House Batteries

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I will be replacing them soon, probably before the house bank dies because they are a pain. My older genius charger can handle anything but lithium.

This past week I installed two DC2DC chargers. One off the start for main engines, one off the start of the GEN. Port ALT goes to main start and SB to the GEN start. Both feed LFP house.
Then I realised my on board charger also charged those two batteries. Turned on the charger and current flowed to the house. :dance:
Now when underway the ALT's will charge house bank thru DC2DC chargers.
Whenever GEN is running that ALT will feed to House in addition to powering the charger. No need to replace the genius charger if it still works.
 
This past week I installed two DC2DC chargers. One off the start for main engines, one off the start of the GEN. Port ALT goes to main start and SB to the GEN start. Both feed LFP house.
Then I realised my on board charger also charged those two batteries. Turned on the charger and current flowed to the house. :dance:
Now when underway the ALT's will charge house bank thru DC2DC chargers.
Whenever GEN is running that ALT will feed to House in addition to powering the charger. No need to replace the genius charger if it still works.


Just be sure you don't overload the gen alternator. They are typically pretty light duty, expecting to only charge a start battery. Can you adjust/limit the DC/DC current?
 
Just be sure you don't overload the gen alternator. They are typically pretty light duty, expecting to only charge a start battery. Can you adjust/limit the DC/DC current?
Yes I could cut charge in half to 20A, good tip, I will have to check output and ensure it can handle 40A.
 
Yes I could cut charge in half to 20A, good tip, I will have to check output and ensure it can handle 40A.


Just as a reference point, a Northern Lights 12kw generator has a 40A alternator for the 12V version, and 25A for the 24V version. And with a small alternator like that, I wouldn't run it on a continuous basis at more than 75% of the rated output.
 
Just as a reference point, a Northern Lights 12kw generator has a 40A alternator for the 12V version, and 25A for the 24V version. And with a small alternator like that, I wouldn't run it on a continuous basis at more than 75% of the rated output.
I have heard 75% and also 80%. I have a 50A alternator so it should be OK at 80%.
What I cannot find is the reason why they cannot run at rated max output.
 
I have heard 75% and also 80%. I have a 50A alternator so it should be OK at 80%.
What I cannot find is the reason why they cannot run at rated max output.

They just aren’t built to run for long at rated output because they don’t have to do that. Start batteries don’t require much charging, and it would be overkill to use an alternator capable of running at full output for an extended period.

Use a temp gun on the alternator when you know its charging at max (or 75%) output and see if it overheats. I promise you it will cook itself if you run it continuously at 100% output. Derate it until you are happy with the temps.

Even large-frame, heavy duty alternators usually need to be regulated to less than max output if you want them to survive charging lithium batts.
 
They just aren’t built to run for long at rated output because they don’t have to do that. Start batteries don’t require much charging, and it would be overkill to use an alternator capable of running at full output for an extended period.

Use a temp gun on the alternator when you know its charging at max (or 75%) output and see if it overheats. I promise you it will cook itself if you run it continuously at 100% output. Derate it until you are happy with the temps.

Even large-frame, heavy duty alternators usually need to be regulated to less than max output if you want them to survive charging lithium batts.

I understand, do you understand why they are rated higher than what you should run them at. Marketing? why not say rated at 35A which is what you are doing derating.
 
I understand, do you understand why they are rated higher than what you should run them at. Marketing? why not say rated at 35A which is what you are doing derating.

You make a good point. I imagine their logic is that it will produce 50A for the period of time required (short) to serve the design goal of charging a start battery. Marketing dept takes if from there and says its a 50A and not a 35.

I run two large-frame heavy-duty 24v alternators and derate them to 82% of max to feed our LFP house bank without cooking. I smoked an expensive Balmar because I believed that it was built to take running at rated output. Sometimes I’m a slow learner but usually I catch on at some point.
 
I understand, do you understand why they are rated higher than what you should run them at. Marketing? why not say rated at 35A which is what you are doing derating.


I think most any mechanical device will last longer or shorter depending on how heavily you use it. We specified device will tell you what their continuous duty rating is, and also various forms of intermittent duty. We probably see this the most with marine engines where the same engine will have a continuous duty rating of X, and an intermediate duty rating of 2x. Marine gears are the same.


There are also lots of products where no distinction is made because in typical use it's not an issue. Take a shop vacuum. What the hell is "peak HP"? It's some maximum something that someone saw somewhere, sometime, and is the biggest number they could defensibly put on the product. So yes, marketing.


Engine alternators are designed for two things, recharge a start battery which takes very little, and carry ongoing loads for the vehicle like lights, heater fan, HVAC, etc. These loads are max when you first start the engine and battery recharging takes place, then drop down to the background loads. Given this usage pattern for 99% of engines, alternators are rated accordingly, and the nameplate rating is for intermittent, not continuous duty. The engine itself is the same. Your car's engine may be rated at 200hp, but they know it will never be run that was for more than brief moments, and I can assure you it won't last very long if you ran it flat out continuously. Construction and farm equipment is different and is expected to run continuously, so engines are rated accordingly. With boats, it depends on the boat's usage, so marine engines are rated accordingly.


Getting back to alternators, I don't think anyone ever asked about alternator ratings until the advent of large house battery banks, and even then lead batteries get to acceptance pretty quickly and reduce the alternator load. The bottom line is that with the possible exception of large alternators designed for busses and emergency vehicles, all alternators are rated for intermittent duty.


I have NEVER seen an alternator manufacturer specify a duty rating. Nor have I ever seen a spec for max allowed rectifier temp, or max allowed stator temp (the two hottest parts of the alternator). All they specify is max ambient temp, e.g. the temp under the hood of a car, but without any loading specs or assumptions. It's utterly inadequate for designing any sort of power system, but it's all we get. Thanks guys, we really appreciate the help... but empirically it's been shown by people messing with large house banks, especially LFP where full output will be demanded for 100% of the charge cycle, that the continuous duty rating of most alternators is 70-80% of the nameplate rating. Big alternators can typically do more, and small ones less. Mine put out about 85% when regulated to limit the rectifier temp to 100C.


So yes, marketing.
 
You don't have to look far to see similar ratings...
Is that gen capable of putting out max power in continuous duty?
How about your main diesel engine... HP output if run 24/7 in a commercial application?
I think you will find situations where there may be 3 or more ratings for the same engine... recreational use, intermittent commercial & continuous duty?

"All diesel marine engine manufacturers have a ‘duty-cycle’ rating classification system complete with their own terminology. However, all manufacturers use the same 3 determinants to classify each rating; load factor, typical operational hours per year and typical full power operation hours. These ratings should be applied on the basis of vessel operations, the type of boat/hull design, and the power demands of the marine engine. Since more than one rating could apply, we’ve provided a list of 5 duty rating descriptions to help you determine which category your marine operation falls under."

I'm sure engines in each of those categories will have different components that meet the various demands.
 

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