Renogy DC DC Charger w/ MPPT

[rubberlegs]

I rarely ever lean towards lighter duty. I would rather see a item work at 60% to give you your needs vs 100%. Means nothing and it's all mental, I get it, but it still does not change my mine.

I was thinking the same, perhaps from a different viewpoint. The 30A would produce less heat in our camper, and charge the battery slower, and put fewer amps in the wires. The "black box" appears to be the same as the 50A (same cooling fins), so that's why I think it would run cooler. However, I have no idea what the components are, and whether it's best to be kind to the charge controller or the battery. Certainly the solar panels are gentle on all the downstream components, since we'd only have 200W. It's the alternator side that's the question.

In the aerospace industry, we'd usually do the minimum to save weight. So I'm used to not overdesigning things.

 

[dirt diggler]

I've a question about this DC-DC charger, and I'm sorry if its already been asked and answered before, but there's over 40 pages in this thread.

Can you connect a AC-DC charger to the inputs of this so it can be used from charging/battery management?

I'd like to attach an old laptop or battery charger or something similar, and use it to not only charge the battery, but also power the 12V system while shore power is available. Is this possible? (I realise you'd probably have to pull D+ high??)

Thanks

I have an AC charger when on shore power, it charges the starter battery (same thing as you are suggesting? ) the DCC50s just sees voltage so it charges the house battery, i do this as my AC charger is FLA and i have LiFeP04 as a house battery so the DCC does all the converting to a propper charge profile, i'm not sure a laptop charger will have enough "ooomph" to keep up though, mine is a 30A and it seems be ok the 2 or 3 times i've used it.

 

[dirt diggler]

I rarely ever lean towards lighter duty. I would rather see a item work at 60% to give you your needs vs 100%. Means nothing and it's all mental, I get it, but it still does not change my mine.

When i was a (good) few years younger i used to instal sound systems in cars and the old boy i worked with allways said never run anything at more than 75% for long, be it mechanical or electronic, i allways followed that advice, i hope it helped me over the years, he's gone now so i can't moan at him !

 

[EnsignR]

I have an AC charger when on shore power, it charges the starter battery (same thing as you are suggesting? ) the DCC50s just sees voltage so it charges the house battery, i do this as my AC charger is FLA and i have LiFeP04 as a house battery so the DCC does all the converting to a propper charge profile, i'm not sure a laptop charger will have enough "ooomph" to keep up though, mine is a 30A and it seems be ok the 2 or 3 times i've used it.

Thanks for the reply.

Did you need to do anything with the D+ pin?

I'm currently using an AC battery charger to charge the (current) single AGM battery I have before building a multi-battery system but you need to set the battery type each time you turn it on which would be a pain if it were permanently collected and stowed away with the batteries.

 

[rubberlegs]

the old boy i worked with allways said never run anything at more than 75% for long

Won't a 50A run at 50A, and a 30A run at 30A, if the energy is available (from alternator when solar disconnected, and my solar would only produce 15A)? Thus they both run at 100%.

 

[brb58]

I was thinking the same, perhaps from a different viewpoint. The 30A would produce less heat in our camper, and charge the battery slower, and put fewer amps in the wires. The "black box" appears to be the same as the 50A (same cooling fins), so that's why I think it would run cooler. However, I have no idea what the components are, and whether it's best to be kind to the charge controller or the battery. Certainly the solar panels are gentle on all the downstream components, since we'd only have 200W. It's the alternator side that's the question.

In the aerospace industry, we'd usually do the minimum to save weight. So I'm used to not overdesigning things.

Most MPPT solar controllers are at least 95% efficient. The amount of heat put off is therefore minimal.

 

[Butcher]

I look at stuff like that as it can run 'up to' 50A or 'up to' 30A.

When it comes to heat being generated, I like knowing watts. For some reason, I can wrap my head around watts as heat vs amps.

 

[icyroads]

Disagree that it means nothing and is all mental! This a time honored practice among conservative engineers called "de-rating". A fine practice and one I believe in myself. Electronics that run cooler last longer.

Yes, derating is a practice.
However, what is “enough” when it comes to derating? Certainly there’s already a “derating” margin engineered into the device, plus the outsourced internal components they use.
So, we end up with derating upon derating upon derating. How much is enough?
If they say it can safely support 30A at a continuous duty cycle, presumably with some derating built in, then why add even more derating?

 

[Hedges]

As an IC designer at HP, our documents said something like semiconductor lifespan is cut in half for every 10 degrees C higher junction temperature.

Designs are a trade-off, and an SCC could be designed considering PV array reaches max for a short time, some impact on lifespan. If over-paneling makes it run 100% for 5 hours per day, there could be a hit to life. Ambient temperature matters too.

Heating of transistors and inductors goes as the square of current, so operating at 90% of rated current would be 80% of rated temperature rise. Might be designed around 70 degree rise, possibly 100 degree. Having 80 degree rise not 100 could mean 4x the lifespan.

User decisions are also a tradeoff. Now you get to make yours.

