โJun-09-2021 09:03 AM
โJun-22-2021 05:46 AM
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.
--------------------------------------------------------------------------------------------------------------------------------------------------------
This is intended as a general overview. I hope it will suffice.
โJun-21-2021 10:10 AM
โJun-21-2021 07:27 AM
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.
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.
โJun-20-2021 11:45 AM
โJun-20-2021 09:43 AM
โJun-20-2021 09:04 AM
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
โJun-20-2021 08:56 AM
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.
โJun-19-2021 03:57 PM
S Davis wrote:
So I just took some readings on my Redarc 50 amp the system has 25โ 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 6โ 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.
โJun-19-2021 01:44 PM
โJun-19-2021 12:23 PM
โJun-19-2021 08:45 AM
โJun-19-2021 07:44 AM
BFL13 wrote:
Imagining some numbers:
Output Watts = 40a x 14.6v (just before Bulk ends) = 584w
Efficiency 85% (WAG--same as a typical converter) so
Input Watts = X amps x 14v (alternator output) = 584 x 100/85 = 687w
So at 14v input (no voltage drop) amps = 687/14 = 49 amps
With 1v drop, at 13v input, amps = 687/13 = 53 amps
So with some better info you could get closer for the amps.
โJun-19-2021 07:23 AM
MEXICOWANDERER wrote:
The only reason I am engaging in this is for educational purposes ๐
MEXICOWANDERER wrote:
Unless an RV is "Hot Seat" operated, meaning driven day and night for weeks on end, any multi-stage voltage "steps" are ludicrous. The rig is simply not driven long enough in hours for voltage manipulation to matter. We're not talking about a manual wheeled battery charger here. Alternators are voltage regulated.
MEXICOWANDERER wrote:
It wouldn't see correction from 14.0 volts to say 14.4 voltage inside of eight hours of campsite continuous engine operation. Read this again. Still with me?
If a DC converter was designed for say 60 amp operation, then it presents a different issue. But it isn't and it doesn't.
โJun-13-2021 02:02 PM