One or Two start batteris for Twin Engine

[Seevee]

All,


Just thinking about having a dedicated battery for each engine or a shared one for both.


As first, seems like separate make more sense, however, one is simpler.


In either case, you still have the house for a backup. Also, if one wanted more redundancy, use two batteries in parallel for either engine. And you could also hook them to the thrusters for thruster power.



Thoughts?

 

[ScottC]

Hmmm... My first thought is how will you wire the alternators? If you wire only one alternator to charge one battery, and that engine happens to fail someday and you run on the other engine...an issue could arise.

 

[Seevee]

Hmmm... My first thought is how will you wire the alternators? If you wire only one alternator to charge one battery, and that engine happens to fail someday and you run on the other engine...an issue could arise.

Scott,


The alternators would be simple. They would both charge the start and house batteries thru an ACR.


Wouldn't have the issue with one alternator failing, would have the other. And that's extremely rare, regardless.

 

[Chrisjs]

IMO you can never be too thin, too rich or have too many batteries!! Definitely 2 batteries for redundancy - after all that is likely why you have 2 engines and (hopefully) 2 fuel tanks. And just because you have 2 batteries do not go cheap on undersized batteries. You likely need a third battery for the generator, and even more for the bow thruster. That's without even getting to the "house" batteries.

 

[Bkay]

When I had my boat built I asked the very squared away electrical guru about single start battery and he said "no".

I kept pressing why and got a lot of "you'll regret it" and "that's not the best arrangement", but never a tangible reason why. My thought was, like you, one start battery for two engines, one engine alternator going to the start and the other alternator going to the house with an ACR between the banks. I would always start the engine with the alternator that charged the start battery first.

It seemed logical and simple to me. I ultimately agreed to the way they wanted to do it, but I never had a good reason explained to me why it had to be that way.

 

[Alaskan Sea-Duction]

Depends where you cruise. Remote: 2 batteries

 

[ScottC]

Scott,
The alternators would be simple. They would both charge the start and house batteries thru an ACR.
Wouldn't have the issue with one alternator failing, would have the other. And that's extremely rare, regardless.

I have the opposite "problem". In addition to a 48v propulsion battery, I have 4 12v batteries (bow thruster/windlass; stern thruster; house; start). All these batteries -- and only one engine

 

[rslifkin]

On my boat, I went with 2 engine start batteries. Generator shares with stbd engine, although either engine or the generator can be selected to use either start battery. House is separate other than ACRs for charging while underway.

 

[SoWhat]

Port alternator charges port battery. Stbd alternator charges stbd battery. Either one or both can be house battery. Factory set it up that way. Never had a problem. (I also carry a portable power pac for jumping if both are dead)

 

[Pau Hana]

Going thru this right now. I have 3 8D batteries in the engine room; 1 for each Cat 3208TA main, and a third for the genset.

My goat is not weight savings, but simplification. I'm installing a 600aH Lifepo4 house bank, so I figure I can parallel the house bank if needed to start the mains or genset. In 8 years on this boat, we have never had any problems with the start batteries, and I believe 1 8D is more than enough as a primary start battery.

A side benefit will be gaining some real estate back in the engine room.

 

[Seevee]

Peter,



Good point, simple!


And that's my point. I'm not convinced that one needs a separate battery for each engine.



If you wanted redundancy, why not just wire two batteries in parallel, and use for either engine. (We do monitor batteries, don't we, so we'd know if one was going south).


Not, if ALL start batteries quit, I could still switch in the house and start. And, still have a gen as a backup.


So, how much back up and redundancy of the redundancy do we need?


I've never had a battery fail where it stopped me cold in a plane or a boat in the past 100 years..... <g>


Sure they quit, but always had a backup that got me home. Overall, failed batteries have been a minuscule part of the maintenance program. Just not a huge issue.



Just looking for a simple solution. However, I'll keep and open mind.....

