External bridge rectifier for T1N

sipma02

Member
As I'm designing my solar + alternator aux battery charging system, I am wary of pulling too many amps from the alternator (I have a 150a) and starter battery. I'd like to charge my future 280ah Lifepo4 bank at around .5C, and to spare the technicalities, that would be around 140 amps. Obviously too much to draw from the stock 150a alternator for continuous duty. So I'm going to be limited to around 50 amps of charging current, mostly because I can't find a DC to DC battery charger that will charge higher than that. Realistically I'm figuring that 50a charger will pull around 60-65 amps from the starter battery/alternator. According to this thread (esp post #9), it seems okay to draw 90-100 amps, but that might be pushing it.

My main questions: Is pulling 60-70 amps from a 150 amp alternator (via connecting to the start battery, fused of course) okay to do for extended usage? If not, would something like this external bridge rectifier (https://alternatorparts.com/quicktifier-external-bridge-rectifier.html) help mitigate the potential heat development?

Edit: I guess this should probably be in the T1N section
 
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marklg

Well-known member
For the T1N, I am using a Sterling BB1260 which takes 60A from the alternator with no issues. The number of 40A is what is available after all the vehicle's systems use what they need. The Sterling is set to wait for two minutes after the engine is running. By then the glow plugs will have stopped pulling current, and they pull a lot.

I would think the limiting factor on the alternator would be the windings as much as the diodes. Adding more diodes would not help that and in my opinion, messing with an alternator like that makes it less reliable. If you want more current, which I do not believe you need, install a higher capacity alternator or a second alternator.

Regards,

Mark
 

autostaretx

Erratic Member
As marklg wrote, the limiting factor is the windings ... in fact, it's the ability to *cool* the windings.
That's one reason the high-rated alternators are physically bigger ... more metal and more airflow.
(don't try to draw lots of current for protracted periods at low engine RPM ... lack of cooling will hurt the alternator)

Consider your *other* loads on the alternator ... do you have a rooftop air conditioner?
MB's "40 amps to the house" allotment includes that load "on the side" as part of the alternator's non-house duties.
If you don't run the rooftop AC, you've got all of its fan-power (30 amps?) available for house-charging.
The basic T1N only had a 90 amp alternator (and still allowed 40 amps for the "house").

If i recall correctly, at worst, there is a 200 amp alternator available that fits the same space.

--dick (not demanding much from his 115 amp alternator. Someday it'll get a relay to the house bank)
 

sipma02

Member
For the T1N, I am using a Sterling BB1260 which takes 60A from the alternator with no issues. The number of 40A is what is available after all the vehicle's systems use what they need. The Sterling is set to wait for two minutes after the engine is running. By then the glow plugs will have stopped pulling current, and they pull a lot.
Good to keep in mind. I've got my eye on the Kisae DMT1250, which does not have any sort of time delay built in. I think it would be easy to use the D+ wire to control a time delay relay set around 2-5 mins to achieve this.

As marklg wrote, the limiting factor is the windings ... in fact, it's the ability to *cool* the windings.
That's one reason the high-rated alternators are physically bigger ... more metal and more airflow.
(don't try to draw lots of current for protracted periods at low engine RPM ... lack of cooling will hurt the alternator)

Consider your *other* loads on the alternator ... do you have a rooftop air conditioner?
Nope, no rooftop/rear aircon, so I should be good there. But I can easily imagine getting stuck in traffic, at or around idle for a period of time, so I want to design my system with plenty of safe margin. If my current alternator goes bad, I will probably replace with a 200 amp Bosch unit. But I want to keep it in as good of shape for as long as possible!
 

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