Need help with calculations

[ChrisOlson]

You can get them either way. We got a mechanical contactor type in our boat. But they make semi-conductor ones too that use diodes. The mechanical contactor ones are more efficient and waste less power.

[J4mie82]

It is a hybrid battery made by alphaline but I read some good reviews.

I had looked into ACR's but with the engine battery being old it will just drain my lesuire battery.
The engine battery still does the job of starting the engine so I'm thinking uf it works don't change it.
I bought the boat for £1000 so don't want to kit it out too much just have a nice easy way of charging the 2 battery's easily. They are sat next to each other and are bith installed with quick release terminals so might try what the sunking said about seing if this 88ah 'leisure' battery has enough cranking power and starts the engine

Thanks for the help

[Sunking]

You can get them either way. We got a mechanical contactor type in our boat. But they make semi-conductor ones too that use diodes. The mechanical contactor ones are more efficient and waste less power.

OK the reason I ask and you probable see it coming; It is real dang dangerous connecting batteries together when they are at different SOC voltage. Anything more than 1/10 a volt can weld contacts and melt wiring. I assume the mechanical units Break before Make?

[ChrisOlson]

OK the reason I ask and you probable see it coming; It is real dang dangerous connecting batteries together when they are at different SOC voltage. Anything more than 1/10 a volt can weld contacts and melt wiring. I assume the mechanical units Break before Make?

I don't think I'd mess around with hard-wired swapping of terminals on a boat. The batteries are normally in places you have to stand on your head to get to and if you get an explosion or fire at sea you're going to be treading water.

I THINK (but not totally sure) that the mechanical ACR's are Make before Break. They are ignition protected, meaning they are safe to use in battery and fuel lockers and bilges where explosive fumes might accumulate on a boat. Blue Sea Systems builds and sells most of them and the contacts are hermetically sealed. This is an example of one type they make:

http://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A

[Sunking]

I THINK (but not totally sure) that the mechanical ACR's are Make before Break.

Checked and they are. Got me curious enough to look. They have to be Break before Make, otherwise eventually very soon Make fire before Break. Me thinks Electronic be better. Power loss a little, but I don't think it amounts to anything. Today's FET's foward resistance is extremely low. So low you can hear it. Next time your hear a car stereo coming from a mile away is using FET amps.

[J4mie82]

It's a small cabin cruiser for a canal only 20ft long haha. So no dangerous situations if bring stranded at sea just a long jump or a short swim to the bank.

The batteries are housed below the steering wheel under the canopies and I have a small 9.9hp honda outboard. I have refurbished it and installed the electric but at the moment I can only support a tv and a couple of lights with the charging power I have and the hybrid battery. But I don't want to be in that catch 22 where the boat electrics have cost me more than the boat haha.

I won't connect the batteries directly even with a diode as I xan see to many bad things that could happen.
The batteries are house to next to each other and would take less than a minute to swap the terminals. Will the alternator charge the battery nicely if it cranks the motor?

That way I could swap them over in the morning while I'm having a nice English cup of tea and some muffins haha while it charges?

[Sunking]

I have a small 9.9hp honda outboard. I have refurbished it....... Will the alternator charge the battery nicely if it cranks the motor?

That you have to tell us since you rebuilt the motor. What size alt/gen did you put in it? To be effective the alt/gen should at a minimum provide a C/8 charge current where C = battrery rated AH. So example 80 AH / 8 hours = 10 amps. So ho wmany amps does your boat motor provide and you have your answer.

[ChrisOlson]

Those little Honda's only put out 6 amps at full throttle. I thought maybe the boat had a real charging system on it. Basically, what I would do is forget all the solar stuff, etc.. Just get a couple decent deep cycle batteries for the house power and a new battery for the engine starter. When the batteries get low pull into the marina and plug into shore power.

[ChrisOlson]

It's a small cabin cruiser for a canal only 20ft long haha. So no dangerous situations if bring stranded at sea just a long jump or a short swim to the bank.

I have to ask how long have you been on boats? This is what happens:

http://www.nbcnewyork.com/news/local/port-washington-boat-fire-explosion-manhasset-bay-marina-272050871.html

Swapping terminals around to switch batteries and sailing with known bad batteries is not something any responsible skipper does. So I am saying please don't cobble stuff on your boat. Marine stuff is spec'd, even down to the type of wire you can use, for your safety and the safety of those around you on the water. And it don't matter if your boat is a Dock Queen or sailing the North Sea. On a boat all it takes is one careless move.

[J4mie82]

Haha it said that guy had been on boats his whole life. I have not been on boats long i must admit but English canals are not too deep or very wide.
I was very careful installing the electrics finding the right gauge of wire and tested it all at home first with my multimeter.

