DC - DC Charger Project

[TedS]

Another consideration in using the truck frame for the return path. If the truck battery negative is connected to the engine block and not the frame, the bond from engine to frame is a flat braided strap. It does not have the current capacity of the 4ga or larger wire.

[Guest]

Another consideration in using the truck frame for the return path. If the truck battery negative is connected to the engine block and not the frame, the bond from engine to frame is a flat braided strap. It does not have the current capacity of the 4ga or larger wire.

Ted, I stated the same in post #88 where we are in agreement. If folks want the possibility of a serious thermal event, I suppose another thread can be started in how to do that since one chassis ground method will certainly not fit all TVs'. A dedicated feed and ground return will guarantee success on every vehicle out there.

Jim

[Yoda]

New question
Fuses or circuit breakers or combination

My Renogy 60 amp charger showed up today and got to reading the manual (imagine that) they recommended fusing BOTH the input at 90A or close and the output side at 75A or close.

Jim Hogdrv made me aware of this type of fuse. https://www.amazon.com/dp/B07LC5CHW9/ref=emc_b_5_t?th=1 90A with holder is $37 or I can go with a 100A blue sea circuit breaker for about $42. https://www.amazon.com/dp/product/B0051P01BW Breaker is re settable, but takes up space. Rob Cate&Rob has alread warned me about lack of space in the engine bay. Its going to be a tough fit for the solenoid https://www.amazon.com/Cole-Hersee-2...NsaWNrPXRydWU= I did find a potted one 24213-1 but it $100 - still debating if it is worth the extra cost.

Fuse is simple ,right at battery post? (see post #70), but is a fuse and if it blows it is about $16 to replace https://www.amazon.com/Blue-Sea-Syst...36&sr=8-5&th=1 But its simple and takes up really no room (need to check hood clearance though) Circuit breaker cold be mounted somewhere I would guess, but wold need to be so I can see the status.

On the output side in the front bay I have room for the circuit breaker. The MRBF fuse holder wont fit the M6 studs on the Renogy (Dimensions here - https://www.amazon.com/Blue-Sea-Syst...36&sr=8-8&th=1)

So for now I am thinking MRBF at the battery and std Blue Sea 80 amp 285 series circuit breaker in the front bay of the 5th wheel on the Renogy output befor the bower bar connection..

Thoughts?

Thanks again
Keith

[Hogdrv]

Yoda
Keith

I can tell you that hood clearance is not a factor with that fuse and the reason I went with that instead of a cb was that I read the cb’s couldn’t handle the heat under hood. Here are some pictures of the engine bay and you can see the hood has an indentation above the battery. I did put a cb on the pin box before going under the fiberglass, I have no idea if needed or not but makes me fill good!

Jim

[Yoda]

Yoda
Keith

I can tell you that hood clearance is not a factor with that fuse and the reason I went with that instead of a cb was that I read the cb’s couldn’t handle the heat under hood. Here are some pictures of the engine bay and you can see the hood has an indentation above the battery. I did put a cb on the pin box before going under the fiberglass, I have no idea if needed or not but makes me fill good!

Jim

Interesting - I had not heard of the heat issue, but good to know. Answers my question.
Thanks
Keith

On edit Blue sea 285 series are only rated to 85C - 185F so I could see some possible issues. Depending on the mounting location me thinks it could be that hot or hotter.
https://www.bluesea.com/products/718...ace_Mount_100A

[TravelHabit]

TravelHabit ...
For the alternator, I inquired with Denso directly as a systems engineer in the auto industry and while I cannot share detailed information, I can share their concern with high draw at idle with a lithium battery connected to a TV depending in how the system is calibrated. From my own past experiences as a calibrator, smart alternators today are NOT calibrated by folks working with a trailer connected with a lithium battery bank, so I would not assume that because your alternator may be running cooler on the surface, it has relevance to all the other systems out there. Also the diodes in the rectifier bridge of your alternator would be a better focus rather than the surface temperature of the alternator housing...

Jim

Guest Thanks for looking into the alternator question. Funny, I let Denso know that I was a system engineer and they wouldn't budge on much information. The first person I talked to did note that Chrysler's standard capability is measured at 2000RPM whereas Denso uses another value. I was finally passed off to a manager (David S.) who explained that the alternator is an OEM captive and that Denso Japan does not allow them to have access to (or request) the spec sheet data. Sounded like they could be under an NDA with Chrysler.

