Question 1

I have a 130amp alternator. will the 60amp renogy dcdc charger be too large and damage the alternator? how about at idle for up to 1 hour?

Accepted Answer

I just talked to tech support at Renogy about this. For alternators of less than 160 amps use the 20 amp charger, up to 180 amp alternator use the 40 amp, and for 200 amp alternators and above the 60 amp alternator can be used. My alternator is 220 amps, but I am going to take the safe route and use the 40 amp charger. I doubt that it is a good idea to charge too much at idle.

Question 2

What size alternator do you need for this to work

Accepted Answer

For an alternator of 150A and under a 20A charger is recommended I use the 20A with a150A alternator on a 2015 transit250 it charges 210A/hours batteries in les than 2 days of driving. If you need charging done faster I recommend replacing your alternator to 250A for a 60A charger.

Question 3

Where does the D+ wire get mounted to?  I can interpret the instructions in three different ways, so I am curious what you all have done.

Accepted Answer

D+ is a 12v trigger for your charger other words it lets your charger know that there is 12v present from the main battery so it can start charging. If you have access to your alternator is the 12v+ main wire where D+ needs to go if you don’t have access to the alternator find a spare unused circuit in your fuse box one that is hot only when the engine is running. If none of this makes sense I suggest finding an installer otherwise you can fry your wiring

Question 4

At 40A, I'll have to run the engine for 2.5 hours to charge a 100 amp hour battery (from completely drained). Correct?

Accepted Answer

In principle yes, however, it will probably take twice that long for a "full charge." From the discharged state it will charge at 40 amps but it will reduce the charge rate for best charging and battery life.  You don't want to run from full to empty and back every day.  I have your configuration (100 amp hour battery and 40 amp charger). I drive 40 miles every day and it is enough to charge the battery for my CPAP and other medical devices for the night.

ASIN	B07Q5VYPCF
Amperage	20 Amps
Battery Charge Time	2.5 Hours
Best Sellers Rank	#15,214 in Automotive ( See Top 100 in Automotive ) #5,023 in Automobile Accessories
Brand	Renogy
Built-In Media	charge controller
Color	Black/Blue
Colour	Black/Blue
Current Rating	20 Amps
Customer Reviews	4.2 out of 5 stars 996 Reviews
Global Trade Identification Number	00816360029991
Input Voltage	12 Volts
Item Dimensions D x W x H	17.5D x 21.1W x 6.9H centimeters
Item Type Name	Using Multi-Stage Charging in RVs, Commercial Vehicles, Boats, Yachts, 20A
Item Weight	2.93 Pounds
Item weight	2.93 Pounds
Manufacturer	Renogy
Mfr Part Number	REN-DCC1212-20
Model Number	12V 20A DC to DC
Output Voltage	12 Volts (DC)
Output voltage	12 Volts (DC)
Product dimensions	17.5D x 21.1W x 6.9H centimeters
Specification Met	CE, RoHS
Specification met	CE, RoHS
UPC	816360029991

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

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