Two Engines - How Many Starting Batteries ?

[bill good]

Thanks I'll turn it back to Sono & work more on the suppliers of these "new" AGMs Will post the results when available. Yanmar still supply new 1GMS with the same 14.1v constant votage auto type alternators.
I still believe the stepped regulator or some means to reduce the voltage to 13.6-13.8Volts after the initial recovery is needed for max battery life.

Regards Bill Goodward

[Sonosailor]

Well, it looks like six to one for using only one battery for starting both engines, as long as I can maintain the emergency switch to connect the house batteries when needed. Thanks folks.

In response to some of the other comments:

Presently all 3 banks are served from the two 55 amp alternators through a diode block (two connectors in, and three connectors out). Presently all 6 batteries are on a shelf over the inboard side of the port engine. I have had no more trouble starting the starboard engine than the port over the years.

The diode block does appear to remove about 0.8 volts, but I am using the stock regulator on the alternators, with the sensor wire connected to a switch that can allow me to choose either side of the diode block. This way, at least when I'm using only one engine, I can choose to allow the regulator to be governed by the voltage at the battery, and therefore it ramps up the voltage a little higher. When I use two engines and let them both sense the batteries and each other, the alarms come on - the alternators don't seem to want to know about each other. Interestingly, once both engines are running, the alarms stop and all is well.

I've read a lot about batteries, but seem to have missed how a slightly higher charging voltage might shorten their life. I'd like to hear more from Bill on this. What is your source of information on this?

The solar panels and wind generator bypass the diode block, and trickle into the batteries with their own regulators. As stated, a switch on one panel's input allows me to move it between banks. I'm quite happy with this, and while cruising the wind and sun become significant sources of our power. I have two Sharpe 123 watt panels, providing up to 7 amps each, and an Air-X Marine windmill that is fused for 30 amps. I am presently working on a panel that will provide a separate "Blue Sea" amp meter for each energy source. I know you can get meters to switch from one source to the other, but I think I'll enjoy the KISS system and being able to see all at a glance.

My shelf is configured to hold the standard 12 volt batteries, so I'll have to do some measuring to see if I can switch to 6 volt batteries.

Thanks again for your input, and feel free to continue to comment.

[hellosailor]

Bill-
You may very well be right about the lower voltage, but without knowing the battery specs, the exact regulator/alternator ouput (i.e. the automotive type fold back their outback power radically as voltage comes up)...who knows?

Sono-
" the alternators don't seem to want to know about each other." I would suspect that. Common auto type alternators are designed to work solo. You'd probbaly do better to replace one with a single alternator of a larger capacity, use that as your sole alternator, and leave the other one disconnected as a backup. Usually if you disconnect the alternator totally, or at least disconnect the field wire, you can leave it belted up and spinning with no real loss, if unbelting it is an issue.

A diode block is problematic, even with moving the sense wire. You start with overworking the alternator since it is now trying to put out 0.8V more than it would without the block. That may not sound like much--but it is significant for a device that lives and dies in the narrow 13.8-16V range. (13.8 being very low, 16V typically being an overvolt failure and burnout).

And of course if you only have one alternator sense lead, but there are multiple battery banks, no matter where you connect that sense lead you are going to be mistreating all but one bank--at best.

Combining all that with solar sources as well...I've often heard people ask if there's any one controller that will handle them all with aplomb and never quite heard an answer to that. It seems that splitting up the system options, so one source can charge one bank while another source works with a separate bank, may keep the electronics happier, blissfully ignorant of each other.

[roblanford]

OK, lets compare the 2 options:

1. Buy 6 new batteries of the capacity you need.

or

2. Buy 6 new batteries, buy additional switches, separators etc., modify existing wiring.

What do you gain for all the extra expense and work? Nothing, in fact you loose the safety of having 2 starting batteries.

The aircraft analogy doesn't work because if your 4 engine plane won't start you call the mechanic to fix it.

If you are sitting in a cove 100s or maybe 1000s of miles from help and your starting battery craps out and you have run your house system down, you're screwed. Even if you can start your engines off the house bank, your 1 and only starting battery is D.O.A. and needs to be replaced. Then think about if you had the failure in a life threatening situation.

I wonder if management at Fountain-Pajot knows that their systems engineers are obsessive compulsive for designing all their cats 35' and larger with 2 starting batteries, and that Hellosailor is smarter than all of them.

You have the right system.

[hellosailor]

"The aircraft analogy doesn't work because if your 4 engine plane won't start you call the mechanic to fix it."
Robert, I knew a fellow who I'm sure has passed on by now. He was a marine aviation mechanic when I knew him, and every one of his tools (many brass/bronze so they couldn't make sparks) had a hole drilled in it, to attach a lanyard to.
He used to work on flying boats, and the lanyard was because "it can be so damned frustrating to drop a tool in some lagoon and see it sitting on the bottom, a hundred feet beyond your reach." No, you can't and don't always call in a mechanic for an aircraft, sometimes the mechanic and the spares have to be flown in from far away at great cost--just like boat parts.

