60a DC-DC Charger only pulling about 40a

Posplayr

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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 have done the calculations for voltage drop and including the effect where the input terminal voltage to the charger is below its output voltage. Renogy for example recommends 50% higher input current than the stated output current rating. So if the output is current at say 60A@ 14V then the input will be 90A @ 12V (you would need to go through the numbers).

In my case, I was using a 40A renogy DC-DC, and based on a 3% loss for 16ft of cable I would never want to drop below 12V at the input to the DC-DC. The current draw from the alternate would just get too high.
 

moonlitsouls

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i wonder if the 600W Amplifier for the audio system in the truck may be contributing
 

moonlitsouls

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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 ampacit

im using 4 awg on both sides , the b2b to the house battery is about 1 foot. The cables on the house side were a pair i found already crimped in my tool box , i took them off something else a while back , forgot what. im going to make a new set of cables with some leftover 2awg welding wire i have and see if it makes any difference

i was also considering moving the charger itself into the truck and running the wire inside the cab toward the back of the bed , the battery bank sits right behind the cab of the truck, this would reduce the distance from the vehicle battery to the charger , the distance from the charger to the house battery would increase by about 3 feet to a total of 3-4 feet
 

moonlitsouls

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@moonlitsouls what rpm is the engine at when you only get 40amps output?
pretty much any rpm , i drove it around for a while. saw an average of 40ish amps , some slight fluctuations up as i increased revs but then it would settle back to 40ish , was running between 2-3k rpms on the highway , maybe 1500 on the street
 

smoothJoey

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pretty much any rpm , i drove it around for a while. saw an average of 40ish amps , some slight fluctuations up as i increased revs but then it would settle back to 40ish , was running between 2-3k rpms on the highway , maybe 1500 on the street
check the voltage at the battery with the alternator running but the charger disabled.
repeat test with charger running.
report back.
 

smoothJoey

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if you have an amp clamp I would like to no how much current is on the input wire.
also you never described your charge profile.
 

moonlitsouls

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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?
not home currently but i pulled this from the renogy website , the charge profile settings on the manual i have at home is deff different so i need to take another look at that too , maybe this is a newer model
 

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smoothJoey

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Also do a test with and without your amplifier.
Remind my how big is that new alternator is?
 

smoothJoey

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Since you have a mondo amplifier, have you done the "big three" upgrade?
As in battery.neg to chassis, engine_block.neg to chassis, and battery.pos to alternator.
 

moonlitsouls

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Since you have a mondo amplifier, have you done the "big three" upgrade?
As in battery.neg to chassis, engine_block.neg to chassis, and battery.pos to alternator.
im not sure if the audio installer guy did that when i had it done , i doubt it though. whats a mondo lol?
 

Short_Shot

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Since you have a mondo amplifier, have you done the "big three" upgrade?
As in battery.neg to chassis, engine_block.neg to chassis, and battery.pos to alternator.
600w is mondo?

Hell. Wonder what you'd think of 900rms then.
 

camelCase

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A big three upgrade bumped up the juice going to my camper batteries by over 10 amps, so it's probably worth doing. I have a voltage sensing relay charging lead acid batteries instead of a DC-DC charger, for what that's worth.
 

mikefitz

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My guess, because the input volts to the B2B are low due to volt drops, the unit is having to work hard ( the currents on the input side may be well in excess of 80 amps) and is reaching protective thermal limit, thus causing automatic reduction of power conversion and a lowered output current
This is quite common and can be seen in other B2B units from Sterling and Victron.

A further consideration is that you maybe overloading the alternator and/or the cables from alternator to starter battery and dropping volts along that path.

Mike
 
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smoothJoey

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These are the dip setting for the 2 profiles that I think you should use.
They are the same except the lead acid one has float.

off is up
down is on

lead acid
bulk/absorb=14.4 volts
float=13.2

s1=on
s2=on
s3=on
s4=off
s5=on

lithium
bulk/absorb=14.4 volts
float=NA

s1=off
s2=on
s3=on
s4=on
s5=off
 

moonlitsouls

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My guess, because the input volts to the B2B are low due to volt drops, the unit is having to work hard ( the currents on the input side may be in well in excess of 80 amps) and is reaching protective thermal limit, thus causing automatic reduction of power conversion and a lowered output current
This is quite common and can be seen in other B2B units from Sterling and Victron.

A further consideration is that you maybe overloading the alternator and/or the cables from alternator to starter battery and dropping volts along that path.

Mike
thanks a lot , im going to do some tests , i have a 250a alternator i want to check to see what kind of power its making and so some other tests with the amplifier off and the charger itself off ,
 

Posplayr

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thanks a lot , im going to do some tests , i have a 250a alternator i want to check to see what kind of power its making and so some other tests with the amplifier off and the charger itself off ,
Just so there are no surprises a 250 A rating will probably be rated at 5K+ RPM and will be much lower at idle. Its a saturated curve, that rises quickly with RPM and the levels off after about 3K RPM.
 
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