diy solar

diy solar

Renogy DC DC Charger w/ MPPT

boondox said:
Line is for where the power s coming from, load is where it is going. So on the input side, put line going towards the alternator and load to the charger. On the output side, line goes to the charger, load goes to the house battery. Don't worry about charging the start battery, it is very low output and will be fine.
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Thank you boondox.
Maybe you (or someone) can help me with my second question.
The PV negative wire is supposed to be connected to the negative terminal on the Renogy DC-DC/MPPT
That terminal is also connected to the negative bus, which is connected to the chassis (along with the negative lead on everything else in my van).
So the PV negative is always connected to the chassis.
It is not a closed system.
So why can't I just connect PV- to the chassis near the solar panel and avoid pulling a second wire through my whole van?
 
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Hedges said:
Copper is 10x better conductor than steel.
But if chassis is more than 10x greater cross section than the wire, it is lower resistance.
So long as you don't have a bad connection to it. Seal out moisture. Any joints along the path? If so, you don't know they are good electrically, might need to jumper past them.

Electrical Conductivity of Various Metals - Free Knowledge Base- The DUCK Project: information for everyone

wiki.robotz.com wiki.robotz.com
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So assuming I wire the PV- to the chassis at the panel and the PV+ has different resistance or conductivity than the PV- , how could this prevent this particular Renogy (common -) DC-DC/MPPT from properly measuring solar current and feeding appropriate current to the LiFePO4 house battery.
 
Weekendr said:
So assuming I wire the PV- to the chassis at the panel and the PV+ has different resistance or conductivity than the PV- , how could this prevent this particular Renogy (common -) DC-DC/MPPT from properly measuring solar current and feeding appropriate current to the LiFePO4 house battery.
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In a series circuit, current is same everywhere. Kirchhoff's current law.

Excess resistance after SCC in connection to battery would cause voltage drop so battery at lower voltage, but only while moderate current flowing.

Excess resistance in PV to SCC circuit lowers PV input voltage, reduction in power but no other issue unless voltage drops too low. Normally PV string is way above battery voltage, but the Renogy has a fairly Voc limit, not much above battery. So on a hot day voltage drop through excessive resistance could reduce power output further.

Weekendr said:
From what I understand impedance matching can make a difference in certain circuits with a capacitor and an inductor. Is that the case here?
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Not here, that's a special case usually applied to amplifiers and resonators. In most cases, simply lowest wire resistance and lowest power supply impedance delivers the most power.
 
Hedges said:
In a series circuit, current is same everywhere. Kirchhoff's current law.

Excess resistance after SCC in connection to battery would cause voltage drop so battery at lower voltage, but only while moderate current flowing.

Excess resistance in PV to SCC circuit lowers PV input voltage, reduction in power but no other issue unless voltage drops too low. Normally PV string is way above battery voltage, but the Renogy has a fairly Voc limit, not much above battery. So on a hot day voltage drop through excessive resistance could reduce power output further.



Not here, that's a special case usually applied to amplifiers and resonators. In most cases, simply lowest wire resistance and lowest power supply impedance delivers the most power.
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Makes sense to me Hedges. Thank you. I intend to ignore the dire warnings and test my solar with the PV- temporarily connected to the inside of the van roof and see if I get significant voltage drop or any charging issues compared to 10AWG wire right to SCC. If I'm happy I will wire PV- to the outside of the roof permanently.
 
Weekendr said:
Makes sense to me Hedges. Thank you. I intend to ignore the dire warnings and test my solar with the PV- temporarily connected to the inside of the van roof and see if I get significant voltage drop or any charging issues compared to 10AWG wire right to SCC. If I'm happy I will wire PV- to the outside of the roof permanently.
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I've been out in the Mojave, so late getting back to this thread.

Yes, a chassis has greater cross-section. However, the way many modern vehicles are put together they are not truly bonded in all areas. Many manufacturers will designate where you can ground. Now, this is generally about applications that draw a fair amount of current and your solar doesn't. However, I have seen many chassis grounds go bad over the year and be a pain to troubleshoot. And a pain to get to if it is built in. A 10AWG wire is cheap and will never go bad. It's not as if you have to run a pair of 4/0. I would just run a wire and know it will never be a problem.
 
I believe most people have problems with diagnosis when there is a ground problem because most are not even testing the ground circuit.

At least, this is what I found with the 40 years working in the automotive industry. If people only looked at the ground circuit as important as the power, the ground circuit would not have such a bad rap.
 
boondox said:
I've been out in the Mojave, so late getting back to this thread.

Yes, a chassis has greater cross-section. However, the way many modern vehicles are put together they are not truly bonded in all areas. Many manufacturers will designate where you can ground. Now, this is generally about applications that draw a fair amount of current and your solar doesn't. However, I have seen many chassis grounds go bad over the year and be a pain to troubleshoot. And a pain to get to if it is built in. A 10AWG wire is cheap and will never go bad. It's not as if you have to run a pair of 4/0. I would just run a wire and know it will never be a problem.
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Good advice boondox,
I will pull another wire.
 
