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Old 15-08-2016, 00:35   #1
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Boat: Oyster 435
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Power Management

Dear forum members,

I am trying to understand the electrical system of my sailing yacht as I would like to install a power management system and some alternative sources of energy (solar, hydrogen) at a later stage.

So far I have put together a drawing of what I think represents the actual situation of the electrical system by following cables around the boat (see drawing attached). I hope this makes any sense, as I am not an electrician, I am not sure about the graphical representation of the wiring.

In a nutshell, I can charge my batteries either from shore power, a generator, or the alternator of my engine. All inputs feed to a split diode charger which is routed to the batteries. My charger has a third output which I could potentially use to charge the genset battery. At the moment the genset battery is only charged by the genset (I assume). There also is a bow thruster connected to the service batteries. I also have an inverter which I havenít shown on the drawing.

My questions:
  1. I am looking at two different power management devices: the Sterling Battery Management Controller PMP1 or the Victron Energy BMV-702. I understand the Sterling Controller needs to be in the + System whereas the Victron is in the Ė System and requires less setup. I would appreciate if you could share your thoughts on these devices or indicate any other units that you would recommend.
  2. Is it a good idea to connect the genset battery via the CB to the third split diode and further to the charger?
  3. I was looking at the watt&sea hydrogenerator which I would like to install at a later stage and contacted them for advice but they havenít replied at all. They have a converter-regulator which combines their hydrogen input and a solar input (20A max). Do you think it is a good idea to combine these inputs in one regulator, or would you keep the solar input separate on another regulator?
  4. Where does the output of the regulator(s) best connect to, having in mind I would like to install the power management devices?
  5. I created an electrical budget based on the consumers that I have on board (file attached). The currents are taken from the manuals. I would appreciate if you could review my assumptions and provide me your feedback. From what I understand of my budget I wonít have enough solar power at anchor with one 128W panel but unfortunately I donít have any more space on my dodger other than 110x140cm.
Many thanks to all of you for your support in advance!

Best regards,
Attached Files
File Type: pdf Elecbugt_Belle.pdf (293.4 KB, 23 views)
File Type: pdf Wiring_Belle.pdf (131.9 KB, 16 views)

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Old 15-08-2016, 01:19   #2
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Re: Power Management

first understand the split diode. it is only splitting the alternator. the charger is just using it as a junction point. the charger is using 2 outputs going to 2 batteries the diode is irelivent, it's just a bolt in the middle of the charger wire.

if it has a 3rd I would run it to the gen battery for maintenance. but if you run the gen often it is not needed. if the boat sits unused all winter with shore power it's a good idea. run direct from charger to battery. not diode block

the victron 700/702 is good. it only monitors one battery. the house, you would have to rewire your main battery negatives to make it fit, with a common neg bus bar. instead of daisy chaining everything.

solar would go to battery pos and new neg bus bar. shunt goes between house bank and neg bus bar.

50a alt is pretty small. and diode blocks are old school. a big alt run direct to house bank, with a ACR / echo charger would hugely increase your charging.

get LED cabin lights! you have over 20a of lights listed.

hope you have some more fuses in the diagram not listed.

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Old 15-08-2016, 01:31   #3
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Re: Power Management

your budget looks really high. 500ah / day running 250 / day anchor?

you'd need 700watts of solar at anchor or 1400w while running to keep up (on a sunny day). and your battery bank should be about 3000 ah then which would be rediculas. (big enough for 3 days to 50%)

the AP is definitely way off. it only uses power while actually steering. so there is a duty cycle %
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Old 15-08-2016, 01:59   #4
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Location: Malaysia, Thailand
Boat: Beneteau Oceanis 430
Posts: 617
Re: Power Management

Yes consumption looks overstated. While its good to be conservative and overestimate consumption ( and underestimate charging) I reckon this one was a bit too conservative on the consumption?

If you like to run your generator then okay..

Personally I would add lots of solar and increase the house size. Remember, your 170 ah batteries are only 170 ah when brand new, usually even less. After some time they may be 150ah. And you should never draw them to 50% or less state of charge.

Change to led lighting, but good quality, not cheap ones, as they can give you trouble. Some cheap ones can't handle charging at marine battery charging voltage levels.

Here is a goldmine of excellent information:

Welcome To Photo Gallery by Compass Marine How To at

Ok I will say this also despite knowing some folks will scream herecy: I would consider tossing your thruster and windlass bats and draw from a 600ah -800ah house bank. But that's just me. Some people like it, some people scream. I suppose genny battery should be kept.. hehe. With auto low voltage start.


Ps. subject should attract the interest of some gurus soon (I'm not one)
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