Windlass battery charging

I want to charge two 110ah agm windlass batterys from the port engine of a 46ft power boat, i would like to use a BEP Marine voltage sensitive relay to charge the port engine battery and the windlass bank.
The total cable length will be about 30m, the alternator is rated at 80amps.

Would 25mm square cable be ok and do i need to put a fuse/breaker at both ends?

 

Hard to say. What is the windlass motor load rating..amps ? 12 or 24v. The high load on the system will be the windlass to battery leg. To avoid big copper cables and long expensive copper cable runs, and 30 meters is a LONG EXPENSIVE cable run, many yachts locate their windalss energy supply, a dedicated Battery bank, very close to the windlass. Shorter run, smaller cable simple installation. . The charge load is always smaller , so smaller copper cables might be aplicable for the alternator to battery link. . How many amps does the windlass use ?

be aware that the fastest way to burn up an elecric motor is to starve it of power with high power loss transmission. .
One knife style breaker at the power source to protect the cabling and windlass, is all Ive ever used. plus the normal control circuit small amp breakers. Your wnidlass hand book normally specifies cable size to run length and the correct amp and style breaker.

 

The battery bank for the windlass is located within 3m of the windlass which is 1500w 12v. Its the charge cables which will be run back to the engine room which is about a 30m run in total.

 

If you are putting in a normal charge of no more thatn 20% 45A will be the maximum current. 25mm square cable is AWG4 which is way too much for charging alone. If you mean 2.5mm which is about AWG14 (just a bit larger) It is unsersized. If the relays are at the alternator, fuses at both ends would make sense. Otherwise, you have a very long energized wire with no protection.

 

30m is quite a distance for that kind of current. The thicker the cables the better and the less voltage drop you will have over the 60m cable (2 x 30m).

2,5mm will be way too thin, it would act like a resistor instead !

Thumb suck, for that kind of current over that distance the diameter of the wire should be 16mm or more.

The purpose of a breaker is to protect your wiring, so yes a breaker either side would be ideal.

 

...yep fuses both ends as they can be power sources and you always fuse at the power source...also you can instal a fuse, it would be to make sure that the cable is never overcurrented, such as an alternator failure...I would run the heavier wire (25mm2), as Fanise says, less voltage drop, and better current flow with reduced head.

 

I'm a bit allergic to fuses. There is always that shuffle in the dark after the spare fuses that was never replaced the last time they blew...

You do get resettable circuit breakers, I would use them instead.

 

...whatever...sounds good to me, have to agree.

 

It's a matter of you have to protect you from yourself... or it usually ends up one bolt in the fuse, at about 497.3246113Amp fuse rating and a bolt missing from the rigging somewhere.

Wiring is never too thick, but they can be too thin.

 

25 mm2 is AWG 3, resistance 0.2 ohm @ 1000 ft.
30 m. cable length is 180 ft wire length, so 0.036 ohms total resistance.
Voltage drop 1.8V @ 50 A, that's about the maximum charging current you will get from a 14V alternator.

I think that is quite acceptable for 220 Ah battery capacity.

From post #4 your 25 mm2 has turned into 2.5mm2, very confusing .....

I share Fanie's feelings about fuses, but in this case I would certainly install one at the alternator end. Or a 50 Amp circuit breaker if you can get one.

 

Is it possible the windlass battery bank could recieve the full 80amp output from the 12volt alternator if so do the circuit breakers need to be sized for the full output?
(25mm cable and 30m total cable run)

 

Remember that normal house trip switches trips on overcurrent, there is a coil in series with the load that excites a mechnism that trips the power mechanically. If you take a mains trip switch and put dc through it it will also trip at a certain current. You will have to test with a current source, but in theory one can calculate the difference.

 

Im going to use the Blue Sea breakers they can be surface mounted. http://bluesea.com/category/3/10/productline/overview/13

 

Good choice. They are thermal, allowing 200% overload for 10 seconds before they trip, so 50 or 60 Amps nominal will not trip when everything is OK.

 

The size of the fuses or breakers should be somewhere between 1.25 x the expected current in amps and the ampacity of the wire. Some where in the middle is a good choice to avoid any nuisance trips.

Awg 3 is an odd size in North America but for awg 2 the ampacity is about 178 amps in engine spaces and 210 outside. For awg 4 the ampacity is 136 amps in engine spaces and 160 outside. I would allow for the full 80 amps which is likely on occasion as the batteries are AGM. AGM batteries can easily accept 1c if in bulk charge mode. I would use a fuse or breaker of about 100 to 125 amps. This is over any alternator output and under the wire's capability to carry amperage. You are fusing so the fuse (or breaker) protects the wire.