Couple of questions about DC-Dc charging

MEXICOWANDERER wrote:

ALTERNATOR CAPACITY
I know of no current OEM alternator that can endure maximum amperage output for other than a few minutes. The design limitation is primarily in the rectifier system principally heat sink radiating area in conjunction with airflow temperature and CFM. There is no magic design formula, and increasing the capacity of the rectifiers is not a magic solution. A heat sink is good for so many vf watts of saturation and no more. Extremes in temperature cooling air inlet aggravates the limitation.
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This is intended as a general overview. I hope it will suffice.

that was great and confirmed what I thought, Ill have to dig into the altanator types a little more as what I found they started using versions of mine in 20004 but that could be special cases.

for myself I do have a 200ish amp ecu controled altanator and I am looking at running it with the 40Amp DC to DC charger and I am also planing to run big enough cable to the charger to keep the voltage drop to less than 1%. I am hoping to keep my load from the DC to DC when it is at its max out put to a point where the altanatore never sees over 50% usage in a normal situation.

Steve

When I post a reply and specify a particular charging system and a particular battery, I mean that particular charging system and that particular battery chemistry. If you want an opinion on a different setup, then so state it. "How about an X system with an X battery?"

As far as the charging system is concerned, the Ford 3G, 4G, and 6G alternators are the only models with the OPs stated output amperage. The ECU models begin at 135 amperes and end at 270 amperes, some are dual alternator models.

Acceptable charging profiles are radically different for lithium chemistry batteries. So a charging system that is acceptable for use unchanged with an absorbed glass mat chemistry may be totally unacceptable for use with a lithium battery.

To compound the matter, newer vehicles control charging profiles via the central ECU and ignore earlier charging regimens in favor of protecting power generators or squeezing an extra tenth of a mile per gallon out of fuel. And again, newer systems do not incorporate charging algorithms for lithium chemistry.

Therefore, the use of a throttling resistance wire to protect an alternator from overheating is utterly inappropriate when lithium batteries are involved. The keywords are utterly and inappropriate.
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Moving on to other systems, I have noted that as far as lithium batteries for RVs is concerned, different manufacturers have listed different recharging profiles for their products. Usually, limitations on voltage are the key values to keep in mind.

Thus, I cannot help but feel that any and all models utilizing OEM specifications for charging system performance are totally inappropriate for use with lithium chemistry batteries. All, means, from the 1920s to 2022 inclusive.

Therefore, with lithium chemistry, a DC to DC power supply makes perfect sense as long as it's charging profile agrees with specifications put forth by the lithium battery manufacturer.

In the choice of a DC to DC power supplies, amperage limiting to protect the alternator(s) is automatic.

But total capacity of a DC to DC converter must be considered. For an example, a 20-ampere converter used on a vehicle with an existing 30-ampere hotel burden means the system would endure a net battery discharge of ten amperes while traveling down the highway.

ALTERNATOR CAPACITY
I know of no current OEM alternator that can endure maximum amperage output for other than a few minutes. The design limitation is primarily in the rectifier system principally heat sink radiating area in conjunction with airflow temperature and CFM. There is no magic design formula, and increasing the capacity of the rectifiers is not a magic solution. A heat sink is good for so many vf watts of saturation and no more. Extremes in temperature cooling air inlet aggravates the limitation.
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This is intended as a general overview. I hope it will suffice.

BFL13 wrote:
Steve, IMO that output wattage limit is "nominal" not for real, that goes with the "12v nominal". IE, 20 x 12 = 240 and says 250 limit, and 40 x 12 = 480 and says 500 limit.

I would agree with you but the spec sheet says "Max output = 500 watts" if they didnt have the "Max" in there I may think it is a nominal thing, so I think they looked at the combanation of different charge profiles and such and just rated it for the highest senerio which is fine by me.

BFL13 wrote:
I still think you could get the 40 and don't have to settle for the 20. I have a 105 amp alternator in the truck with the 20 so your 220 amper should do ok with a 40 in yours IMO.

ya I think that is what I have decided on, was just looking at different brands now, but the Renogy looks like the one I'll get. would be nice after a couple days of rain to just hit the remote start on the truck and in 2.5 hours have the batteries almost full again. would be like an auto start genny ;)

Steve

This is more confusing than an income tax form.

Steve, IMO that output wattage limit is "nominal" not for real, that goes with the "12v nominal". IE, 20 x 12 = 240 and says 250 limit, and 40 x 12 = 480 and says 500 limit.

