminate the need to keep the chassis battery on a trickle charger for extended periods.
Yes. It should work, just less current flowing. Plus the controller will prevent the chassis from charging the house in case the house get's low.
Just tried it and the charger blew up. Quality is down I think. Will this work with any pwn charger?
Oh. That's crazy. Mine is still going strong. Yes. Any 12V PWM charger should work.
I don't know, this is obvious.....
This is not a good idea. All charge controllers have a max current they can handle, if you exceed that the controller is going to be damaged. So if the starting battery is basically full it will draw little current and you will be OK. However should it be really low when connected you will probably exceed the controllers ratings and destroy i. Since you have it connected all the time this probably wont happen but a fault in the starting battery could cause your house bank to be drained. Its just like having dual batteries in a boat, never have the switch set to both.
The circuit breaker installed by the battery should prevent that from happening. Go with a lower current breaker if you want. Plus you're right. It's always connected so the battery will never get low.