Yet another dual Batt question

[carcraze]

Okay I haev my new to me boat in the water and am trying to figure out this battery wiring the last owner had going on.

I have had dual Batts to a single motor which is pretty straight forward. This has twin engines as well yet he is running 2 batts and 1 batt selector switch and as I side note there are 2 altermators.

When I hook up just the right batt nothing will work. Hook up just the left batt and power is had on select batt 1. Hook up both and I can select between batts, I beleive it is selecting anyhow.

The left batt also has a Pos lead directly to the starter post. While working on a broken oil sender wire I had the right engine harness unpluged and had nothing on the dash working from either Batt so I am assuming the dash control is from the right engine harness.

The left cranks very well which would make sense as it has a short lead from the left Batt to the starter post. The right engine cranks very slowly with new Batts and the Pos lead is getting warm. It does not have a short lead from the Batt to the starter post as I assume this would render the switch useless. The lead is a pretty long run from the right Batt to the switch and then back to the right starter post hence some of the heat and voltage drop.

Mind you with the direct run on the left Batt to the left starter post not sure you could ever not start that motor from that Batt.

Does anyone have a wire diagram for a common setup with dual Batts, twin engine and only 1 switch?


Hope some of this makes some sense as I have not drawn it out.

 

[Silvertip]

Re: Yet another dual Batt question

Twin engines with dual batteries should not even have a switch. Remember, standard dual battery switches have ONE INPUT (from the alternator) and TWO OUTPUTS (one to each battery). They have OFF, BAT 1, BAT 2 and BOTH settings which allows the SINGLE alternator to charge either or both batteries depending on how the switch is set or to kill electrical power to the entire system. It also means all loads (except perhaps the automatic bilge pump) are connected to the COM (output) terminal of the switch which then means you can select which battery (or both) will power everything. Any wiring scheme that allows two alternators to commonly feed any one or more batteries without some form of isolation means you have two regulators fighting for control. Yamaha for example does not recommend this configuration at all.

I see no need for a switch in your application. A set of jumper cables would work nicely if you experienced a dead battery. Without a wiring diagram (crude is ok) I won't even take a stab at what you have. If you had a separate house battery (third battery) thats a different issue and I can help with that.

 

[carcraze]

Re: Yet another dual Batt question

Thanks for the response, this is crude at best. I am looking at this thing scratching my head. I could see using 2 switches with some form of isolation or alternator balancing circuit but this is a mess.

Some of this is assumed at this point as I have not traced everything out, I do know if you unplug the right engine harness I loose dash switches, blower ect.

I know each key powers the associated engine gauges.

I have direct wired a float switch to the right eninge batt for the bilge while slipped. The other problem I have if I leave the switch on I kill the batt within a couple weeks but would really like to power the merccathodes while sitting but I have not checked the power draw from them to see if the batt will maintain through a few weeks.

This is the best I have.

 

[Silvertip]

Re: Yet another dual Batt question

What a good way to hose up a perfectly good system. However, from what you've shown here is what this system provides.

1) Right engine won't charge the right engine battery when the switch is set to the left battery, but it will charge the left battery at the same time the left engine is charging it. This is totally unnecessary and not even recommended.

2) The scenario in #1 is reversed when the switch is set to the right engine battery position. As in #1 this is also unnecessary and not recommended.

3) Both alternators charge both batteries when the switch is set to BOTH. Again there is two alternators working in tandem and not recommended. Two batteries being charged by two separate alternators will not charge faster than two batteries being charged independently by two separate alternators.

4) OFF does not kill the left engine electrics.

5) If the switch is left in the BOTH position the batteries are in parallel and the weaker battery will draw down the other until both are equal.

6) The only advantage I see to this switch is when operating on one engine or the other you have the option of the charging both batteries. So you have one positive and five negatives. You need to determine what this system is really worth to you.

Recommendation: Ditch the switch and carry jumper cables should you need to jump one engine from the other or temporarily parallel the two batteries. That can be done by the way with a simple ON-OFF battery switch so you either parallel the two batteries (as with jumper cables) or not. When OFF the system is totally isolated to each engine. When on the batteries are paralleled and you don't have the NO CHARGE scenario you have now.

 

[carcraze]

Re: Yet another dual Batt question

I agree with the hose up comment.

I was considering seperating the systems, the drawback is I would not be able to isolate the Batts from the system and I fear they may die after a couple weeks as that happened leaving the system on before.

Here is what I would like it to do.

Be able to power the system from 1 Batt while we are out and not running as the boat has a fridge, not sure how it is fed yet though.
Use 1 as a boost in case of running one down (the parallel will work here) and charge all Batts when needed.
I really would like the Mercathode system running on both drivs whil in the water but I do not have shore power or a tender at this point and I am not sure how much they draw in amp hours?

I thought about tieing the 2 starter posts and removing the left motor Batt tie in but that would not solve the 2 Alts charging either Batt or both without something to prevent the Alts Regs from running together.

Thanks for you help, I have a mess like so many other systems I have found on this thing from an owner that new enough to be dangerous.

 

[Silvertip]

Re: Yet another dual Batt question

Why do you feel the batteries will die by being separated. Having one battery on each engine is no different than the single battery on your car or truck. If the batteries are discharging something is drawing current. The way to stop that is to find what is doing it (such as a bad diode(s) or regulator in either or both alternators. If you have an electric fridge on board you need a very large deep cycle as a house battery. THEN you can use the switch to power things however you like without the issues you have now. I did forget to mention that the two batteries have their grounds isolated currently so that may be why you having an issue. One engine cannot charge the opposite battery if the ground terminals on both batteries are not tied together. If there is a jumper cable between engine blocks, that connection would indeed exist (but it doesn't show on your diagram so I mention it here).

 

[carcraze]

Re: Yet another dual Batt question

Thanks for all your help Silvertip.

I searched for a large grounding lead between both blocks and could not find one while I was trying to figure out what this previous make shift system was doing.

I do however suspect (not confirmed) that there may be some type of ground tied together in the dash that may be from each enigne. I was checking some grounding issues on the thermo housing and recall seeing a ground path to both engines. I need to confirm this as well.

I understand having the Batts tied in is no different then a car system but I did leave the Batt on and it was flat dead (reading 2.3V) inside of 2 weeks while sitting on the trailer. I have yet to find the fridge wiring, I am going to pull it out to determine if it is switched or on all the time the Batts are on at least from the right motor. I have been frying larger fish on it since I bought it sort of speak. I am going to throw a current check on the system see if I can find it. I do know the 2 merccathode systems have to draw something, you don't happen to know their draw and if they will draw a medium duty marine Batt down in a couple weeks do you?

If I seperate the 2 systems back then most of the lights, radio, and accesories I suspect will be fed from the right Batt. If I do tie the block grounds together then I could use the switch as a single position to tie the 2 Batts together for emergency capacity for starting. Do you know if tieing the blocks together would have any ill effect? My electrical background says it should be fine as long as the Pos side is not connected unless jumping is required.

Then I guess next year I will determine if a house Batt is needed depending on how much the little woman wants to stay out, as it stands she says she does not think overnighting is her thing.

Sorry for all the stupid questions.