croakz":9j8n4q4e said:
Submariner":9j8n4q4e said:
The factory uses a Kisae DMT1250 and it's located in the port lazarette, all the way aft, port side of the locker.
Hey Martin,
I saw the Yamaha 250 and 300 outboards can put out 70amps from their alternators. But that's at WOT? Any issues with a 50amp DC-to-DC pulling that from the alternator at say idle? Thanks.
- tom
Feel free to give me a call anytime to discuss your upgrade in more detail.
The Yamaha F250 and F300 are the same motor. The 70 amp alternator is a marine alternator, meaning, it's wired such to give out most of its amps at lower RPM's. It'll reliably output 20 amps at 1200 RPM (a little above idle), and should put out the max amps at 2,500 RPM and above.
Being a 70 amp alternator, you'll never see 70 amps from it. I've measured on my battery monitor as high as 50 amps.
At idle, (about 650 RPM), usually there's not enough amps to engage the DC to DC charger. I see that on my Orion-TR 30amp DC to DC Charger. I usually have to be in gear, or bump the throttles (with the boat still in neutral) up to around 900-1200 RPM's to see reliable charging which is usually around 20 amps.
Using the engine as a generator when at idle is a bad idea anyway. It's one of those things that I've changed my mind on. To get 20amp-hours back in the battery would require 60 minutes of 1200RPM idling of the engine. 20ah on a 320ah battery is a drop in the bucket. The wear and tear on the engine isn't worth that 20ah in my opinion. It'd be better to upgrade solar instead.
The unwritten rule for sizing DC to DC chargers with LFP setups is to size it at 1/2 the size of the alternator. So for a 70 amp alternator, a 35 amp DC to DC charger is a good choice. The reason behind this rule is most LFP battery banks are large. That's precisely why we switch to LFP, we want more power. So the alternator will work harder, at or near capacity, for much longer periods of time. This runs the risk of overheating and burning out the alternator. By sizing the DC to DC charger at 1/2 the size of the alternator mitigates this risk. The OrionTR 30 amp chargers are technically 35 amp chargers in cold weather (anything below 70 degrees, which is PacNW weather).
The Kisae DMT1250 is a 50 amp DC to DC charger. It's what the factory uses on their LE's. I've not heard of a single alternator overheating on any R27-OB LE. But also note, you would most likely need a DVSR in front of the DMT 1250 so that it knows when the engine is running and when the engine is not running. The factory installs a BEP DVSR to accomplish this function. The OrionTR-30's don't need a DVSR as they have a built-in feature to detect when the engine is running and when it's been turned off.