The marina does not allow small boats to yse the on shore electrics so was trying become as self sufficient as I can. The solar panel is working out well and every time I have gone the boat it is fully charged up to 14.4v

I'd just like to increase what I have an maybe get a fridge. I'm going the boat today so will see if the house battery starts the engine.
Would I need to remove all the electric appliances before cranking the engine, will there be a high surge of amps?

[ChrisOlson]

Haha it said that guy had been on boats his whole life. I have not been on boats long i must admit but English canals are not too deep or very wide.

The marina does not allow small boats to yse the on shore electrics

Bathtubs are not very deep or wide either, but plenty of people have drowned in them.

I've been to the marina's in Europe in Sweden, the Netherlands and U.K. I know for a fact they let smaller boats use shore power - just that you have to pay for it. It's not free. But it would be cheaper than messing with solar panels on a small boat.

[J4mie82]

Bathtubs are not very deep or wide either, but plenty of people have drowned in them.

I've been to the marina's in Europe in Sweden, the Netherlands and U.K. I know for a fact they let smaller boats use shore power - just that you have to pay for it. It's not free. But it would be cheaper than messing with solar panels on a small boat.

I'm sure they have but that's how natural selection works. I think most marinas do have on shore. This ine does for residential boats but the guy has put up some stupid rules. At the moment if I want to use the electric I have to take my boat to an allocated mooring and pay £5 a day.
I only use the boat at weekends but didn't want the hassle of having to charge the batteries all the time. I will do what you suggest and get a relay once I get a new engine battery.
One last question though.

When I so get a new battery does it have to be of a similar capacity as the 88ah house battery. The house battery is only 3 months old.

Thanks for all your help guys and spending the time to reply to all my questions!

[ChrisOlson]

Ideally your house batteries should be a matched pair. And 88AH is really small for a weekender cabin cruiser. Typically the house batteries are either 4D or 8D marine deep cycles, and those batteries are from 200 to 250AH each for a boat you will be spending the nights on for a weekend. 176AH with two batteries is only 1 kWh to 50% DOD and that's not enough for anything more than basic cabin lighting.

We have a 37 foot sailing yacht and we just spent four days at sea on a cruise to the Slate Islands. We have 860AH @ 24V in our boat, which supplies 10 kWh to 50% DOD, plus a 100A alternator on our Yanmar propulsion diesel for charging when we start it. But we also have a lot of electronics like radar, chart plotter and autopilot that must run 24 hours a day at sea. And we don't waste power at sea running things like TV's because we're at sea to enjoy sailing, not watch TV. If we want to watch TV we do that at home.

Basically your boat is not equipped for weekending with that small of a battery and charging system. And you won't accomplish what you want with solar because when the sun goes down your house battery is going be killed overnight just powering the anchor or masthead/running lights. You need more capacity for things like TV's.

[Mike90250]

.....I'd just like to increase what I have an maybe get a fridge. I'm going the boat today so will see if the house battery starts the engine.
Would I need to remove all the electric appliances before cranking the engine, will there be a high surge of amps?

1) a fridge (small, efficient) will consume close to 1KWh of power daily. That's going to be a couple of armloads of panels.

2) engine starting needs 100's of amps for the starter. That's why a cars headlights dim when you start the engine. Deep cycle batteries are not made to supply a starting surge, so it may not work for cranking the engine.

[ChrisOlson]

If you have a bank of deep cycles for the house batteries they will start the propulsion engine with no problem. A single battery will be stressed out unless it's one of the hybrid type, starting/deep cycle, with thin plates.

When you go adding a bunch of loads to a boat you can power those loads during the day on solar panels. But you have to have the battery capacity to make it thru the night, as well as charge the batteries up the next day again. You can't put enough solar panels on a 20 foot boat to do that. And the little 6A charger in the Honda isn't going to do anything either, as it can run for 10 hours and only put 60AH back in the battery.

If it was me on a 20 foot cabin cruiser being used as a channel boat, I'd just buy a decent battery bank that can make it thru the weekend, maybe with a solar panel or two to help out during the day. Then recharge off shore power at the end of the weekend. Figure out your loads for a weekend and install enough battery capacity to meet those loads to 50% DOD. Then put your solar panels on to help out and keep from discharging the batteries any more than you have to. The reason I would do that is because there is no way you can properly take care of a set of house batteries, even with your solar panels and alternator. They need to be absorbed properly or they'll only last a year. With what you can mount on a 20 foot cabin cruiser for solar power, you're going to need shore power anyway to properly charge your house bank at least once a week. If you had an inboard propulsion engine that you could install a decent alternator on, then it's different. But with a Honda 9.9 you're kind of limited in what you can do.