Diode needed for 48v to 12v converter?

[TheDude130]

I am putting together a 48v DIY pack with a Growatt inverter/charger for my towable RV. I plan to use something like this to handle the 12v loads: https://www.amazon.com/dp/B07ML5ZML2/ref=cm_sw_em_r_mt_dp_7SS3443VRMKYC9B77DX1

My question is: should I not put a diode on the the step down converter output to prevent the tow vehicle from backfeeding into this converter? The tow vehicle will wind up being higher voltage than 12v for sure when running, so this seems logical. Or are these devices generally already protected against this scenario? I noticed this was not really covered in Will's design, but I wasn't sure if there was a reason.

 

[chrisski]

I needed a larger than 50 amp to power my DC jacks so I got the Victron Orion.

Amazon.com

should I not put a diode on the the step down converter output to prevent the tow vehicle from backfeeding into this converter?

I don't have a good answer. Look at Post 59 on this link:

https://diysolarforum.com/threads/24-vdc-and-12-vdc-brakes-in-fifth-wheel.10915/page-3

I think this is the back-feeding you were talking about and in this instance may have been the source of the fire. Could have been that converter had a duty cycle that got exceeded where on for so much per hour than off the rest. I am not sure.

I don't really thing you're looking at back feeding here with a diode. To me back feeding is Polarity Reversal. What you're trying to prevent is a huge amount of current flowing in trying to charge the battery, which I don't think a diode will protect from. For charging from the tow vehicle this solution would be buying a DC to DC converter to charge a lithium battery from an alternator so the lithium battery does not burn up the alternator.

I'm wondering if there is something that should be done, even disconnecting the 12 volt from the trailer pin. I do not need the power from the 12 pin because my trailer makes plenty, but I'm not sure how that will effect the electronic brakes or even outside brake an turn lighting.

In my case, I removed the 12 volt battery, so I don't think this will be an issue, but it goes back to post #59 in the thread linked above.

 

[mikefitz]

I would not worry about back feed. What I would worry about is the reliability of such units.
Consider,

Orion-Tr DC-DC Converters Isolated - Victron Energy

Provide a stable DC output voltage using the, easy to install, Orion DC-DC Inverter from Victron Energy. Find a dealer near you.

www.victronenergy.com

If you have heavy consumers like levelling rams/jacks, having a 12v lead battery may be useful.

You may find there are more equipment options with a 24 volt system.

Mike

 

[Don B. Cilly]

No. I mean, it doesn't say so... but if the efficiency is "96%" it has to be PWM.
So it's got enough diodes (mosfets) on the output to prevent any "backfeed".

Thing is... it's described as "Synchronization Rectification Technology": Probably meaning "active rectification". It's Chinese.
In my experience, especially on Amazon, Alibanggood, etc. you want a 30A thing, if it's 中国人, get a 90A one. :·)

 

[chrisski]

If you have heavy consumers like levelling rams/jacks, having a 12v lead battery may be useful.

Although called a DC to DC converter, those isolated Orion can be used as a charger. The non-isolated one I got can't.

Can't say I know anyone who has removed the battery from a fifth wheel. Although my battery monitor says 50 amps and less for the jacks, I still am not sure if there is some huge surge for these motors that won't work with the 70 amp Orion. I can put more Orion's in parallel, but may put the battery back in if its an issue. Will likely be Beginning of December now when my 24 volt upgrade is done.

 

[RCinFLA]

Don't need a diode but should put a fuse and a switch to disconnect it from 48v battery when not in use. Keep in mind it will draw some idle current even with no output load on it.

 

[TheDude130]

Sounds like the consensus is probably no diode needed to protect the converter from power coming into the input side from the tow vehicle.

Another question for anyone familiar with these types of units is are they generally parallel capable? I would think so. I don't have any large loads like jacks, but I do have a DC chest fridge. It still has a pretty small startup load. However, I was thinking as cheap as these things are, I might just run two in parallel for more headroom and redundancy. The other option is just to pick up this and forget about it, but there quite a price jump: https://www.amazon.com/Victron-Orion-TR-DC-DC-Converter-Isolated/dp/B07DQ5H3T2?th=1

 

[Smokin]

When the switching mosfet fails inside the Buck converter they short and send 48 volts out to what should be 12 volts. This blows up everything attached to it that is turned on. And maybe some things that are turned off. I would never use one unless you are OK with that senero.
One proper way to do it is leave the 12 volt system in place and use a buck converter that has current limiter to charge the 12 battery. This link will need a small value fuse between the buck and battery.
Some times it is ok to use these 48 to 12 volt converters to run light loads like 12 volt led lights on golf carts and a radio. But the threat never goes away that you will experence a voltage spike.

 

[chrisski]

. It still has a pretty small startup load. However, I was thinking as cheap as these things are, I might just run two in parallel for more headroom and redundancy.