To meet the actual specs of doing 40 amps at 14.7v output, that would be 588 watts right there. I have seen 20 amps at 14.7v holding on my 20 amper for 294 watts (where "nominal" is 250w)

I have to redo my test using a simple load instead of the inverter and fridge that confused things. I don't have a good way to measure input amps, but can improve the jury- rigged ammeter connections. I plan to also try it with my fat wire long jumper cable set, to simulate a fatter wire installation from engine batt to Renogy to get a better notion how much that would help.

Whatever, I still think you could get the 40 and don't have to settle for the 20. I have a 105 amp alternator in the truck with the 20 so your 220 amper should do ok with a 40 in yours IMO.

MEXICOWANDERER wrote:
Please describe to me how multi-stage charging benefits a battery bank on a very very long 10-hour vacation driving day?

Stick to the program: A high amperage integral voltage regulated alternator. An ECU charging unit is a totally different animal.

Specifically *current limiting* is the objective to safeguard the alternator.


Thank You

ok so you totaly ignored my question and just repeated what you already said. in this spicific case yes it was a agm which uses charge profiles very close to a starting batteryand I agree a full days drive wont hurt anything. in the case of LiFePo4 where it requires a higher charge profile and such (which is in the context most times I see DC to DC chargers brought up) how does this change.

and we are not sure what year the posteres truck is, maybe that should have been one of the first questions as ford started using ECU controled altanators in the early to mid 2000's so his truck could very well be one of them. maybe we sould ask now before we keep going with this line of recomendations. either way he won't harm anything going with the DC to DC charger.

BFL13 wrote:
Not quite how it works, at least AFAIK.

Your Renogy does 40 amps output no matter what the input voltage is within its rating for that. The output watts (if it is like other chargers, which I assume to be the case) uses the battery voltage of the battery being charged, which rises as it is being charged. So it goes from say 13.5 to 14.5 to use as an example.

Battery voltage rises to the rated Vabs and then holds for the Absorption stage while amps fall. So highest watts with highest voltage to go with the 40 amps just before they taper, is just before Bulk ends. Pretend that is 14.5v and you start with 13.5v once the battery sees the charger (up from say 12.3 or whatever it was)

OK, so your range of output watts is 40 x 13.5 = 540w to 40 x 14.5 = 580w

"Efficiency" is watts out vs watts in (higher than out) so if 87% is it (here is another wrinkle-- note that MPPT controllers have more efficiency doing same to same voltage than higher voltage to lower voltages. So the efficiency of the DC-DC could well be like that, and depends on how much different the input voltage is from the output (house) battery voltage.)

Anyway pick 87% for this example and input watts will range from
540 x 100/87 = 621w to 580 x 100/87 = 667w

Now we need the input voltage, which will be from the truck's battery as regulated by the alternator, with some voltage drop. (which depends on the amps--higher amps, more drop)

So pick 14v as a likely engine battery voltage, 667/14 = 47.6 amps with no voltage drop.

If you have 1v drop on the wiring R, then 667/13v = 51.3 amps

That is only 3.7 amps difference with a voltage drop of 1 volt. If you had other watts from calculations with better numbers, it would still show not that much difference in amps from using fatter wire.

It would take a really big voltage drop to get 60 amps instead of 43 amps as was measured in that earlier post comparing installations. IMO there must be more to that comparison than we have data for, but you can see it is not as calculated above using the numbers I picked.

Anyway, IMO you could get the 40 amper and it would draw under the 60 amps and only briefly at that near the end of the Bulk stage. If you found it was over-tasking the alternator, you could choose to drop the output to 20 amps using that Renogy feature. If you got the 20, you can't make it into a 40.

You could use fatter wire from the Renogy to the engine batt, but as seen above, it is worth maybe 4 amps per 1 volt drop, so no need to go crazy on how fat to go.

Somebody who is better at these calculations can "check my work", but I think it is in the ball park.

not sure who your answering as you didn't use a quote, so it makes it hard to tell who you are refuring to,but if it is me then...

it doesn't put out a solid 40amps no matter what the input voltage is. right in the specs it list its max output in watts, not amps. the only reason for the amp rating is for comparason and yes at a spicific input voltage it will put out this many amps, but if that charge voltage it sends to the battery changes the output amprage will vary as it is limited by the wattage output.

