Renogy DC-DC charger 40a w/o MPPT solar: questions / reviews???

[Impatient]

The “new” or at least “newer” DC-DC charger (RBC40D1U-US) sounds perfect for my need, except per the “1-star” and “3-Star” reviews, it doesn’t shut off appropriately, and drains the starter battery. Does anyone have experience with this particular model working properly or improperly? I sat “on hold” yesterday with Renogy support for 1.5 hr total, even though I started at 2nd in queue, then moved to 1st for about 45 min of that, so gave up. I would be using it in a 2015 Ford Transit, which I think has conventional alternator, and an SOK 206. I already have a Victron MPPT, but don’t like the older Orion, and new Orion XS kinda pricey. Most all the combined DC-DC / solar controllers have too low a solar voltage limit for my hi-voltage panel, so they don’t cut it either.

Amazon.com

12V 40A DC to DC Battery Charger

Renogy offers reliable and innovative solar panels, inverters, lithium batteries, and solar charge controller for off-grid solar systems. Shop confidently with premium-quality products, expert guidance, and outstanding customer care to achieve your energy goals with ease.

www.renogy.com

 

[Sellier_bellot]

Renogy is risky in general. Customer support is a joke, I hear horror stories on warranty claims.

That being said, I bought the 50A RBC2125DS-21W dual solar/DC alternator unit. I'm able to get 50 straight out of the Alternator or drop it to 40A, 30A etc. it's configurable. I verified at full SOC the system drops out of constant current, the current drops at constant voltage. The solar input is disconnected as I don't have panels on my Sprinter van yet.

Sorry, I can't speak to your model. Check this one out and see if you can return yours?

 

[HRTKD]

The Orion XS is a great unit. You can throttle it down to work with the alternator and wiring you have now. Later, when you have better wiring and/or a bigger alternator, you can crank it up to the full 50 amps.

 

[RV8R]

I’m not a Renogy fan, but what is perfect about this $170 unit other than the price ?

In terms of this Renogy unit not shutting off & draining the starter battery, that can be easily overcome with a manual switch & remembering to turn the switch off when not in use.

I have a Kisae 1250 in my van & have manual switches on both positive sides if this DC2DC charger (House & Starter) batteries;

DMT1250 – Kisae Technology Inc

I don’t have a Victron Orion XS, but hear they are also very good. The Older Orions had “heating up issues”, but I believe Victron has fixed that in the new XS models.

On Another Note; It is a good idea to figure out what “spare” power / energy you can expect from your alternator. I have a 2021 Promaster & can expect usually at least 50amps @ 14v outta my alternator to my Kisae 1250 (which is user programable for voltage & amperage). User programable is very important IMO for DC2DC chargers.

 

[Impatient]

First, THANKS FOR REPLIES!

Price is a big factor, but not frying things is an even bigger concern.

QUESTION: wire size: I know I can’t drive the XS, or any 40a or 50a charger, anywhere near full power through my existing wiring. But if I were to limit the Orion XS (or Kisae, or Renogy for that matter) to 20-25a output, would an 8ga wire on the input side cause any issue, being so “small?” It’s 13’-14’ long. I’m using the van chassis for return “cable.” “Non-isolated” fashion for you Victron folks.

today my setup (which includes a Victron Smart Solar MPPT 100/20 and a CTEK d250s (non-lithium) DC-DC, with wiring/switching/fusing) is “evidently” sufficient for 20a. There is a 30a switch and fuse on the starter battery side of that 13’-14’ 8 ga cable…so input power can be shut off to the DC-DC charger. There is another 30a switch near the house batteries, that controls which controller goes to which house battery bank. Unless I do some major revamp, both switches would remain in the path of this potential new DC-DC charger. Hence, I need to keep the amperage down. Nominally 12v.

The CTEK senses voltage, and at engine start-up, after a brief delay starts charging. When engine is turned off, it does wait a few moments before turning off again (back to the original concern about the Renogy). I am trying to avoid having to use a d+ signal wire, although I suppose that could eliminate one of the switches (on the starter battery end). Plus, if the house battery is full, it will “trickle-charge” the starter battery. But I really think the CTEK works correctly, or at least as correctly as a flooded-battery-era charger can.

 

[HRTKD]

8 awg is too small if you pushed the 30 amps the switch/fuse is capable of. Here's the calculation from the Bay Marine Supply calculator. If you limited the input into the DC-DC charger to 20 amps it would be 3.02% voltage drop. So just a smidge over the 3% limit with like to see.