I discovered another issue with my DCC50s: my alternator does not seem to produce a high enough voltage to charge the LiFePO4 chassis battery properly. It outputs about 13.6V, of which about 13.4V arrive at the battery for charging. Does the DCC50S not have the ability to transform the voltage up? At this voltage, my battery chargers at about 8A (at 70% SOC), so basically very slowly.
I'm not the only one with this problem:
 
If your alternator is only putting out 13.6V it is the problem, not the DCC50S. At that voltage your starter battery isn't being charged properly either.

What gauge wire and what length is the run? Have you measured the alternator output voltage at the starter battery? The DCC50S is not a buck/boost device so it requires a higher input voltage than the target voltage. I would check that the alt is working correctly, that your wiring is sufficient and that your connections are tight. What is the amperage of your alt? Are you checking the voltage at idle?
 
boondox said:
The DCC50S is not a buck/boost device so it requires a higher input voltage than the target voltage.
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Are you sure about this? Maybe there is a communication issue but looking at the specs, it appears that it can change the output voltage depending on what battery you select to charge. Heck, the user settings allow up to 17v. Never seen a car alternator charge that much without some serious problems.

If the solar panels are putting out 24v, then how is it that the charging voltage gets down to 14v?

Sounds like this unit is capable of keeping the battery charged at 14ish v no matter what input voltage there is [within the specs of the unit].
 
Butcher said:
Are you sure about this? Maybe there is a communication issue but looking at the specs, it appears that it can change the output voltage depending on what battery you select to charge. Heck, the user settings allow up to 17v. Never seen a car alternator charge that much without some serious problems.

If the solar panels are putting out 24v, then how is it that the charging voltage gets down to 14v?

Sounds like this unit is capable of keeping the battery charged at 14ish v no matter what input voltage there is [within the specs of the unit].
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No, I'd have to admit I'm not dead sure. I haven't ever gone over the schematic (if one is available) to see the topology. None of the literature I read about the unit mentioned any ability to work from a lower voltage. It would certainly be a more expensive design. I'd also say that being Renogy I wouldn't be shocked if there were settings that can't actually be achieved, or maybe the settings would work with a higher voltage alt. Pity there isn't an easy way to test if the DCC50s would work with a lower input voltage. In any case, if the OP's voltages are what he says they are I still think the problem lies outside the DCC50S. I'm still favoring the alt, wire, connections etc. way more than the DCC50S.
 
Butcher said:
Are you sure about this? Maybe there is a communication issue but looking at the specs, it appears that it can change the output voltage depending on what battery you select to charge. Heck, the user settings allow up to 17v. Never seen a car alternator charge that much without some serious problems.

If the solar panels are putting out 24v, then how is it that the charging voltage gets down to 14v?

Sounds like this unit is capable of keeping the battery charged at 14ish v no matter what input voltage there is [within the specs of the unit].
Click to expand...
Also, in the example of the solar panels, the unit is bucking, not boosting. It can buck for sure. I would love to see a schematic as it seems that the alt and solar inputs share some circuitry, at least when you apply solar the output of the alt side is halved. I suppose it might not be shared components but overall heating issues that require them to halve the output. I guess I just assumed they were using the same silicon but that might not be true.

Is there any DC to DC charger of similar type that is known to buck and boost?
 
I did look at the specs and if it takes a standard alternator voltage and specs out a voltage to keep lithium's happy, then it's got to jump up the voltage somehow. If the users specs allow you to go as high as 17v, then some type of magic is happening inside. In the case of PV, it must be able to lower the voltage too. I'm no expert so I am certain someone that is, can correct me.

Do as you wish, but I would switch up your original statement so it does not appear to be a matter of fact.
 
I suspect the unit is capable of 50a total. So it would be understandable that it could not support 50A from the alternator and 50A from the PV. If that was the case, it would be a 100A unit.

I have read the spec sheet closely and although I could be mistaken, the unit seems to be very capable. The only real issue I can see is the low PV input voltage. It certainly can be worked out, but it does limit which panels will work without that magic smoke coming out.
 
Butcher said:
I did look at the specs and if it takes a standard alternator voltage and specs out a voltage to keep lithium's happy, then it's got to jump up the voltage somehow. If the users specs allow you to go as high as 17v, then some type of magic is happening inside. In he case of PV, it must be able to lower the voltage too.

Do as you wish, but I would switch up your original statement so it does not appear to be a matter of fact.
Click to expand...

Well, one thing that is a fact is that if the alt is only putting out 13.6V then there is a problem. Or if 13.6 is all that appears at the DCC50S that there is a wiring or other issue.
 
Don't just look at the specs. Get the owners manual from the webb and read is closely and critically. Guessing at how it was designed to work is not of much use. WHile I believe friends do not let friends buy RENOGY, if you already bought, read the owners manual. It ain't perfect, but does explain the basic operation of the device. It will charge 50a solar, or 50a alternator, or 25a max solar and 25a solar if both inputs are active.
 
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