 

[Swfla]

Informed personal preference for number of start batteries as long as you can use house batteries for starting backup. Definitely alternators on both engines with ACR.

 

[Bacchus]

My MS 34 single had 3 8D AGMs 1 for thrusters and 2 for combined house / start.
I just finished moving start to the thruster bank to leave a dedicated house bank as part of getting ready for replacements with other than 8Ds but will stay w AGMs as ive had good luck / life with them.
I have gen as back up.
I was originally thinking start & thruster better suited to hi amp start battys and house deep cycle battys.
When I checked w East Penn they confirmed that with (their) AGMs there isnt the usual FLA difference in plate design and their AGM have good performance in both deep cycle and start application. I did note they spec AH and CCA for all their AGM line.
Conclusion & decision made to use GP31 AGMs for all when the time comes. 2 for start thruster bank and 4 for house.
My view of advantages include ability to remove one if a failure occurs vs 2 with 6V GC & flexibility to move battys from bank to bank in case of failure & need to replace multiple batty with new to match age.
I do have ACR for alt charging both banks

 

[ranger58sb]

Going thru this right now. I have 3 8D batteries in the engine room; 1 for each Cat 3208TA main, and a third for the genset.

Woof! An 8D is a lot of battery for a genset!

We gravitated toward a Group 34 for the generator. (Not too different from a G24, I think.) Didn't take much to start our 3-cylindar Yanmar, and even the G34 is larger than what we use in our garden tractor with an almost identical Yanmar diesel.

-Chris

 

[Ken E.]

The setup I have is two start batteries in parallel are used to start either engine. Group 31's presently.

 

[catalinajack]

Yes, perhaps, but what are the chances of that happening? In my opinion, many here worry far too much at the extremely unlikely. Why even leave the dock?

Hmmm... My first thought is how will you wire the alternators? If you wire only one alternator to charge one battery, and that engine happens to fail someday and you run on the other engine...an issue could arise.

 

[catalinajack]

Diasagree. How about no start batteries? I, and plenty of others, use our house bank to start the engines. In the extremely unlikely event that I deplete my batteries overnight to the point they won't start the engines, I can fire up one of the generators to charge the batteries or jumper the generator start batteries. I have gone as low as 25% on the house bank and those eight golf car batteries still started my Lehmans with ease. So, sure, ypu have have starting batteries for redundancy but aall they do is add wiring, switches, and complexity. And, what if one of those switches go bad. No start?

IMO you can never be too thin, too rich or have too many batteries!! Definitely 2 batteries for redundancy - after all that is likely why you have 2 engines and (hopefully) 2 fuel tanks. And just because you have 2 batteries do not go cheap on undersized batteries. You likely need a third battery for the generator, and even more for the bow thruster. That's without even getting to the "house" batteries.

 

[Seevee]

GREAT POINTS.... lots to think about.


I sure like SIMPLE.

 

[rslifkin]

To me, engine start causes a significant voltage dip unless there's a truly massive battery bank involved. So it should be separate from house loads. Generators draw much less power to start, so no reason they need their own start batteries. They can share with engines easily.

I also like separate starting power for my engines in normal ops. Engine start power is safety critical in my mind, so if I lose a battery suddenly to a bad cell or something, I'd like to be able to at least get one engine started quickly in an emergency (and then can flip switches to get the other one started).

For me, each engine charges its own start battery. Ignition interlocked ACRs allow each engine to charge the house batteries, but keep things isolated if that engine isn't running. It's not the simplest setup, but it's not particularly complex. And in normal ops, no flipping switches, no opportunity for user error, etc. Switches are only touched if there's a problem.

 

[Ski in NC]

Tiara boats for decades had twin engines starting off a single bank. They did add a twist to it, one engine alt fed the house bank directly. They did have a manual house/start cross tie in case you lose an alt or similar problem.

It made it a bit tricky to troubleshoot as many operators and techs did not understand the system.