 

[boondox]

Yes, derating is a practice.
However, what is “enough” when it comes to derating? Certainly there’s already a “derating” margin engineered into the device, plus the outsourced internal components they use.
So, we end up with derating upon derating upon derating. How much is enough?
If they say it can safely support 30A at a continuous duty cycle, presumably with some derating built in, then why add even more derating?

When I purchase a device I decide how much to de-rate depending on a number of factors. The history (or lack of) of the manufacturer, how mission critical the device is, cost, is there redundancy in the system, does the device get hot if I pull the max from it and so on. Some manufacturers with a good reputation you can trust to have de-rated already. Others you can't. Some applications are trivial and if the device dies, no big deal. Others are a serious problem if a device fails. Like pretty much everything there is no one size fits all rule. Intelligence guided by experience is all you really have (a quote from Nero Wolfe).

 

[rubberlegs]

Most MPPT solar controllers are at least 95% efficient. The amount of heat put off is therefore minimal.

I've read that this unit (DCC50S) gets pretty hot.

 

[boondox]

I've read that this unit (DCC50S) gets pretty hot.

Mine doesn't. After pulling the max for a couple of hours it is warm but not hot.

 

[curiouscarbon]

Yes, derating is a practice.
However, what is “enough” when it comes to derating? Certainly there’s already a “derating” margin engineered into the device, plus the outsourced internal components they use.
So, we end up with derating upon derating upon derating. How much is enough?
If they say it can safely support 30A at a continuous duty cycle, presumably with some derating built in, then why add even more derating?

if the reputation of a device warrants a personal decision to derate by more than 50% (half), then i suggest finding another device.

some manufacturers publish ampere ratings prominently that do not represent continuous usage.

continuous duty cycle ampere rating is what I want to see from a manufacturer, every time.

any published rating that assumes a duty cycle of less than 100% is... inconvenient.

 

[curiouscarbon]

Mine doesn't. After pulling the max for a couple of hours it is warm but not hot.

sorry to bother with clarification question.

can you touch it firmly for more than a few seconds without feeling pain?

kind of odd question, perhaps. if the heatsink is painful to touch for more than a few seconds, i usually consider it to be "hot"

if it is tolerable to touch continuously, then i would call it "warm"

again, sorry if this is overly pedantic ?

if a surface of any device is "hot" to me, i generally wish to cool it with moving air.

that said... some components can tolerate higher temperatures all day than myself.

however, most components survive a lot longer when the temperature is lower.

kind regards

 

[Hedges]

any published rating that assumes a duty cycle of less than 100% is... inconvenient.

But an MPPT is expected to see about 6 hours effective sun per day. Peaking for a while, and being powered up for about 12 hours.

SMA warrants their GT PV inverters for 20 years, their battery inverters for 10 years. Or a certain number of kWh production, whichever comes first.

Operating temperature of transistors, diodes, and electrolytic capacitors are probably the drivers for MTBF. A more complex model could be built, but hours and kWh simplify it.

if a surface of any device is "hot" to me, i generally wish to cool it with moving air.

Just a little air cools thing a lot.
Dedicating a little PV to extra airflow could pay off in equipment life.



Things can be run at full rating. You just pay for it in more frequent replacement.

 

[curiouscarbon]

But an MPPT is expected to see about 6 hours effective sun per day. Peaking for a while, and being powered up for about 12 hours.

hehe, good point ?

most devices seem to reach "steady state" operating temperature within 1-2 hours in my experience.

perhaps a more precise specification would be 6 hours or more operating at rated current. ?

 

[rubberlegs]

Can I plug in my old AGM charger into the DCC30S or 50S (still waffling on that decision)? So I'd have three inputs:

1. Solar into the PV input.
2. Alternator into the alternator input.
3. Iota DLS-30/IQ4 120VAC - 12VDC charger also into the alternator input. It puts out Bulk 14.8V, Absorption 14.2V, Float 13.6V. Or I could try tweaking the voltage as described in another thread on this site (here).

 

[boondox]

sorry to bother with clarification question.

can you touch it firmly for more than a few seconds without feeling pain?

kind of odd question, perhaps. if the heatsink is painful to touch for more than a few seconds, i usually consider it to be "hot"

if it is tolerable to touch continuously, then i would call it "warm"

again, sorry if this is overly pedantic ?

if a surface of any device is "hot" to me, i generally wish to cool it with moving air.

that said... some components can tolerate higher temperatures all day than myself.

however, most components survive a lot longer when the temperature is lower.

kind regards

I can easily keep my hand on it for as long as I want without it being an endurance contest. That is after pulling 50 amps for a couple of hours.

 

[curiouscarbon]

I can easily keep my hand on it for as long as I want without it being an endurance contest. That is after pulling 50 amps for a couple of hours.

thank you kindly for this clarification

 

[rubberlegs]

I can easily keep my hand on it for as long as I want without it being an endurance contest. That is after pulling 50 amps for a couple of hours.

Curious if you are putting your hand on the cover (the "front"), or on the cooling fins (the "back").