 

[Stircrazy]

wow a lot of comments against renogy from people who it is obvious haven't had one or haven't read the owners manual for the dc to dc.
1 you can cut the output in half with settings on the dc to dc so my 20 amp can be set to 10 amp max out put and same as the 40 it can be set to 20 amp. this I didn't know until I read the owners manual. second I have never had a issue in the last 7 years with my solar controllers or over the last 2 years with my dc to dc or my inverter, the issues I did see before were related to batteries and solar panels but who knows.. I did email renogy a few times with questions and they got right back to me so I don't know where the customer service issues come from. as for they keep running and cant throttle down.. that is true and not true, depends how you hook them up. the basic way is just to run a line to a alternator hot output so when your truck starts so does it, but anyone with half a brain will look at this and figure they can put a switch in that line to control when it is running and not. I have mine on a upfitter switch in my truck that is only hot when the engine is running. this lets me leave the button on when I am camping and if I am getting bad solar days and I need a few AH added to the battery I just use the remote start from inside the camper. that only works for 1/2 an hour so eventually I have to get up and just start the truck and let it run for a bit, but you get the idea. normally the button is off as the solar keeps everything charged right up and the dc to dc is just a back up.

 

[wme]

FWIW there are at least 8 different brand DC to DC on Ebay, from 45.95 to 245.00. Utube reviews on many

 

[Impatient]

8 awg is too small if you pushed the 30 amps the switch/fuse is capable of. Here's the calculation from the Bay Marine Supply calculator. If you limited the input into the DC-DC charger to 20 amps it would be 3.02% voltage drop. So just a smidge over the 3% limit with like to see.

View attachment 277219

This hits on one of my fundamental wiring questions: if I use the chassis as the return (negative “wire”), how does that affect this calculation? What “gauge” is the chassis? You used “round trip” distance (which I guess would be appropriate if both directions were via this wire size (isolated vs non-isolated). But in addition to the equivalent wire size of the chassis issue, the return distance is also shorter, as the path doesn’t need to follow the same path as the wire clinging to the outer walls of the van….more like a hypotenuse of a right-angle triangle.

 

[HRTKD]

If you don't know how to calculate the equivalent gauge cable for the chassis, you might as well take the worst case scenario, which is running wire both directions. Don't guess.

 

[RV8R]

Hi @Impatient

A 2015 Ford Transit ,,, I have little knowledge, but I assume many on this Transit forum do;

https://www.fordtransitusaforum.com/whats-new/posts/

I have a 2021 Ram Promaster & sized my #1 AWG wire (with return chassis negative) original for a Cyrix230. I wanted very little “Voltage Drop” & achieved that with the #1 AWG & chassis. Now is it somewhat irrelevant with my DC2DC Kisae 1250. The Promaster chassis had very little resistance & a huge mass ,,, Albeit steel. However, the Alternator & Starter Battery both use the chassis to connect ,,, so there is that. There is theory & real life ,,, but I believe your chassis would function as a substantial wire.

The Transits have CPP1 & CPP2 as far as I know for the positive connection cable;

https://www.fordtransitusaforum.com/threads/alternator-charging-from-2022-awd-transit-148-wb-not-the-extended-length-med-roof.96964/

@HarryN has Transit experience. He is also on that Transit forum as are other very experienced members. I really think it would be in your best place interest to join & enquirer there.

 

[Impatient]

I’m also trying to figure out what the real effect of a voltage drop is between starter battery/alternator and a DC-DC charger. Assuming enough voltage exists to keep the charger from going to sleep, is the downside merely less amperage on the output side of the charger? I could also relocate the Dc-DC charger: shortening the distance from the source (alternator/starting battery) but that would lengthen the distance to the house battery…which I had assumed was the connection more sensitive to voltage drop.

 

[brainbone]

I’m also trying to figure out what the real effect of a voltage drop is between starter battery/alternator and a DC-DC charger.

The voltage is dropping because the too small of wire is being heated. The real effect is hot wires. Something you certainly want to avoid. Don't cut corners here. Bite the bullet and run larger cable.

Edit: If you put the DC to DC converter on the far end, it'll likely draw even more than 30 amps as the voltage drops and it tries to boost it for charging, heating the wire even more.

 

[RV8R]

I’m also trying to figure out what the real effect of a voltage drop is between starter battery/alternator and a DC-DC charger. Assuming enough voltage exists to keep the charger from going to sleep, is the downside merely less amperage on the output side of the charger? I could also relocate the Dc-DC charger: shortening the distance from the source (alternator/starting battery) but that would lengthen the distance to the house battery…which I had assumed was the connection more sensitive to voltage drop.

I have a Kisae 1250 ,,, Kisae told me to place the DC2DC close to the house battery ,,, this makes sense as you want the voltage accurate for the battery you are charging .

So if you can just run large wire from your starter battery.

 

[Stircrazy]

I have a Kisae 1250 ,,, Kisae told me to place the DC2DC close to the house battery ,,, this makes sense as you want the voltage accurate for the battery you are charging .

So if you can just run large wire from your starter battery.

yup the proper placement for a dc to dc is right at the batteries you are trying to charge. so you need one for each RV if you have more than one.