Autopilot Battery

[timeandtide]

The PNOR for the MGR states that 200ah is the maximum allowable for the house battery system and that an electronic autopilot requires a stand alone battery.

Is there a size limit on the stand alone electronic autopilot battery?

[captdan]

I had the same question ..... also, it should be clarified whether the stand alone auto pilot battery is part of the 200 AH or is it in addition to the 200AH ?

On the topic of extra batteries, NOR 5.1.2 F) states "A completely independent set of emergency LED navigation lights with an independent power source must be on board." Same question as above ...... Is this power source part of the 200AH House batteries or is it in addition to the 200AH ?

[timeandtide]

Thanks Dan, I am of the impression that the auto pilot battery would be in addition to the House bank as the language states “maximum 200ah for house system” then goes on to mention the need for an additional battery for the autopilot which would be electrically isolated from servicing the house loads.

I am currently planning out my electrical system and I am designing a system that will keep the batteries isolated yet get them all charged simultaneously from one source.



My interpretation of the emergency nav lights with their own power supply would be individual battery powered units, perhaps rechargeable but think of them like flashlights with their own independent batteries, not accumulative to the house service.

[timeandtide]

I also have a question about battery capacity at different voltages. I plan to run my boat on 24 volts and the NOR states a maximum capacity of 200ah at 12v. Can I carry 200ah at 24v as well?

[Daniel]

Jun 1, 2023 2:34:08 GMT timeandtide said:

I also have a question about battery capacity at different voltages. I plan to run my boat on 24 volts and the NOR states a maximum capacity of 200ah at 12v. Can I carry 200ah at 24v as well?

The rules may limit you to a 12V nominal power system in a strict reading, or they may just be unnecessarily over-specified in a few places.

5.1.2.L: "Max 200Amp Hour at 12v, 20HR rating, for house battery" in a strict reading would be requiring that the battery be 12V nominal. In a more general , yet reasonable, interpretation it may be assumed that the rule is intended only to limit battery power storage capacity, not voltage, and that it is specified as 200Ah 12V to make battery selection easier for the majority of people running a 12V system, where 12V batteries are frequently specified by Ah rating.  A more direct way of specifying the power storage capacity would be to use Wh, that would keep battery power storage the same across any voltage, but would could require a bit of simple math for figuring out what batteries to get.
200Ah x 12V = 2400Wh.   
In that general interpretation, that the rule is specifying a power storage capacity not a nominal voltage requirement, you could calculate the Ah size of battery for your 24V system:
2400Wh / 24V = 100Ah.  Those would be the same size, mass and power storage capacity as 12V 200Ah.

Applying the stated Ah limit across any other nominal voltage would result in more power storage, and doesn't seem like a reasonable interpretation of the rule...
200Ah x 24V = 4800WH.... your batteries would be twice as big and store twice as much power.


5.1.2.E: "12 V 3000 ltr per hour electric pump" In a strict reading here, your bilge pump would be required to have a 12V operating voltage. It may be that is unintended, and "12V" here is simply a redundant and a bit sloppy way of saying "electric"....

5.1.2.L: "100 watt @ 15v" and "200 watts at 15V" solar panels. Again, a strict reading of the text here says you must use solar panels with a 15V power output. That may well not be the intent of the rule, as the power output is fully specified with Watts, and the Voltage is largely irrelevant. That is, the same size of panel will have the same power output (Watts) regardless of the Voltage. 15 V solar panels would be suited to a 12V nominal power system. If you wanted to run a 24V system, you would just get 24V nominal solar panels at the same wattage, and you would have no advantage over anyone else.

So, an official clarification, and perhaps a few careful edits in the rules to remove any unintended limitations, would be advisable before committing to a 24V system. It gets a bit tricky when each rule does not have a single specific intent. I.e. 5.1.2.L has about 15 individual rules in it. If the intent was to specify a 12V nominal power system, that is not clearly stated as a separate rule

[timeandtide]

Thanks for the insightful reply Dan! I am a marine electrician by trade so I fully understand the implications of what I am suggesting. I naturally assumed that to run at 24v I would likely br limited to 100ah I was more seeking some clarification on the rule. I just prefer running at 24v as I can halve my amp loads and run smaller (lighter) wires. If I am limited to 12v that’s fine too.

[Daniel]

Jun 23, 2023 2:43:43 GMT timeandtide said:

I am a marine electrician by trade 

Hey Josh, I've been following your build through your posts. Looking forward to see your electrical setup!
I'm not building yet, but been following 5.80 since the start. Hoping to enter a future MGR.

Would def. like to see a clarification on the rules too. I doubt if restricting to a 12V system was intended. keeping the Amperage lower makes a lot of sense. quite a few electrical systems, so a lot of wire length there.

I haven't seen anything that would limit size on the autopilot battery anywhere.
Also, the motor are just limited to proprietary batteries, which is not much of a limit as there are proprietary inboard batteries that are pretty huge (e.g. epropulsion e-series batteries)

Also would be curious to hear the rationale of allowing wind generation, but not hydrogeneration.