I would only parallel with what is in the manual. If its not, then I would not parallel. In general most generators or DC to DC converters that I've seen are designed to parallel up to a certain number.

 

[TheDude130]

Just be clear, I have no plans for a 12V battery. This is a small Intech camper with light 12V loads: fan, stereo, led lights, USB chargers, and a small 12v fridge. No water pump, jacks, or any other high draw DC loads. I think from the sound of it, I'd be best just springing for the Victron. There's a reason you pay a premium. Their stuff tends to be pretty bulletproof. Plus it has a simple remote switch connection and adjustable voltage output, which would be handy if I ever do wind up throwing in a 12v battery.

 

[Lt.Dan]

Although called a DC to DC converter, those isolated Orion can be used as a charger. The non-isolated one I got can't.

Can't say I know anyone who has removed the battery from a fifth wheel. Although my battery monitor says 50 amps and less for the jacks, I still am not sure if there is some huge surge for these motors that won't work with the 70 amp Orion. I can put more Orion's in parallel, but may put the battery back in if its an issue. Will likely be Beginning of December now when my 24 volt upgrade is done.

I got rid of my 12v battery entirely, and run a 100a 48v to 12v converter. It runs my leveling system that has a huge spike and a constant 60a when running. It doesn't do it well, but it does it. I plan on getting a 150a 13.8v converter to make it better.

I am in the boat that I did not want my tow vehicle putting a higher voltage to the system, so I made sure my truck did not have the charging fuse installed. It works great.

 

[time2roll]

Make sure it will operate the emergency brake system.

 

[chrisski]

I got rid of my 12v battery entirely, and run a 100a 48v to 12v converter. It runs my leveling system that has a huge spike and a constant 60a when running. It doesn't do it well, but it does it. I plan on getting a 150a 13.8v converter to make it better.

Thanks for sharing. I hope the 70 amp works with mine. I normally see 35 amps when leveling, but I have seen 50 amps. It’s a 4 point leveling system on a two axle trailer.

Bad thing is the RV is in the repair shop now after a tire blow out caused a lot of damage, so that is my big hold up on getting this build complete.

 

[Lt.Dan]

Make sure it will operate the emergency brake system.

That's a good idea that I haven't thought of. I'll jack up one tire, pull the breakaway plug and see if the brakes lock.

 

[time2roll]

Generally need three amps per wheel. Maybe more if RV has electric over hydraulic discs.

 

[Pappion]

I used an automotive relay to isolate my 13.8v boost (12v input) when the tow vehicle is not providing power to it.
Also used fuses on input and output, because I don't trust Chinese electronics. Yea, it looks similar to your finned brick.

new travel trailer:
I retained the 12v lead acid battery for the emergency braking and the jack, as it has a better cold temperature range.
Prior experience after one Thanksgiving in Ohio was trying to outrun a 10f cold front sweeping the nation.
Also don't want an accident investigator saying its my fault for modifying the emergency brake system.

The rest runs off my 12v LiFeP04. I have a Bat1 - Batt2 - Both switch.
I have not bothered with battery heating yet. It's warm enough when the furnace is running. Which doesn't run when I am traveling.

 

[Zwy]

I am putting together a 48v DIY pack with a Growatt inverter/charger for my towable RV. I plan to use something like this to handle the 12v loads: https://www.amazon.com/dp/B07ML5ZML2/ref=cm_sw_em_r_mt_dp_7SS3443VRMKYC9B77DX1

My question is: should I not put a diode on the the step down converter output to prevent the tow vehicle from backfeeding into this converter? The tow vehicle will wind up being higher voltage than 12v for sure when running, so this seems logical. Or are these devices generally already protected against this scenario? I noticed this was not really covered in Will's design, but I wasn't sure if there was a reason.

When I setup my system, I separated the 12v circuits from the original power center and installed a fuse panel with power from the buck converter. The only circuit on the power center is the power jacks for loading and unloading the truck camper and that circuit is connected to the 7 pin and thus the truck. I did have a small 15 AH AGM battery around that I put in there just for some spike absorption when running the power jacks. Shown in photos is the new 12v fuse panel and the buck converter with it's breaker installed behind the panel. Old power center converter now has a switch to turn off AC power to it, I just flip it on when running the power jacks.

 

[eXodus]

I retained the 12v lead acid battery for the emergency braking and the jack, as it has a better cold temperature range.
Prior experience after one Thanksgiving in Ohio was trying to outrun a 10f cold front sweeping the nation.

same here. Just keep the 12V battery and turn on the 120V to 12V charger. Much less work.

should I not put a diode on the the step down converter output to prevent the tow vehicle from backfeeding into this converter? The tow vehicle will wind up being higher voltage than 12v for sure when running, so this seems logical

you don't need a diode. It's just multiple power sources parallel. The buck converter should not take any power in, but it could be poorly designed internally and a diode is a wise precaution.

but like I mentioned before - keeping the 12V system of the RV is very easy and no extra expense.