I fully understand that the measuring the surface temperature of the stator is not precise and the internal temperature is going to be greater. I also realize that the diodes are likely the weak point as the temperature increases. However given the windings are copper which are an excellent thermal conductor they do provides good indication of what is happening temperature wise. In particular, I used the values to determine when the alternator temperature was close to a steady state value.

The key question I'd like to get your input on is the following: What is the maximum temperature a typical alternator can withstand in steady state operation? I've seen numbers like 320 deg (F) but again I've found no official documentation on that. I also asked Chrysler directly if there was a usage scenario that would void the warranty (we bought the Jeep in January). They couldn't tell me anything (suggesting I go to the Mopar website). Any clarification on steady state temperature limits would be greatly appreciated. With that I'd feel comfortable translating to a lower stator surface temperature value.

Finally I do expect that the the industry is not calibrating to lithium batteries. As you know, the key advantage of using the Renogy is that it isolates the TV battery and limits the current draw. So from my perspective it really doesn't matter what the load(s) are. It could be a combination of loads throughout the vehicle -- which includes its own inverter for the back passengers who could be running computers, DVD players and other items. What really matters is the allowed alternator temperature limit (even if just a rough value) or the maximum steady state current draw at the worst case idle RPM. Either one of those ought to allow us to bound a worst case usage scenario within some margin of error.

Full disclosure, I recently retired with 37+ years as a systems engineer and I have a M.S. and Ph.D. in engineering from UCLA. However this all doesn't matter one bit... there are plenty of technicians that know a lot more than I in their own area of expertise. No one can do much though if one can't even get basic spec sheet data from the designers! Frustrating since there most certainly is a requirement Chrysler put on Denso for design and acceptance testing!!

Earl

[Guest]

Guest Thanks for looking into the alternator question. Funny, I let Denso know that I was a system engineer and they wouldn't budge on much information. The first person I talked to did note that Chrysler's standard capability is measured at 2000RPM whereas Denso uses another value. I was finally passed off to a manager (David S.) who explained that the alternator is an OEM captive and that Denso Japan does not allow them to have access to (or request) the spec sheet data. Sounded like they could be under an NDA with Chrysler.

I fully understand that the measuring the surface temperature of the stator is not precise and the internal temperature is going to be greater. I also realize that the diodes are likely the weak point as the temperature increases. However given the windings are copper which are an excellent thermal conductor they do provides good indication of what is happening temperature wise. In particular, I used the values to determine when the alternator temperature was close to a steady state value.

The key question I'd like to get your input on is the following: What is the maximum temperature a typical alternator can withstand in steady state operation? I've seen numbers like 320 deg (F) but again I've found no official documentation on that. I also asked Chrysler directly if there was a usage scenario that would void the warranty (we bought the Jeep in January). They couldn't tell me anything (suggesting I go to the Mopar website). Any clarification on steady state temperature limits would be greatly appreciated. With that I'd feel comfortable translating to a lower stator surface temperature value.

Finally I do expect that the the industry is not calibrating to lithium batteries. As you know, the key advantage of using the Renogy is that it isolates the TV battery and limits the current draw. So from my perspective it really doesn't matter what the load(s) are. It could be a combination of loads throughout the vehicle -- which includes its own inverter for the back passengers who could be running computers, DVD players and other items. What really matters is the allowed alternator temperature limit (even if just a rough value) or the maximum steady state current draw at the worst case idle RPM. Either one of those ought to allow us to bound a worst case usage scenario within some margin of error.

Full disclosure, I recently retired with 37+ years as a systems engineer and I have a M.S. and Ph.D. in engineering from UCLA. However this all doesn't matter one bit... there are plenty of technicians that know a lot more than I in their own area of expertise. No one can do much though if one can't even get basic spec sheet data from the designers! Frustrating since there most certainly is a requirement Chrysler put on Denso for design and acceptance testing!!

Earl

Earl,

I can tell your plenty capable where to answer your question on temperature, I have no idea what the critical temperature would be. The feedback I received was based on a concern over diode temperature only. The reason I mentioned the calibrator perspective is that the lithium packs are not part of vehicle calibration so depending in how the system is calibrated could also determine if there is a risk. The Renogy will limit its current draw based on the output of the unit and the internal resistance of the battery so a large unit like a 60amp unit will pull close to 90amps at idle if the alternator is calibrated to deliver indefinite full output at idle considering other electrical loads like post start, heated seats and so on. Most systems these days are modeled where I doubt there is a temperature sensor on board since those add cost. If systems engineering was followed at Stellantis (Chrysler), there would be requirements set on the alternator with some restraints from from the supplier. Buy the way, I began my engineering career long ago at Chrysler and was in charge of a dyno cell (base calibration and combustion) at the Auburn Hills tech center. A palace in all respects. Send me a PM where I'm interested in what your working on.