One caveat: With one engine running, starting the second can really spike the amp output of the running engine alternator.

I kinda like the "use the house bank" for starting design. Keep gennie batt sep and if you poop the house bank so far you can't start mains, just run the gen and chgr/inverter a bit.

Many boats already start both engines off one bank as many operators leave the manual crosstie closed.

Simple is better!!! Been on way too many boats where over the years folks have added batts, inverters, switches, cables, etc... And no schematics drawn. Try to troubleshoot one of those and it gets confusing fast.

 

[Bacchus]

I don't Ike having helm electronics powered by start / thruster Betty's. I have had starting causing V drop that affected electronics. I'd much rather have critical electronics powered by a pure house.

 

[markpierce]

Shouldn't each engine have an alternator?

Since one starts their engines one at a time, wouldn't one start battery be sufficient? There are always the house batteries if the start battery fails.

 

[koliver]

4 6vGC house
1 4D Start
Twin TAMD41s, Westerbeke 4.5kw genset, all started by the 4D.
Last change of the 4D was after 11 yrs, so it hadn't suffered.
Never had to use the crossover solenoid in 26 yrs.

Simple

 

[Seevee]

I don't Ike having helm electronics powered by start / thruster Betty's. I have had starting causing V drop that affected electronics. I'd much rather have critical electronics powered by a pure house.

Don,


Agree with that. Did your boat come with house running the thrusters ad did you change that out?


The more I read, the more I like one battery (small bank) for start of both engines and the generator and thrusters. House as a backup.



House deep cycle does what it best does and the high amp start batteries do what they do best.


Thoughts?

 

[Bacchus]

Don,


Agree with that. Did your boat come with house running the thrusters ad did you change that out?


The more I read, the more I like one battery (small bank) for start of both engines and the generator and thrusters. House as a backup.



House deep cycle does what it best does and the high amp start batteries do what they do best.


Thoughts?

Steve
Originally mine had a combined house / start with 2 8Ds and a 1-2-all SW a separate thruster bank 8D and then a GP 24 Gen start. I removed a diode isolator between start & thruster banks and replaced with an ACR in "ignition mode". I also removed a MS installed diode isolator in my shore power to charge the 4 battys w a 3 bank charger leaving gen batty charging to its own Alt. I also changed out my gen on-off Sw to a 1-2-all with same size & bolt holes based on a suggestion from another TFer w a MS. That allowed me to parallel gen w house start with flip of a Sw if / when needed. I used it to connect for charging if I hadn't run gen in awhile but never had an emergency situation that reqd paralleling.
Most recently I planned to install a Balmar SmartGauge to monitor house & thruster bank and they will not work with a pair of swithched battys. I ran most of the time in the All position anyway and never liked the way MS combined house & start. I moved my main eng start to the thruster bank and combined my 2 8Ds for a pure house bank. It was relatively easy with the addition of one wire from starter to thruster batty and I actually reused the unused cable from my house/ start when I combined the 2 into one house bank. By doing that I shortened the starter run and increased the cable size so V drop decreased... win...win
So far I'm pleased with the new set up and really like having the Balmar SG that gives me V & SOC on house and V on thruster battys.
All of the recent mods were in anticipation of needing to change out my 3 AGM 8Ds and not wanting to ever have to handle another one (other than removing these). So far the Balmar shows them still performing well.
I thought maybe I'd go to a pair of AGM 12V GP31s for thruster and 4 AGM 6V GC for house but when I checked w East Penn they told me that their AGMs all have the same plate design and serve deep cycle & start equally well. Im now thinking of using all GP31s which would allow uniformity and ability to drop one if it failed vs needs g to drop a paid of 6V GCs
Long winded answer but the story has evolved over time and I really like the current set up compared to what MS started with.
When I get some spare time I'll write the project t up and put it on my Bacchus website with schematics but likely won't be until snow flies!

