Renogy DC-DC Test Results-UPDATE 4 (Better!)

[BFL13]

Updates 23 June--new test with Renogy input exposed for voltage readings
Update 25 June more readings
Update 4 - 27 June-- fewer amps with fat wire were noted this time!
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I have the 20 amper Renogy with a 105a alternator in the 2003 truck. The Renogy is in the truck camper near the house battery bank (200AH) and input to the Renogy is via (thin) 7-pin wiring for pos path and neg path.

To run the test I inserted an analogue 60 amp ammeter in the pos path from truck to camper close to where the 7-pin connects to the camper's 7-pin. Camper batts at 50% SOC so lots of time to stay at constant amps in Bulk to run the test.

Truck engine bay heated up during the test (idling with hood up) and truck engine battery voltage came down over time. Noted in test results.

Trimetric monitor for camper batt readings and digital meter for truck input readings

Trimetric showed 12.2v and -00.3a before test. I will give output amps as what the Tri said plus the .3 so 18.8 + .3 = 19.1 Renogy output to battery bank, eg.

Truck and Renogy on at first with 7-pin. Truck batt 13.94 after a few minutes (14.5 start), voltage tapered more as warmed up over 45 minutes.

19.1 amps out at first, then tapering as truck warmed up. (bad--I will have to do some work on that)
When Renogy turned on, output amps ramp up so not instant full amps. (good IMO)

Results:

Truck batt 13.72v, at ammeter 9.88v, 30 amps Tri and 12.8v/ 16.8a tapering amps.

Then 13.63/9.86, 30a and 12.8/15.8,
Then 13.55/9.83, 30a and 12.8/15.2

Renogy unit stayed cool to the touch for whole 45 minute test.

So now the big question is--What happens if you use fatter wiring between truck batt and Renogy compared with the 7-pin????

Using a 25 ft fat wire set of jumper cables (not sure of AWG--ISTR #2 cu-al)

Pos path change only, neg path still via 7-pin:

13.32/11.84 (big jump there!) and Tri showing 12.8/19.1 (big jump in amps there!) still 30 amps on ammeter.

Added neg path half of jumper cables

13.53/13.01 (ha!) 12.9 (battery coming up by now) /19.1 a no tapering.

Checked Renogy output at the unit 13.00v, and Tri says 12.9 so that's ok.

So there you have it for what happens with fatter wire from truck to Renogy No change in Renogy draw still 30 amps, but way better output amps. Adding neg path no change in output, so there is a voltage drop that is not worth improving looks like.

[BFL13]

I changed the Renogy input from 7-pin to by- pass the 7-pin connections in the camper. So input now the same truck 7-pin positive wire but now straight to the Renogy, and a piece of #8 wire from truck frame (by top of bed rail close to the camper) to Renogy neg input terminal.

The actual 7-pin still has the neg wire just no pos pin 4 wire so it runs the signal lights etc, but no charging.

Input voltage was 10.42, now it is 11.28v. No change in output no way to know the draw (assumed still 30 amps)

I have an easy way to disconnect that input as well as the normal 7-pin to take the camper off the truck. I don't see any point in going for fatter wire from truck battery to Renogy unless somebody can say why. ?

[BFL13]

Decided first to check input voltage at the Renogy with things the way I had them before the OP tests. So no ammeter inserted outside on the pos input wire (7-pin) --- did not take this before because no access to Renogy input terminals, now have access.

Got 10.42 volts input, output was 19.4a on Trimetric on battery, meaning 20a at the Renogy termninals allowing for voltage drop. Amps held steady, no tapering this time.

So actually, it works right the way I had it. I blame the additional R of the ammeter and its connections for the lower input voltage during the test, and the tapering, but:

The Renogy specs say it works with 8 -16 volts input and it has a low voltage shut-down at 8 volts input and it did not shut down during the OP test. I had a 1 volt drop from the ammeter to the Renogy input and 9.88 volts at the ammeter, so assume 8.88 at the Renogy.

