Renogy 12V 20A DC to DC On-Board Battery Charger for Flooded, Gel, AGM, and Lithium, Using Multi-Stage Charging in RVs, Commercial Vehicles, Boats, Yachts, 20A

9 Months Later and Going Strong
Installed a 40A Renogy B-to-B charger in my A-Frame pop-up camper last year after upgrading the camper’s “house” battery to a Lossigy 200ah LiFePO4 (Lithium-Iron-Phosphate) battery. Reason? The standard “battery charge” lead from most tow vehicles never supply more than 8 amps, which meant we had to drive for at least 12 hours to restore even 50% of the battery’s capacity! (Ok, you may want to skip this paragraph unless your tow vehicle is a hybrid.) So, our favorite mule, a 2016 Toyota Highlander Hybrid, raised some concerns because we would be tapping the vehicle’s 288V NiMH hybrid battery instead of an alternator to supply the charge current. But, this car does have it’s own 12V AGM accessory battery which receives its charge from the hybrid battery via step-down converter. So before getting too far into this project I sampled the current flow in and out of the 12V AGM battery with the ignition on and found it often hit 60 amps or more when the AGM battery needed charging and accessories are on. This is generally more than enough to supply the 40A DC-to-DC charger as long as the AGM battery is in good shape! Whether or not your tow vehicle is a hybrid, the Renogy unit incorporates some useful features for protecting the vehicle’s 12Volt system, and in this regard I can’t say enough good things about the LC (Limit Current) feature. What does this do? It allows the user to set the current draw at either 20A or 40A. Why is this important? Because when towing, especially at night with all running lights on, there is potential for sudden high current demand from the vehicle’s 12 volt electronics. So, to minimize any risks of over-taxing the vehicle I leave the 20A LC feature enabled while towing. In five hours of driving, 20A of current will provide about 100ah or 50% of the 200ah battery’s full charge – usually more than enough! But what if we’re camped somewhere for a few days and need additional charging? Simply connect the camper’s umbilicals to the parked tow vehicle, turn off AC and all the 12V accessories, fire it up, disable the LC, and . . . get 40 amps! (See attached photos: one shows the DC-to-DC charger unit mounted on the forward bulkhead under our dinette table alongside a Renogy solar controller, and the other is of locking push-button illuminated switches I mounted on an interior wall panel. The buttons are wired for switching the DC-to-DC charger on/off, and for enabling/disabling Current Limiting or LC.) Btw: I priced DC-to-DC chargers from other manufacturers and found the only units with the LC feature are in the $400+ range. Couple of things to be mindful of, no matter what your configuration:1. Several reviewers have mentioned the importance of properly wiring the D+ lead so that the DC-to-DC charger will shut off when tow vehicle’s engine is turned off. This is particularly important if you’re tapping the vehicle’s 12V battery for charging. I chose the cigarette lighter (aka: 12V Port) circuit for this since it is only active when the vehicle is actually on. (Some have chosen the running lights circuit, but it’s just too darn easy to forget to turn off lights, especially when parked somewhere during daytime.)2. To avoid significant current loss and less than-optimal-charging, it’s very important to use heavy gauge, minimum resistance wire (I chose 6AWG Marine Duplex) for the circuits that will be carrying the actual charge current. Expensive, but worth it. On the other hand, the signaling circuits (D+ and LC) can generally be a much lighter 16AWG.3. Carefully follow Renogy’s instructions for installing the unit – particularly with regard to fusing and wire gauges.Update: This unit has been functioning perfectly for over a year and thousands of miles. And the gas/electric hybrid tow vehicle turns out to have one added plus with a battery-to-battery charger, especially while boondocking. Reason: When parked with the ignition on, the hybrid battery can deliver a continuous 40A through the DC-DC Charger without the ICE (Internal Combustion Engine) firing up for more than 15 minutes out of every hour! Certainly an efficient (and quiet) alternative to hauling a generator around. (Of course it works best if the engine is already warm and the hybrid battery is fully charged, like, right after returning to camp from an excursion to a favorite fishing hole.)

Great for charging your RV from the truck
Yes it works well. Follow the directions. Don’t cut corners. Don’t burn your truck or RV down because you want to save $5. Get the good stuff.

Producto de buena Calidad es de gran apoyo ya que aparte de cargar tu batería externa si estas usando en ese momento el inversor suministra los 40 amperes adicionales al inversor por lo que no salen de la bateria dicha corriente por lo que mantiene tu batería cargada más tiempo a diferencia si estuviera apagado dicho cargador.

Bon produit pour mon besoin

Works exactly as advertised.I use this unit to charge my house bank of batteries on my boat.I have added a two minute delay to allow the starter battery to get some charge before the full 40 amps from this charger kicks in. With my motor below 1100 RPM, this sucks juice from the start battery and the alternator. Above 1100 RPM and they both charge at the same time.Someone asked why there is an amp cutting switch. E.g. this unit can be triggered to cut the output to 20 amps from the full 40 amps. To me, this would be valuable if you are doing a lot of idling. Depending on how you have it wired and how many amps your alternator kicks out, cutting the amps would prevent you draining your start battery by feeding this charger while idling. Once you trigger the amp cut it does not stop until you restart the charger, you must shut it down to get it to reset that feature.Solid piece of hardware, good documentation.I did a long trip with it and watched it cycle through bulk, the absorbtion stage, then go into float mode, it does it all smoothly and managed 4 large 135 AMP hour batteries at once with no difficulty. It modified the time for the stages based on the starting state of charge and the loads placed on the system while running, totally dynamic and automatic.