 

[Pau Hana]

Steve
Originally mine had a combined house / start with 2 8Ds and a 1-2-all SW a separate thruster bank 8D and then a GP 24 Gen start. I removed a diode isolator between start & thruster banks and replaced with an ACR in "ignition mode". I also removed a MS installed diode isolator in my shore power to charge the 4 battys w a 3 bank charger leaving gen batty charging to its own Alt. I also changed out my gen on-off Sw to a 1-2-all with same size & bolt holes based on a suggestion from another TFer w a MS. That allowed me to parallel gen w house start with flip of a Sw if / when needed. I used it to connect for charging if I hadn't run gen in awhile but never had an emergency situation that reqd paralleling.
Most recently I planned to install a Balmar SmartGauge to monitor house & thruster bank and they will not work with a pair of swithched battys. I ran most of the time in the All position anyway and never liked the way MS combined house & start. I moved my main eng start to the thruster bank and combined my 2 8Ds for a pure house bank. It was relatively easy with the addition of one wire from starter to thruster batty and I actually reused the unused cable from my house/ start when I combined the 2 into one house bank. By doing that I shortened the starter run and increased the cable size so V drop decreased... win...win
So far I'm pleased with the new set up and really like having the Balmar SG that gives me V & SOC on house and V on thruster battys.
All of the recent mods were in anticipation of needing to change out my 3 AGM 8Ds and not wanting to ever have to handle another one (other than removing these). So far the Balmar shows them still performing well.
I thought maybe I'd go to a pair of AGM 12V GP31s for thruster and 4 AGM 6V GC for house but when I checked w East Penn they told me that their AGMs all have the same plate design and serve deep cycle & start equally well. Im now thinking of using all GP31s which would allow uniformity and ability to drop one if it failed vs needs g to drop a paid of 6V GCs
Long winded answer but the story has evolved over time and I really like the current set up compared to what MS started with.
When I get some spare time I'll write the project t up and put it on my Bacchus website with schematics but likely won't be until snow flies!

Thank you for sharing- this is exactly the revision I’m looking to do.

 

[Seevee]

Steve
Originally mine had a combined house / start with 2 8Ds and a 1-2-all SW a separate thruster bank 8D and then a GP 24 Gen start. I removed a diode isolator between start & thruster banks and replaced with an ACR in "ignition mode". I also removed a MS installed diode isolator in my shore power to charge the 4 battys w a 3 bank charger leaving gen batty charging to its own Alt. I also changed out my gen on-off Sw to a 1-2-all with same size & bolt holes based on a suggestion from another TFer w a MS. That allowed me to parallel gen w house start with flip of a Sw if / when needed. I used it to connect for charging if I hadn't run gen in awhile but never had an emergency situation that reqd paralleling.
Most recently I planned to install a Balmar SmartGauge to monitor house & thruster bank and they will not work with a pair of swithched battys. I ran most of the time in the All position anyway and never liked the way MS combined house & start. I moved my main eng start to the thruster bank and combined my 2 8Ds for a pure house bank. It was relatively easy with the addition of one wire from starter to thruster batty and I actually reused the unused cable from my house/ start when I combined the 2 into one house bank. By doing that I shortened the starter run and increased the cable size so V drop decreased... win...win
So far I'm pleased with the new set up and really like having the Balmar SG that gives me V & SOC on house and V on thruster battys.
All of the recent mods were in anticipation of needing to change out my 3 AGM 8Ds and not wanting to ever have to handle another one (other than removing these). So far the Balmar shows them still performing well.
I thought maybe I'd go to a pair of AGM 12V GP31s for thruster and 4 AGM 6V GC for house but when I checked w East Penn they told me that their AGMs all have the same plate design and serve deep cycle & start equally well. Im now thinking of using all GP31s which would allow uniformity and ability to drop one if it failed vs needs g to drop a paid of 6V GCs
Long winded answer but the story has evolved over time and I really like the current set up compared to what MS started with.
When I get some spare time I'll write the project t up and put it on my Bacchus website with schematics but likely won't be until snow flies!