So it was near the low input limit but not to 8 and shut-down and output amps tapered. It did ok with the test 11.84 (assume 10.84 at Renogy) with the fat wire test.

With this test of as it was set-up, 10.42v input and it worked compared with that assumed 10.84v that worked.

On the "shared negative ground" issue, there is nothing about that in the manual that came with my unit, but there is in the manual you get linked to here:

https://www.renogy.com/content/RNG-DCC1212-20-BC/DCC1212-204060-Manual.pdf

So beats me. I guess the 7-pin neg connection is good enough whatever the electrons are all doing there.

I can add fatter wire to input and improve my installation for output now I have it all exposed, but it appears I don't really need to. I am getting the steady 20a out, no tapering. I don't care what the amps draw is--assume 30 amps as seen on the ammeter.

My owner's manual does not suggest the draw would be less with fatter input wiring. It just says flat out, that with max output amps the draw will be 50% higher. That is what I saw with the test when I switched to fatter wire--still 30 amps.

[BFL13]

Yes, a TT or 5er has a steel bottom frame with wood or al structure on that covered by al skin or fibreglass. So they have a steel bottom frame that they use for "grounding" neg paths.

My camper is all wood with al skin and seems to use the al skin as a neg path. The jacks have the neg voltage too, so they must get that from the skin at the corners where they are attached.

A trailer is connected to the truck via 7-pin and also by the hitch (steel), but the camper only has the 7-pin (6 used-no brakes).

My problem is getting a good wire connection from the truck battery back to the Renogy input terminals that I can disconnect like I can with the 7-pin to take the camper off the truck. Various ways like with Anderson plugs available.

I can go Renogy outpu to camper batts direct (via Trimetric shunt) without much voltage drop, so that part is easy.

I am not clear on what is really needed for the Renogy to have the same "ground" for where the truck battery is "neg grounded" to its frame while the camper battery is "neg grounded" to its "frame" (skin?).

That part is easy in a motor home where the engine and house batts use the same frame.

Anyway, I need to do some more work on my set-up to at least get the Renogy input good enough to allow its output to stay at 20 amps without tapering like it did in the OP the way I have it set up now.

I will try a few things and report back.

[CA_Traveler]

I've having a hard time imagining that a trailer uses the aluminum side for ground for devices which doesn't seem to be a very good ground to me.

Generally 12V and 120V grounds are bounded together and includes all exterior metal, which is a safety factor when on shore power.

But there are no code requirements or enforcement for RVs verus buildings.

[pianotuna]

Hi BFL13,

I would--if I understood your data from the original post--but I don't.

For tables here the only way I've found to 'space' them is to use periods. It requires a * lot * of editing to get the columns to line up.

[BFL13]

The jumper cables are ok, but I agree the clamps can be tricky and need cleaning at times. Note drop along cables was 13.59 down to 13.21 with 30 amps.

I think my camper "frame ground" is not very good where the camper battery is neg connected and then/also to Renogy neg output. There is not much metal in the wood frame, al skin. The clearance and signal lights work right using the al skin.

The Renogy neg input/output is supposed to share the same neg side "ground" truck/camper but they only connect via 7-pin. IMO I need a better way to get the negs to the Renogy. Might be better with a camper that has an al frame. Something to work on anyway.

I did get a voltage reading outside using the pos end of the jumper while it was clamped with the 30 amps flowing and the neg from a camper jack, but the jack is bolted to the wood frame inside the al skin. I can't see where the main neg frame "ground" is behind the power centre, so no idea what it is using for metal.

In a MH you have the same frame for house and engine, but not with a camper or trailer.

I have no idea how a "table" could be used for the OP data. PT could construct one to add here from the data if that would help.