Jim

[TravelHabit]

Will do on the PM. As far as temperature I don't know where to go next. It's very frustrating since I know (and the manager at Denso confirmed) the data exists!! Extensive searching on the internet for many many hours has not turned up real hard data. In the end this is why I ran my own temperature testing. I the end it seems Renogy should do better to help clarify this for their customers. Fundamentally, if cost is not the issue, what is the appropriate criteria between choosing the 20A vs 40A vs the 60A model? As I noted previously, the "rated" car alternator output is not the right measure since, in my case, I don't know the RPMs that represents.

Note that I was told by Renogy that the DC-DC converter will pull up to 95A!!! Of course that is all dependent on the voltage drop between the source current (typically the battery) and the Renogy unit... The greater the voltage drop the greater the unit will draw upon the battery/alternator to get the rated 60A output (I believe it's a buck-boost design)... It all talks to the efficiency of the DC-DC converter in supplying the rated charge current... This is one reason why I limited my voltage drop to less than 3%... As I recall, my draw was measured at less than 72A.

Don't know about other vehicles but I concluded there is a temperature sensor on The 2021 Jeep. I noticed in my test that at one point, as the temperature climbed, an auxiliary fan went on which provided extra ventilation around the alternator. That is, there was a new rush of air around the alternator side of the engine and not on the other side. THAT gave me a sense that the designers were aware of high current draw at low RPMs. I don't know that for sure though.

I'll try to post what I did and the results all on a separate thread but I'm having major computer problems right now (as well as another trailer modification in work ). I'm working on a bootstrapped system just to get me by... not fun.

BTW, just to be clear, I don't profess to be an expert on all this. My experience is not in the auto industry. I've just learned an awful lot in my extensive research (I can't help myself) and the journey to get the end state I'm trying to achieve in a safe and effective manner.

Earl

[Scott'n'Wendy]

New question
Fuses or circuit breakers or combination

You asked for an opinion, here's mine,
Fuses are more reliable and dependable. But...not as convenient as cb's. A cb being a mechanical device, can fail.
So, I would use fuses...and carry spares.

you know what they say about opinions. lol

[Yoda]

Update
I sent a question into Renogy on what size breaker to use on the output side. Manual says 75A or close. They recommended going withe 80A. I got the response within probably an hour of submitting the question, and that was after closing hours for them 3PM Pacific time. Not bad customer service - and on a Friday night too. .So now I can get the last of the parts ordered. 2 AWG wire showed up yesterday and today I ordered the solenoid and 2 AWG terminals. So when the new truck comes I will have almost all of the parts needed.

Keith

[Scott'n'Wendy]

Max temp rating on the welding cable from the sire you referenced is 105 C. That's mighty hot.

The 105*C is referring to the temp rating of the insulation, how much ambient heat it can take before melting, not how hot the wire will get when passing max rated current.

[Scott'n'Wendy]

Update
I sent a question into Renogy on what size breaker to use on the output side. Manual says 75A or close. They recommended going withe 80A.
Keith

If possible, verify you can stuff #2awg into the 80A breaker terminals. Sometimes terminals are just big enough for their intended purpose. (#4)

[Yoda]

If possible, verify you can stuff #2awg into the 80A breaker terminals. Sometimes terminals are just big enough for their intended purpose. (#4)

Everything uses ring terminals, including the breaker so I should be good, but I know first hand what your talking about. One trick mentioned here is to use crimp on ferrets on stuff in connections. It compresses the wire into a very tight neat bundle.

Thanks for the heads up.

Merry Christmas.

[TedS]

The 105*C is referring to the temp rating of the insulation, how much ambient heat it can take before melting, not how hot the wire will get when passing max rated current.

Keith was wondering about using ampacity to size wire.

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Current is measured in amperes or “amps.” You must use the correct size wire for the current (load) requirement of the circuit to prevent the wire from overheating.

[Scott'n'Wendy]

Keith was wondering about using ampacity to size wire.

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Current is measured in amperes or “amps.” You must use the correct size wire for the current (load) requirement of the circuit to prevent the wire from overheating.

I understand, but the 105*C you mentioned is the insulation rating, not the wire.