charge battery from both engine & shore?

[niku]

i am upgrading an older small sailboat that I recently acquired, and have a pretty simple question.

the boat has a manual-start outboard (honda 9hp) that comes with an alternator for charging the battery. currently the alternator is wired directly to the battery with no switching/regulator (I am sure that is bad for the battery?!). there is just a single house battery (no engine battery since the outboard is manual start).

the boat is wired for shore power but just goes to a single AC outlet.

what I need to know is: what equipment do I need to purchase, to allow the battery to charge from either the outboard, or shore power.

of course I need to purchase a battery charger (recommendations?) but in addition ... I presume there is some standard piece of equipment that will allow me to easily switch from charging from shore vs. charging from outboard. even better would be amp/voltmeters so that I can see how healthy my batteries are. best of all would some kinds of sensor to automatically switch back/forth (but of course I can live with switching manually).

also, for safety and extra time between charges, I'd prefer two batteries. so can all of the above be rigged up to two house batteries?

thanks!!!

 

[NYBo]

Re: charge battery from both engine & shore?

Welcome to iboats!

This should work just fine for what you want to do.

 

[Silvertip]

Re: charge battery from both engine & shore?

The charging system on the engine and the shore power charging capability are two entirely separate entities. When you start the engine, the battery which is connected to the engine will charge. When you are connected to shore power, the on-board charger referenced earlier will charge both batteries. To charge both batteries from the engine, you need either a dual battery switch, ACR (automatic charge relay) or similar item. A dual battery switch lets you manually select which battery gets charged by the engine (1, 2, or BOTH). It also lets you determine which battery will power the stuff on the boat. As for voltmeters, you need only one. A simple toggle switch will let you select which battery you want to monitor. If you use a dual battery swtich you don't need the toggle because the meter would be connected to the COM terminal on the switch so it would read Bat 1, BAT 2, or BOTH depending on the switch setting. Most important however, is that you need to determine what the charging current is on that outboard. It is likely quite low so charging two batteries simultaneously is not likely feasible.

 

[Doug N.]

Re: charge battery from both engine & shore?

I would think that the that the charging systems would be auctioneered with diodes so that the higher voltage source would provide the charge current. so, you could leave them both hooked up the battery would charge from whatever source is available. So, for a single battery you don't need anything. When you unplug from shore power only the alternator will be available. When you are on the motor, shorepower will be disconnected. I can't imagine you would be running the motor while on shorepower. Even if you were, the diodes would provide the auctioneer service

Two batteries: If you want both batteries on line at the same time you need to hook them up in parallel (+to+, -to- on the batteries) so that they both will charge and discharge at the same. In that case, you don't need anything special - just make sure there is an auctioneering diode on both charge sources. That would be hard wired in. I can't imagine they wouldn't be there to prevent damage from a battery being hooked up backwards by accident. As silvertip pointed out, charging two batteries might be to much for an alternator on a 9 hp, particularly if the batteries were low.

If you want one battery to be a backup, you need the switch that silvertip described.

 

[bruceb58]

Re: charge battery from both engine & shore?

I would think that the that the charging systems would be auctioneered with diodes.

Not necessary and actually would hurt you because of the voltage drop across the diode.

 

[Silvertip]

Re: charge battery from both engine & shore?

There is no "priority" issue here as to which source is charging. Shore power is obviously not used at sea so the engine does the charging. At the dock the engine is not running so shore power is doing the charging. Both the engine and the on-board charger are protected from each other. The issue is how to charge both simultaneously. Permanent paralleling is one solution but not the best one since the weaker of the two batteries will suck the life out the stronger until both are equal. In this application an ACR is probably the best choice. Depending on what your thoughts are about battery switches, one of those may be the most versatile choice but only IF you are inclined to use it to your advantage.

 

[Doug N.]

Re: charge battery from both engine & shore?

Not necessary and actually would hurt you because of the voltage drop across the diode.

Voltage drop across diodes is negligable. It isn't considered in circuit analysis.

 

[Boatist]

Re: charge battery from both engine & shore?

I like battery isolator with a 3 wire I/O alternator but not a good choice at all with a Outboard.
To start with with a 9 HP alternator not likely your going to be able to charge 2 batteries.
With a Outboard with electric start to use a alternator to charge two batteries thru a battery isolator or two diodes then you have to break out the the charge line inside the outboard. If you do not do this then the electric start will not work because the diode will prevent it.

If it is a manual start then I bet the alternator output is not over 6 amps at full throttle and to charge two batteries with the .7 volt voltage drop accross the diode is just not going to even charge one.

 

[bruceb58]

Re: charge battery from both engine & shore?

Voltage drop across diodes is negligable. It isn't considered in circuit analysis.

Where did you hear that? Of course it is considered in circuit analysis! And it is also significant here. The difference between when the charger detects a fully charged battery and when it is still uncharged is a small voltage and the 0.7V drop that the diode will have is extremely significant.