[StirCrazy]

BFL13 wrote:

StirCrazy wrote:
what was the state of charge of the battery you were trying to charge and what type of battery was it? I did see the 12.2, so the other piece of missing info is the actual voltage to the battery, I could care less about the truck battery one, well maybe not thats important just to see how much work the charger is doing to convert the input to the output, but I didnt notice a voltage that was the output while it was only putting out 18 amps... multiply that by that voltage and see if it is at that wattage output max. if it is thats all your going to get. but it could also be a internal battery resistance limiting how much you can take.

Steve

Steve

That was all in the OP. The 19.1 amps on the Trimetric assumed to mean 20 from the Renogy after wire loss. 13.00v at the Renogy with 12.9v at battery. (the 12.9 single decimal point Tri so can't do an Ohm calculation)

20 x 13 = 260w (nominal output given as 250w) We disagree on how that works. When the battery voltage is higher and still accepting the 20 amps , output could be 20 x 14.7 = 294w

____________ Following is not on topic with OP:

Battery type not an issue, but was first time I deep-cycled the pair of 100AH SiO2s from late last year (Covid lack of trips). Used this test as a way to measure their capacity.

Before test was down 115AH and meter showed 12.25v (Tri 12.2) so table says that was between 45-50% SOC. After test, Tri showed down 104AH.
With 55 amp converter set to 14.6,

0955-13.3v, 54.2a, - 104AH (start--low 120v to camper so 54 amps vs 56 with good 120v)
1125-14.2v, 42.5a, - 34.5AH ( missed seeing when amps tapered)
1305-14.5v, 7.8a, - 1.05AH (Supposed to get down to under an amp each at 14.6v --takes a while)
1900, been stuck at 1.4 amps for an hour or so, amps jumping around a little between 1.2 and 1.6, so decided that was it at 0.7a each
AH now plus 16 so that also works where you put more in than took out to get back. Reset the AH to zero.

So the batts have done well on a 13.2v Float (I chose a lower number than spec as a compromise with not Floating them at all) since before Xmas and are maybe a tad above the 200AH. All good.

ya, maybe like PT said , if it was in a table form it would be easier to understand. I dont like the idea of using the jumper cables to do the test, but if that all you got, its all you got. I find they have more internal resistance than using strait wire, maybe because of the ends and stuff I am not sure, but I can tell you I had a bad battery in the HOG and bought a new one and thought I would use my heavy duty jumpers to start it befor I put the battery in incase there was somthing else going on. wouldnt even turn the starter, just click. put the batery in properly, fired up first try..... just weird.

Steve

[BFL13]

Did it with best I can do with ammeter still inserted on pos path otherwise all fat wire except for part of the neg path still 7-pin into camper

Got Renogy input terminals at 12.82v, and still showing 30 amps draw

That's as much as I can do, so there it is whatever it is.

[BFL13]

Got access to Renogy input terminals and re-did the test for the part in question.

With the 7-pin wiring, and the ammeter inserted. With the batts full, load was created by MW on inverter to allow the Renogy to run its full amps

Input--Truck 13.99v, ammeter 10.61v, Renogy input 9.65v--30 amps draw
output about 16 amps (tapering) Renogy output 12.59v, Trimetric 12.4v

With jumper cables from truck batt to ammeter (most of the way to Renogy) using both pos and neg sides--- Load now straight battery recharge-inverter off.

Truck 13.59v,ammeter 13.21v, Renogy input 12.2v, 30 amp draw
Renogy Output 14.38v, Trimetric 14.2v, 19.1a (assumed 20a from Renogy)

Input watts 12.2 x 30 = 366w Output watts 14.38 x 20 = 288w
288/366 = 78.7%

So with 12.2 volts input with fatter wire still have 30 amp draw. Most of the loss from truck to Renogy is from the ammeter to the Renogy as expected with still using the 7-pin for that last part in the camper.

I have to get that part by-passed to have input voltage in the 13s such as would be the case with normal truck input and a small drop from engine batt voltage.

