recharging 2 battery system

[Plandeck]

Anyone know where to attach an isolator relay switch between 2 batteries so both of them charge when my 8hp Nissan outboard is running? Sailboat has two batteries isolated from each other. One starts the motor. The other powers the boat lights etc. Thus only one battery charges up when motor is running. Where on the motor electric system can I hook up my "Stinger" solonoid relay switch that will connect both batteries together when the motor is running so they both charge? Will the wire from the rectifier to the starter switch work? Motor is tiller model.

 

[pvanv]

Re: recharging 2 battery system

You have a challenge, and we need a little more info to help much.

Since you have a Tiller motor, it is magneto-ignition, and hence does not have a 12v "ignition" wire to trigger the solenoid, so no way to do what you ask. In that case, you need an ACR (such as from Blue Sea Systems) to auto-combine banks without a trigger wire. The rectifier output will be "hot" whenever the battery is connected to the battery, so that won't work... the stinger would constantly be energized, which has the same effect as having a single battery bank, except that the stinger relay coil will be using some power all the time, draining the batteries even when the motor is off.

If you had a Remote model, there is 12v switched power available at the key switch inside the RC box, which is hot whenever the switch is turned to "on" or "start".

Even so... the 8 hp 2-stroke motors only make about 5 amps on a good day at WOT, and make almost nothing at idle. The NSF8A3 4-stroke makes about 6 amps at WOT, and makes a few amps at mid-range speeds. So, the amount of charging that you would get from the outboard is minimal. These charging systems are essentially intended to replenish what power was used to start the motor, and not much more.

A simpler system for outboard-powered sailboats is to run a single battery bank (or set the battery switch to "both" when running the OB). In the case of a single bank (which could be 2 paralleled batteries), since the OB uses very little power to crank, you should be OK unless you really run the battery nearly dead with the cabin lights, etc... If you do, you can pull-start the OB.

 

[Plandeck]

Re: recharging 2 battery system

Thank you for the reply. It's what I was fearing based on the wiring diagram. I had a problem one season sailing all night with the lights on, in the early morning hours approaching harbor I went to lower the outboard (Honda with power tilt). Alas there was no juice left in the battery to operate the tilt hydrolics! Motor could not be lowered, and in the wind, waves and dark doing it manually was impossible. Needless to say, I am still hear, but sailing into a new harbor in the dark with lights everywhere and plenty of wave action was not a small act of bravery. Now I feel its important to separate the motor battery and the accessory battery, even with the pull start option. Incidentally, installing the electric solonoid choke could present the same problem as above since it won't operate without current right? I get a little less than 1.5 amps at idle...not enough to recharge drain from an autopilot etc especially since I only motor out of the harbor and back in.

 

[MattFL]

Re: recharging 2 battery system

For future reference, the hydraulic tilt most likely has a screw that you can turn to manually open a pressure relief and lower the motor. You might have to get wet to do it, but it's an option.

 

[MattFL]

Re: recharging 2 battery system

After rereading the original post, it sounds like you need a Standard automatic battery isolater.

 

[MattFL]

Re: recharging 2 battery system

Like this, but the marine version:

NOCO IGD90HP Grey 90 Amp High-Performance Battery Isolator:Amazon:Automotive

 

[Plandeck]

Re: recharging 2 battery system

How about adding a one-way diode between the rectifier and the starter switch? This way only current moving from the rectifier (ie when the alternator is charging) will reach the "stinger" relay switch and link the batteries. When the motor is not running, current from the battery will be prevented from moving past the starter switch towards the rectifier and activating the stinger relay. See attached diagram.

 

[pvanv]

Re: recharging 2 battery system

How about adding a one-way diode between the rectifier and the starter switch? This way only current moving from the rectifier (ie when the alternator is charging) will reach the "stinger" relay switch and link the batteries. When the motor is not running, current from the battery will be prevented from moving past the starter switch towards the rectifier and activating the stinger relay. See attached diagram.

Might be interesting. You would need at least a 10-amp diode... and you would lose 0.7 v drop across it. Instead of that, you could open the charging wire (where you have the diode in your diagram), and route the charge wire through a fuse to both the stinger trigger and the charge terminal of the relay. Or just use an ACR from Blue Sea Systems.

 

[Plandeck]

Re: recharging 2 battery system

That's what I thought. Why do they route the rectifier back through the start switch anyway? Thanks

 

[pvanv]

Re: recharging 2 battery system

That's done so you don't need a separate charge wire... just connect the 2 wires to the battery and go... but if you need to isolate the 2-bank battery setup with a stinger trigger, you will want to separate the charge wire from the battery harness (to trigger the stinger), and you will need some sort of diode or relay to keep it that way (not tied to battery voltage directly), otherwise the charge wire will still be at battery voltage all the time.

 

[Plandeck]

Re: recharging 2 battery system

...I use the stinger instead of the other options because I run the auxilliary (automatic) bilge pump through it (for obvious reasons considering my modifications) so if it should need to kick in, it would set off the stinger and have both batteries to power it. Problems with this (1) when motor is charging and sets off stinger it would also set off bilge except there is another diode (3 amp ok?) to prevent current reaching the bilge switch (2) stinger solonoid uses more power than its worth and drains the battery either when charging or pumping bilge...any idea what the amp draw is on the stinger solonoid?

 

[pvanv]

Re: recharging 2 battery system

Not sure about the stinger. We typically use very low draw ACR units from Blue Sea Systems...