Because the output voltage changes with the chemistry and "stage" the charge is curently in, the amprage changes with the voltage change. for example if your hard limit is 500 watts for an output, you can get there at 13.6 V, 14.6V, or 12.5V for the first you will have 37.76amps and for the second you will have 34.2 amps for the last you will have 40 amps. so if there using 12.5 as a referance voltaage for the standard it is a 40 amp (max) charger, but once again advertising tricks us as they left the "Max" out of the discription, but they did list the maximum wattage in the specs.

to get that on the output you would have to add the efficency in to get the input wattage to get that output and then do the same thing with your incoming voltage to get the new wattage and that actualy is how it works. of course there is line loss and such which like I said can be reduced with larger wire and such and yes that does cost money, but it will make your alt last longer so its a trade off that only the individual person can make. for me I have to run new wires anyways as the factory wire is way to small and the difference between a 4ga wire cost and a 0ga would be less than 50 bucks in my case.

Steve

S Davis wrote:
So I just took some readings on my Redarc 50 amp the system has 25’ of 1/0 DLO from the engine compartment to the bed of the truck where the charger and batteries are located. Charger ties into a 600 amp buss bar with about 6’ of 3/0 DLO to two sets of Trojan T105 batteries.

Truck idling on cold start.


Batteries starting at 12.4 volts no load.

Truck charging voltage 13.85 volts at 37 amps to the Redarc.

Redarc voltage 14.25 and 18.4 amps charging.

So that is 13.85 x 37 = 512.45w in vs 14.25 x 18.4= 262 out, and 262/512 = 51% system efficiency. Can that be right?

That made me go out and try some measurements with my 20 amp Renogy set-up where the input is via OEM (mostly) 7-pin to the camper.

I used the inverter to get some load on the full batteries so the Trimetic could show whatever the Renogy did. (However the Renogy load started at 19.7 and fell to 17ish later. Values kept changing with the inverter involved. EDIT--forgot the fridge 120v element draws less when it gets hot?--not a good choice for this test! Hard to take a snapshot running back and forth, can't be two places at once! I jury rigged an analogue 60 amp ammeter to the 12v 7-pin wire close to the camper end.

Truck started in idle at 14.5 volts but warmed up to more like 14, so I will use voltages from when warm. Had only 18.x amps of load I could find without the MW (fridge on electric and some fans) so hoped to see some pos on the Tri to get near 20 for output amps. Battery voltage from Trimetric.

Voltage drop from engine batt to Renogy. Renogy off, saw 14.0 at engine batt and 13.75 back at jury ammeter no amps. With Renogy on, it was 13.8 and 10.0 volts, so quite a drop so will use 10v as input volts--yipes! The engine batt voltage measured lower too, notice.

Ammeter was at roughly 30 amps on that jury wiring and at 10v, so call it 300w input. ( not very exact!)

Output was about (kept changing, hard to capture) 12.5v and 17.3 amps or 216w. System efficiency was 216/300 = 72%

but most of that must be my 7-pin wiring and the jury- rigged ammeter's R. The conversion voltage was 10 boosted to 12.5 for whatever Renogy efficiency that is at.

Bottom line is that it did draw more like 30 amps and output was under 20 in that test.

So it seems reasonable that with high R wiring to engine batt you could well see 60 amps with the 40 amper drawing near 40.

( If I want my 20 amper doing all it could, I should indeed improve that input wiring set-up. )

Please describe to me how multi-stage charging benefits a battery bank on a very very long 10-hour vacation driving day?

Stick to the program: A high amperage integral voltage regulated alternator. An ECU charging unit is a totally different animal.

Specifically *current limiting* is the objective to safeguard the alternator.

1. PROTOCOL A) A specified length of cross-link insulated tin plated fusible link wire



PROTOCOL B) A specified current limiting D.C. to D.C. controller.

Some hints: The current limiting wire is copper. Terminations can be soldered. It's routing is from the alternator or high amperage junction to (preferably) an automatic charging solenoid like a Blue Seas or Sure Power bi-directional charging solenoid that allows reverse direction charging from house to chassis battery. Remember the circuit is 100% automatic.

Or route a huge lead cable to say an 80-ampere D.C. to D.C. converter.
Here you can list perceived advantages. Take in consideration fusing protection and reverse circuit chassis battery charging.

Option A) Uses $15 fusible link wire and an $80 smart solenoid

Option B) Uses a converter, an overload protector circuit and whichever way to reverse charge the chassis battery.

Thank You

So I just took some readings on my Redarc 50 amp the system has 25’ of 1/0 DLO from the engine compartment to the bed of the truck where the charger and batteries are located. Charger ties into a 600 amp buss bar with about 6’ of 3/0 DLO to two sets of Trojan T105 batteries.

Truck idling on cold start.


Batteries starting at 12.4 volts no load.

Truck charging voltage 13.85 volts at 37 amps to the Redarc.

Redarc voltage 14.25 and 18.4 amps charging.