Relay ratings?

I'm sure this is probably a super basic question, but here goes:

I'm bringing back ~120A @~14v from alternator (via blue sea charging relay) to auxiliary battery in the rear. I'm building a compartment for my sealed AMG, but I still want to vent it to the van - 12v .1 amp fan, to run only when battery being charged. What relay would be recommended for such an application? I figured I'd find something here for the 120A rating, but I don't see anything that high. I've also read that really you're rating is in regards to the power, this being all DC, just VxA. Even so, I don't see the ratings in Watts, just amps, so not sure how to select proper relay.

Or... do I need something different than a relay??

thanks,
Erik

...some further searching turns up this, which seems to meet my criteria:

https://www.amazon.com/Support-Relay-Truck-Marine-Charge/dp/B00WMBUWKI?th=1

would be appreciative of those with more experience confirming that would work... cheers!

Erik

You only need to size the relay for it's load pull/draw plus the fan's load pull/draw.


Miniature automotive relay: ~10A @12V

https://ca.mouser.com/productdetail...bArVJter2K4oWA1tHY5ZZU%2bYhgWa/iGjv7Q39lOrw==

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thank you for the link - the current that charges the battery is still going through this relay though, correct? Unless I'm not understanding those wiring diagrams. The ~120A goes through the coil to close the contacts on the switching side correct? How would I land a 4AWG on that unit??

thanks
Erik

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veggiePNW said:

thank you for the link - the current that charges the battery is still going through this relay though, correct? Unless I'm not understanding those wiring diagrams. The ~120A goes through the coil to close the contacts on the switching side correct? How would I land a 4AWG on that unit??

thanks
Erik

Click to expand...

No, the current that charges the battery(house) doesn't go through the relay. You only connect the relay's control/trigger pole to the terminal under the driver's seat that is powered only when the engine is running, since the main wire from bank to bank is always live with one source or the other.



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hmmm ok, i'll have to check that out to see where to connect into that wire - didn't realize there was a better way to do that except to monitor the power line.... it's downstream of a charge control relay, so it's only sending power back to the rear battery when the engine is running.

veggiePNW said:

hmmm ok, i'll have to check that out to see where to connect into that wire - didn't realize there was a better way to do that except to monitor the power line.... it's downstream of a charge control relay, so it's only sending power back to the rear battery when the engine is running.

Click to expand...

Yes....but no, as it will still have current/be powered from the house bank.




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cool thank you for the tip. so it looks like I want to find D+, is that correct? document here looks pretty solid: https://sprinter-source.com/forum/attachment.php?attachmentid=30951&d=1299371780


thank you!
Erik

veggiePNW said:

cool thank you for the tip. so it looks like I want to find D+, is that correct? document here looks pretty solid: https://sprinter-source.com/forum/attachment.php?attachmentid=30951&d=1299371780


thank you!
Erik

Click to expand...

D+ is the ticket, at least for an NCV3 and as documented in the pdf, I'm not sure if that is entirely the same for your t1n... do a search here, or perhaps others can chime in.



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Quick look shows the T1N layout is similar there... don't have the time at moment to crack into that cabinet, but it seems access is good enough by just sliding driver seat forward all the way. Hope to wire up this week so I'll echo back, thanks much for the help!

<<< SCREEEEEETCH!! >>>

Duh, forget/scratch the relay, it's redundant.... just wire the fan to the D+.







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ha!! of course... .1Amps shouldn't be too much more to put onto that circuit

D+ located right where that PDF indicated. I couldn't quite open up the plastic box that held those three terminals, but I could unscrew (heads near ebrake) and then pulled box out with plenty of wire slack... think I'll remount in the rear for better future access. Fan for house battery coming next week... now... need to think of a good way to run the leads back to house battery behind rear wheel well after I've already tounge and grooved up the walls oiy.

veggiePNW said:

D+ located right where that PDF indicated. I couldn't quite open up the plastic box that held those three terminals, but I could unscrew (heads near ebrake) and then pulled box out with plenty of wire slack... think I'll remount in the rear for better future access. Fan for house battery coming next week... now... need to think of a good way to run the leads back to house battery behind rear wheel well after I've already tounge and grooved up the walls oiy.

Click to expand...

Through the floor in the seatbase are some openings, then along the chassis.
Don't forget to add a small fuse.

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