60a DC-DC Charger only pulling about 40a

moonlitsouls

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Hey guys

Installed a renogy 60a with a 250amp alternator

When I first turned it on I saw close to 60amps , it started to reduce down rather quickly and seemed to settle around 40-42amp

Any idea why it’s so much less than the rated 60a ?

Thanks
 

Posplayr

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It will depend of course on the type of batteries you are using. For Lead Acid the max charging voltage is about 14.4 volts and if the battery voltage gets anywhere near that it will not accept much current. So the charging current is a function of State of Charge (SOC).

LiFePO will accept nearly anything you throw at them as well in the 13.2-13.4V flat part of the SOC to Voltage range. Above that range, the current will start to tapper.

Now, whether you can accept that full 60 amps or not is going depend not only on SOC but the battery capacity as well because if capacity is large, it is going to take much more current to get through that flat part of the curve.

You should get a realistic estimate of your charging rates based on voltage and state of charge for the programmed voltage parameters in your charger. I won't try and guess what those might be.
 

DJSmiley

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How did you wire it?

should be as close to the secundary battery as possible, with decent wire to handle 60A.

too thin wire between DC-DC and the destination battery will act as a resistor, and limiting the charge current. For 60A and a short distance (<10 ft) Renogy recommends at least 6AWG. I would prefer 5AWG...
Longer runs require even thicker cables
 

kenryan

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Echoing @Posplayr if your batteries are lead acid, run them down to 50% state of charge and then see what your charger puts out. If it puts out 60 amps and then tapers off rather quickly (the smaller the battery, the quicker it will taper) then your charger is operating normally. You are simply experiencing one of the downsides of lead acid battery technology.
 

Porch

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Jan 17, 2021
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Hey guys

Installed a renogy 60a with a 250amp alternator

When I first turned it on I saw close to 60amps , it started to reduce down rather quickly and seemed to settle around 40-42amp

Any idea why it’s so much less than the rated 60a ?

Thanks

Alternator? You are using it to regulate a car alternator? Why?
 

moonlitsouls

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Jan 4, 2021
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How did you wire it?

should be as close to the secundary battery as possible, with decent wire to handle 60A.

too thin wire between DC-DC and the destination battery will act as a resistor, and limiting the charge current. For 60A and a short distance (<10 ft) Renogy recommends at least 6AWG. I would prefer 5AWG...
Longer runs require even thicker cables
Morning , 4 guage wire about 25 feet from the starter battery to the charger, then 4 guage wire about 1 foot from charger to house battery
 

HRTKD

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According to the wire gauge calculator I use, 60 amps over 50' (round trip distance) @ 12v would have a 6.39% voltage drop. That exceeds the 3% threshold that most of us shoot for.

Keep in mind that 60 amps is the max OUTPUT of that charger. It could very well be drawing more than 60 amps to perform the charge.
 

moonlitsouls

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According to the wire gauge calculator I use, 60 amps over 50' (round trip distance) @ 12v would have a 6.39% voltage drop. That exceeds the 3% threshold that most of us shoot for.

Keep in mind that 60 amps is the max OUTPUT of that charger. It could very well be drawing more than 60 amps to perform the charge.
Interesting , ok thanks
 
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According to the wire gauge calculator I use, 60 amps over 50' (round trip distance) @ 12v would have a 6.39% voltage drop. That exceeds the 3% threshold that most of us shoot for.

Keep in mind that 60 amps is the max OUTPUT of that charger. It could very well be drawing more than 60 amps to perform the charge.
I speced 4 awg because @moonlitsouls has a ton of excess alternator capacity.
Its cheaper, easier to run and it consolidated his bom.
60 amps on the output side is ~66 amps on the input side plus a bit to compensate for the voltage drop.
@moonlitsouls what charge parameters are you using?

bulk/absorb voltage?
float voltage?
Charge termination logic?
 

DJSmiley

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According to the wire gauge calculator I use, 60 amps over 50' (round trip distance) @ 12v would have a 6.39% voltage drop. That exceeds the 3% threshold that most of us shoot for.

Keep in mind that 60 amps is the max OUTPUT of that charger. It could very well be drawing more than 60 amps to perform the charge.

Agreed. But the 60A is, as stated, the output current, max 750W for the renogy.

The input current might be higher, depending on the voltage. If the input is 'only' 10V, the booster will still work, but it will draw more from the primary side. At 10V, assuming at max of 750W, that would be 75A or so.

4AWG has no problem to handle that, even 6AWG would do.

Yes, you will have a higher voltage drop, probably more than you've calculated (since you have caluclated at 60A). But from a cable point of view, that can handle it without any issue.

Using proper wire gauges is done for few reasons
- Limit the voltage drop to prevent issues (low-voltage cutoff eg with high inrush currents). Doesn't apply in this case, the DC-DC will compensate for the voltage loss (on the primary side of the DC-DC)
- Prevent overloading of the cables (heating up). Yes, that's true, but to a certain amount. Low voltage cables are generally WAY oversized from a point of heat/current carry capability. 14AGW can run 15A without any issue of heating, but you won't do so because of the voltage drop.
Low voltage = a low drop will still be pretty noticable: 1V drop at a 120V circuit? No-one bothers.. 1V drop at 12V.. that's almost 10% drop.
- Limit cable losses... Voltage drop x current = watts of lost power. If you have situation where every amp counts, it might be worth limiting the cable losses.

For this application 4AWG @ 25FT input, 4AWG@ 1FT to the battery, I don't see any issues. Cables are plenty sufficient.

280Ah LFP should easily handle the 60A charge, assuming it's not already full off course.

- Is the BMS able to handle 60A charge current? Some BMSses have lowerr charge current than their rated discharge current
- Are all connections done properly? Continously 60A requires decent terminals, lugs, nuts and proper torquing. IR thermometer might be usefull, FLIR camera would be awesome.

If you have any other charging options you might check if you're able to push 60A into the battery (Eg 1 or multiple regular AC chargers and solar combined). That would make sure the batteries are accepting 60A charge and you know the issue is somewhere near the DC-DC
 

kenryan

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According to the wire gauge calculator I use, 60 amps over 50' (round trip distance) @ 12v would have a 6.39% voltage drop. That exceeds the 3% threshold that most of us shoot for.

Keep in mind that 60 amps is the max OUTPUT of that charger. It could very well be drawing more than 60 amps to perform the charge.
It seems like the voltage drop might only be relevant in the section of cable that connects the house battery to the B2B charger.

If there is voltage drop in the section that runs from the starter battery to the B2B, that should not be an issue unless the voltage falls below the minimum input voltage for the B2B charger.

It is important, however, that the cables be properly rated with regards to ampacity.
 

Short_Shot

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According to the wire gauge calculator I use, 60 amps over 50' (round trip distance) @ 12v would have a 6.39% voltage drop. That exceeds the 3% threshold that most of us shoot for.

Keep in mind that 60 amps is the max OUTPUT of that charger. It could very well be drawing more than 60 amps to perform the charge.
Yes.


But the output should not be dropping as a result unless the particular unit is *input* limited or monitors the input voltage and limits based on that. I don't know about the Renogy unit specifically.

Ideally it should be a larger feeder though.
 
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