Everyone will still want to know if the input voltage is in the 13s, will the draw still be 30 amps. I still need to insert that ammeter which must have some of that resistance, but we'll see what I can do there.

[BFL13]

StirCrazy wrote:
what was the state of charge of the battery you were trying to charge and what type of battery was it? I did see the 12.2, so the other piece of missing info is the actual voltage to the battery, I could care less about the truck battery one, well maybe not thats important just to see how much work the charger is doing to convert the input to the output, but I didnt notice a voltage that was the output while it was only putting out 18 amps... multiply that by that voltage and see if it is at that wattage output max. if it is thats all your going to get. but it could also be a internal battery resistance limiting how much you can take.

Steve

Steve

That was all in the OP. The 19.1 amps on the Trimetric assumed to mean 20 from the Renogy after wire loss. 13.00v at the Renogy with 12.9v at battery. (the 12.9 single decimal point Tri so can't do an Ohm calculation)

20 x 13 = 260w (nominal output given as 250w) We disagree on how that works. When the battery voltage is higher and still accepting the 20 amps , output could be 20 x 14.7 = 294w

____________ Following is not on topic with OP:

Battery type not an issue, but was first time I deep-cycled the pair of 100AH SiO2s from late last year (Covid lack of trips). Used this test as a way to measure their capacity.

Before test was down 115AH and meter showed 12.25v (Tri 12.2) so table says that was between 45-50% SOC. After test, Tri showed down 104AH.
With 55 amp converter set to 14.6,

0955-13.3v, 54.2a, - 104AH (start--low 120v to camper so 54 amps vs 56 with good 120v)
1125-14.2v, 42.5a, - 34.5AH ( missed seeing when amps tapered)
1305-14.5v, 7.8a, - 1.05AH (Supposed to get down to under an amp each at 14.6v --takes a while)
1900, been stuck at 1.4 amps for an hour or so, amps jumping around a little between 1.2 and 1.6, so decided that was it at 0.7a each
AH now plus 16 so that also works where you put more in than took out to get back. Reset the AH to zero.

So the batts have done well on a 13.2v Float (I chose a lower number than spec as a compromise with not Floating them at all) since before Xmas and are maybe a tad above the 200AH. All good.

[theoldwizard1]

BFL13 wrote:

One threat was if a low camper battery bank caused the input amps to go way high and overtask the alternator.

The fuse on the B+ wire protects both the wire AND the alternator.

[StirCrazy]

what was the state of charge of the battery you were trying to charge and what type of battery was it? I did see the 12.2, so the other piece of missing info is the actual voltage to the battery, I could care less about the truck battery one, well maybe not thats important just to see how much work the charger is doing to convert the input to the output, but I didnt notice a voltage that was the output while it was only putting out 18 amps... multiply that by that voltage and see if it is at that wattage output max. if it is thats all your going to get. but it could also be a internal battery resistance limiting how much you can take.

Steve

Steve

[theoldwizard1]

BFL13 wrote:

So the Renogy with 7-pin input does way better than the 7-pin by itself. However, the Renogy amps should hold at its 20 amp rating during the Bulk stage of charging. Mine only did that with the fatter wiring as described.

I still would contact Renogy with your data before going through the hassle of installing a larger charge wire.

[BFL13]

Will pick which wire to use for input when I get to that. 🙂

The mystery is why it still was pulling 30 amps when it ought to have been fewer amps draw with the fatter wire. Suggestion was it might be current limited for draw. Might be.

One threat was if a low camper battery bank caused the input amps to go way high and overtask the alternator. Fatter wire was thought to help with that if there is no current limit on input.

My test has none of that info, so somebody else can deal with that.

[NRALIFR]

I believe it was on the FAQ page of the Redarc site where I read that the number one reason for poor performance complaints on their DC-DC chargers was not using the recommended wire gauge for the length of the circuit.

What’s the recommended gauge for your install? What’s the gauge of the wire your using? What gauge are you planning to use to improve it?

:):)