But as the commercial aviation industry has shown, having fewer engines on each airplane means fewer engines to break down--and greater reliability by having LESS redundancy.

FP may have their own reasons for their designs, having nothing to do with anyone else's choices, or priorities. Most manufacturers build whatever sells to the greatest market at the greatest profit--and engineering is NOT the rationale for the way they build things. Marketing is.

[fastcat435]

One starting battery will work fine but 2 is safer.
We use 2 x 40 Amp AGM batteries each weighting 9 kilo,s for both the engines
these can be connected to the house bank if nessecary and can via a loop be conneted together as well Via A big V
The service battery,s are under the seating in the saloon and each of the starting batterys are next to the engine rooms nice and very short wirnig decreases resistance, Electrical connections are made directly to the house bank with possibility,s to connect one starting battery to the other or to the starting battery and to the service pack.
That way we can charge or start from any battery source and our solar panels keep all units full even when gone for a long time

[hellosailor]

"40 Amp AGM" Oh, motorcycle batteries. [g]

I know the 12v 17AH AGMs are used in most of the commercial "jump start" boxes that are sold here in the US, and I've used a 17AH battery to start a Volvo MD7A, but when I think of SLI batteries on a boat, I usually think of something a bit larger. Then again, I guess if the engine is only around 7hp it doesn't need much of a battery to spin it up.

Still, two starter batteries plus a house bank is triple redundancy. One hopes that is more redundancy than the average non-astronaut would need.[g]

[44'cruisingcat]

One start battery plus the house bank as backup seems to be SOP for most single engined boats. As long as it will start either engine effectively, it should be fine for twin engines at least 99% of the time.

Fastcat, I was under the impression your boats had electric drives, but you mention starting batteries - are the electrics an option?

[fastcat435]

Hallo 44' cruisingcat
no the price for electric drives or diesel saildrives is the same but we also use diesel generators and for these we also use a 40 AH hour ultraligth AGM battery , these battery,s are actually made for Ultra ligth aircraft but they work great for us a low weight , only 20 LBS each and a 500 amp cranking power good for diesels up to 40 HP
Electric retractable are an option while electric inboard are the same price as diesel saildrives

[lowride14]

I am in this thought process for my boat as well. I would say

-1 good starting battery,
-and how ever many house batteries you want. -and for a third backup i would keep one of thous booster packs around, and make sure it stays charged,
-as for a fourth backup really long, heavy gauge jumper cables.

dont get me wrong, if no other boats are around jumper cables arnt going to do squat unless you make some coconut batteries to jump off of. but it makes it alot easier to borrow someones else power if you dont have to disconnect batteries and pass them over board.

and when someone comes to you for help, its much easier to hand them the jumper pack.

I would also just to be safe, keep a small cheap solar battery maintainer on the starting battery.

I love to be prepared, not just for me, but I love to help others.

[Steve Strand]

For a number of years now, we have not used a dedicated starter battery, just used the house battery bank to start the engine, this was done on our last several monohulls. There is so much amperage in a house bank that the starter turns over just fine even if the voltage is down a bit. I know this is really unconventional, but it has worked for us for the last 15 years without a single problem.
Steve

[svcattales]

Originally Posted by Steve Strand

For a number of years now, we have not used a dedicated starter battery, just used the house battery bank to start the engine, this was done on our last several monohulls. There is so much amperage in a house bank that the starter turns over just fine even if the voltage is down a bit. I know this is really unconventional, but it has worked for us for the last 15 years without a single problem.
Steve

Steve, I'm with you. I have 4 golf carts to starboard and 2 to port. The port 2 batts are paralleled with starboard batts with a manual switch so the two sides can be isolated if there is a problem. Basically, there is one house bank with 6 golf cart batteries. I have used this setup in my cat and previous monohull for 10 yrs and always have the amps to start engines. I do watch the voltmeters closely and have wind & solar available if I really screw up.

In my monohull I followed the separate starting battery convention for several years and replaced the start battery annually because it was over charging. Voltage reg was sensing off house bank that needed charging and "cooked" the engine battery which stayed fully charged.

Sono, Great boat name!

[tsmwebb]

Originally Posted by Steve Strand

For a number of years now, we have not used a dedicated starter battery, just used the house battery bank to start the engine...

We do it that way too. Works very well, IMHO. We keep a small emergency starting batter on it's own charging circuit.

Tom

[SeaKing]

Good thread to bring back to life lowride14. good fact about the ultalight AGM batteries by fast cat.

Our setup has a group 27,92 Ah, 810 MCA for engine start and 4 Group 24's, 79 Ah batteries for the house on each side of the boat. That gives 640 Ah's for the house total. I can start the engines from the house batteries if needed. I now have all AGM batteries.

The previous owner had regular batteries for the start batteries and gel's for the house. The problem is they live under the bed's in the aft stateroom's. Worse yet the surveyor didn't catch it at the survey. I realized they were there not long after we got the boat and got 2 new AGM's immediately.

I want to add 400-500 watts of solar on top of the boat now, we just made a nice hardtop/ platform for panels this past year. I am lusting for big panels.