need advice best way to wire parallel switch(s)

[Charlyipad]

36' sailing cat- Current setup: port and starboard 9.8 tohatsu outboards. each isolated from the other. 12v starting batteries one in each hull. charged by alternators. House battery: light duty, VHF running lights, phone charger, depth sounder 12v charged by 100w solar panel, also isolated, located in console in center of boat (23' beam).

OK here is the goal: provide back-up power from either engine to the house battery and to each other. If I understand the CFR correctly, and that is why I am doing this, for coast guard certification, I need to have backup power sources for all "vital systems" . My concerns are weight, excessive wire runs, and messing up the alternators. Jumper cables not allowed.

Thanks for any tips!

 

[JamesG123]

They make battery charge controllers that prevent over/under discharge. Since you have solar as an input source too, some higher capacity charge controllers will let you input windmills or gensets, basically any input source as separate sources. In this case you only need three (solar, P & S engine batts.) So each of your engine batteries has its own controller that feed the house battery's charge controller when charging (running), but cut off when pulled down to far (not running) or when overcharged. The alts are protected from back voltage by diodes. Should be pretty much automated without needing any switches and crosswiring.

Its too late on a Monday nite to try any Askii art or look up links. Hopefully someone will either post details or correct my addled idea.

 

[Charlyipad]

They make battery charge controllers that prevent over/under discharge. Since you have solar as an input source too, some higher capacity charge controllers will let you input windmills or gensets, basically any input source as separate sources. In this case you only need three (solar, P & S engine batts.) So each of your engine batteries has its own controller that feed the house battery's charge controller when charging (running), but cut off when pulled down to far (not running) or when overcharged. The alts are protected from back voltage by diodes. Should be pretty much automated without needing any switches and crosswiring.

Its too late on a Monday nite to try any Askii art or look up links. Hopefully someone will either post details or correct my addled idea.

Hi James, I already have a 30 amp controller installed on the solar input to the house battery. I will look at it today, but i think it only has one input terminal.

 

[missinginaction]

Use a couple of Automatic Charging Relays. I'll post a link to Blue Sea Systems below. You're looking for a three battery two engine system. This would take care of the engines, there is certainly a way to insert another ACR into the system to address the solar panel you reference. I'll bet if you called Blue Sea that they would be happy to walk you through it.

Battery Management Wiring Schematics for Typical Applications - Blue Sea Systems https://www.bluesea.com/resources/170/Battery_Management_Wiring_Schematics_for_Typical_Applications

I hope that this article points you in the right direction.

MIA

 

[philSweet]

It isn't that simple, Charlie. If you post a diagram of your boat's entire electric system, that would help. We don't need the AC and DC distribution downstream of the breaker panels, but we do need the shore connection to AC panel, the boat's bonding system, generator wiring, all DC sources, and large integrated items such as chargers, inverters, and anything not routed through the normal AC and DC breaker panels (laundry, watermaker, air conditioners, etc.) And we need the outboard wiring for starting and alternator output.

 

[JamesG123]

Almost all of that is superfluous to the question he asked unless you are going to be the one doing the install. The outboards (and their batteries) are going to be self contained units. All the loads are going to be downstream of the breaker panels that is past the battery/charge controller(s) arrangement.

From his original post, I think he was invisioning a set of manual throw switches, which... will work. But require constant attention.

 

[Charlyipad]

Hi Phil, Thanks for the response. There is no AC , nor generator on the boat. There are three sources of DC power ; one battery for each engine, charged by alternators w/6A output, and one house battery inside the console, topped off by 100 watt solar panel, but Coasties say the solar panel is not considered a real power source. Anyway, Instruments and lighting are bare bones... running lights, anchor light, compass, depth sounder (garmin), VHF, spotlight, phone charger, spreader lights, no lights below deck. That's it. I still haven't verified what USCG means by "vital systems" but I am pretty sure I have enough amperage. to keep these things going for three hours.

It seems to me, I can accomplish this by running a large wire from the positive terminal n the port start batt to the positive terminal on the stb start batt, and a wire from the house batt to a connector in the middle, making a three/way junction. Do the negative side the same way. This would put all three batts in parallel. Then instal a big on/off switch on the positive wire close to the house batt, and a big on/off switch on the positive wire between the two start batts. When off these switches would keep all batts in isolation, just like they are now,. Seems I should be able to parallel the batts in any combination if wanted to, if needed. Tohatsu alternators are 6 amp output each at WOT. Tohatsu man says this is no porblem and switching in or out of parallel won't harm them. Any comments? Thanks!

 

[Charlyipad]

Ok another quirk. Tohatsu man also says grounds are probably "common" (not sure what this means) and that I don't even need to run a negative wire connecting all three batts. ? Comments appreciated!

 

[JamesG123]

It means that the alt is grounded thru the body of the motor to the water. Its battery still needs a +, - . The house battery will not have an "Earth", so no. you need the negative cables.
You should definitely have an electrician (preferably marine) who knows batteries look at what you are contemplating. And by look at, I mean you pay him more than you pay us to do it. Having batteries in parallel with differing levels and inputs is a sure way to damage them from over and under charge. Electronic charge controllers are cheap and easy to use these days.

 

[Charlyipad]

Thank you all for the responses. I am learning!
OK another question RULE 2000 UL rated pumps list a power consumption of 8.4a@12v 12a @ 13.6v.
For purposes of a load analysis which number should be used? an average?

 

[Charlyipad]

How do you properly size a fuse? My house total requirement is about 14.5 amps. That is with the VHF transmitting constantly. Batery cap is 75 ah. How much bigger than the total requirement should the fuse be? Thanks!

 

[Charlyipad]

Blue sea makes some heavy duty on off switches, that are UL rated, vapor proof, heavy duty and protect alternator circuits. I plan to use them for paralleling the batteries. One at each battery , so I can have any combo of three batteries I might want. How should I size the cables? Add up all the amperage requirements for each battery, but what about cranking the tohatsus? I am told they need about 30 amps to crank, so should I just add 30 to the total amp hours of everything else on the boat and size by the chart? Blue sea has a wizard. i just don't know what inputs to use, since we are talking about two different kinds of consumption cranking amps and amp hours?

 

[BertKu]

OK here is the goal: provide back-up power from either engine to the house battery and to each other. If I understand the CFR correctly, and that is why I am doing this, for coast guard certification, I need to have backup power sources for all "vital systems" . My concerns are weight, excessive wire runs, and messing up the alternators. Jumper cables not allowed.

Thanks for any tips!

If I understood your problem correctly, I would consider 2 X 70 Ampere Schottky diodes with, (should it be necessary}, to isolate the earth/common rail with 2 double throw switches. However you need to mount the diodes on a heat-sink and isolate the heat-sinks with a heat transfer/electrical isolated piece of material. Cost : diodes 2 x MBR7030WT 3 or 4 dollars, cost for isolator. a few dollar cents. Bert

 

[JamesG123]

Why connecting your starter and house batteries together with "dumb" switches is a bad idea:

 

[missinginaction]

Yessiree Bob, or James 123! That's why people invented automatic charging relays or ACR's. Take a look at the photo below. If you look closely you will see a little LED just to the right of the tachometer. That little light glows green when the batteries are connected (charging) and is off when there is no charge present. If I'm sitting at anchor, or at anytime when engines or the generator are not running I'd better not see a green light. If I'm underway or on the generator I'd better SEE that green light. Once installed it's simple, automatic and I don't need to do anything but notice the green light.....or not as the case might be. Simple!