is the redarc bcdc1240d too much for a 75a alternator?

[airbats801]

We are building a new setuo foir my friends pickup. Nothing fancy. it will mainly be powering a older engel 30l and a iceco 45l. Currently it has a siomple bluesomething lkoad detecting switch, which kills the battery after a week of being off. It seems to work fine for short trips on a single 30l engel. I think we will be going to 2 gc2 batteries now, polus some solar, maybe 2 or 3 panels on his rack. He picked up a bcdc1240d, but we are wondering if it's going to draw a tad too much for the 70 to 75a alternator he has on his old little pickup considering I know these are peak numbers and non sustained. I think the goal is 2 or 3 days without running.

 

[emulous74]

When I spoke with Redarc about combing multiple bcdc's (cab, canopy, trailer), they said they don't recommend going more than half of the alternator's output for the total bcdc draw. Mind you this was for a modern truck, that obviously has more load for all the factory electronics, etc. So while it's possible, you would have to watch closely to see if it's effecting the normal running of the truck. Personally, I think a 40 amp draw is overkill for what you are planning on powering, I would suggest selling the 1240 and getting a 1225 or 1220 and play it safe.

 

[pugslyyy]

How old is that alternator? Consider just dropping in a new one with higher rated output. It probably will be pretty inexpensive.

 

[Roaddude]

.
Perhaps @REDARC_Ryan will chime in here. He's joined a couple adventure forums lately. As a REDARC employee who advises on all sorts of scenarios, he's helped several people quite a bit.

He's posted his email on prev threads here on ExPo as rthurston@redarcelectronics.com .

Good luck getting it sorted out the way best for your situation.
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[airbats801]

it actually is a upgraded alternator lol. considering the 83 mighty max came with a 45a alternator originally. we put a starion alternator in, which was pretty good sized for the 80s. We may look at swapping to a larger frame alternator eventually or getting one custom done, but for now this is what it's getting.

 

[Bart_from_Antigravity]

You may want to consider upgrading to a lithium 100ah battery of some nature. It will charge faster, supply more power for the space it takes and weigh less.

I use a REDARC BCDC 1240 with my Antigravity V2 100ah Deep cycle lithium battery with my Iceco VL 45 Pro and charge up misc other devices. from 30% SOC to 100% it only took 2 hours to charge while driving in my 07 FJ Cruiser.

 

[mechengrsteve]

Alternator ratings are just a point on the power production curve and really only useful to compare alternators. It's not a maximum and definitely not a continuous duty. A 75A alternator WILL produce 75A at 6000 alternator RPM into a resistor load bank, (not a lead-acid battery). They CAN produce more at higher RPM or to a lower resistance load such as a lithium battery. Manufacturers do not rate this output as continuous nor do they specify any output as continuous. I can guarantee you, that any alternator, run at its rated output, will overheat and burn out, probably in less than 30 minutes. Assume an alternator will put out 1/2 of its rating continuously and you will be close. Also, assume the reason the alternator is on the vehicle is that the vehicle load alone is probably 30-40% of the rated or 60-80% of the CD capacity of the alternator (~30A) and that you really only have ~10 amps of additional capacity.

A B2B is rated on its OUTPUT and because it pushes out more voltage than it receives. The input amperage will be somewhat above the output. For example, for an output of 40A at 14.6V (584w), it will have an input 584w/~13.8V = 42.3A.

I hope the answer to your question is obvious but the numbers will tell you what size of alternator you need to increase to if you continue.

 

[DiploStrat]

Some simple, and probably safe rules of thumb:

-- Production alternators should not be loaded to more than 50% of their advertised capacity.

-- A B2B will only output its rated output, regardless of the demand.

-- Much of the time, a B2B is boosting the voltage, which it does by pulling in more amps. Thus its actual demand on the alternator can run 10% or so higher. REDARC, for example, fuse their 50A models at 60A.

So a B2B is a nice way to limit the demand on your alternator, just remember that that demand may be 10% or so higher than the rated output.

Also, time matters. Calculate how long the charger is going to be running at full output. For safety, I would calculate 100%. Thus with a 100Ah lithium iron battery and a 50A charge source, I would guesstimate two hours at full output. That can be a serious load on the alternator. (Would actually do that, but you don't want to overstress things.) (Sadly, this is a do-what-I-say example; I am much harder on my alternator in the summer with my cab air conditioner. )