Don,


Excellent write up, and I'm also thinking along the same way. Looking forward to your write up.


Now, I could argue to get "real" deep cycle and start batteries. I could argue that when they combine the battery into a dual use you get the worse of each. I'm not a fan of Penn. Check in to Lifelines or Oasis. Must better stuff. My Lifelines (Concord) are great and the only reason I'd go to the Oasis, is I feel the the newer technology is a better value... and eventually the Lion will be the go-to battery.... just a thought.

 

[Ski in NC]

You can absolutely use deep cycle batts as starting batts, bank just needs to be bigger to get amperage up.

Also, boats often have WAY more starting battery capacity than needed.

When I was doing a lot of engines in my shop, I kept a grp 31 batt that was not anywhere near new, and it started every engine on the bench up to 10 liters (3208), and did it just fine.

When I set up my boat, I put in a single grp 31 as a start batt for both the main (450hp 8.3 liter) and gennie (NL 5kW). Does absolutely fine down to engine room temp of like 40-45F. I do have the house bank I can parallel to if needed. The start batt is not a deep cycle. If I used deep cycle I would put two in there.

House bank needs to be as big as it needs to be for the Ah drains expected. Start batts can be really minimal as long as you have backup.

Some of the new sporties being built around here have 32 liter engines starting off four grp 31's (of course they are 24V). That's 32 liter of engine cranked off something only a little bigger than a single 8D.

 

[Bacchus]

Don,


Excellent write up, and I'm also thinking along the same way. Looking forward to your write up.


Now, I could argue to get "real" deep cycle and start batteries. I could argue that when they combine the battery into a dual use you get the worse of each. I'm not a fan of Penn. Check in to Lifelines or Oasis. Must better stuff. My Lifelines (Concord) are great and the only reason I'd go to the Oasis, is I feel the the newer technology is a better value... and eventually the Lion will be the go-to battery.... just a thought.

I certainly agree if we are tslking FLA... not so sure for AGM. As I said I originally was thinking GP31 start & GC for house but E Penn said no performance difference. You could take that as they do both well or do both poorly? The design details are beyond my expertise so can't debate it from personal knowledge and have to go with mfg recommendations.

I guess I have become a fan of AGM and feel they are right for me, my use and budget. Nothing against others that feel Li-ion are the "best" or Lifelines are "better". I dont need a Cadillac if a Ford or Chevy will do the job. For the $/AH and what I have experienced for life its the sweet spot for me. I doubt the Lifelines will outlast the E Penns by a factor of 1.5 - 2 X to break even. Like I've said before my AGM 8Ds have completed 8 seasons and still serving me well and at $500 Ea I consider them a good buy... and they have been in both hi amp (thruster) and deep cycle positions (house)... waiting to see which fails or shows signs of weakness first??
At $180 for their GP31 (800 CCA & 105 AH) I think they are a good batty... I'm sure there are " better" out there but at what premium on an AH basis?
Just my opinion & decision and others are welcome to theirs... no hard sell here.

 

[Dougcole]

Hey Steve,


I'm far from an expert on this, and would certainly bow to Don and Ski's superior knowledge, but since we have almost exactly the same boat, I will tell you about my setup so you can use it for data. Only difference is that I don't have a thruster.


Our boat was factory when we bought it, that is 2 8D, each started an engine and the house loads were split between them. I don't like that setup for a cruising boat and wanted more capacity for the house bank.


So about 6 years ago I changed to 4 6V GC FLA batts for the house and a 4D to start both engines. I just moved all of the house loads from the stb engine to the port (house) bank, then ran both starter wires to the stb (start) bank. I put an ACR between the two banks. So both alts run to the start bank then through the ACR to the house.


It has worked pretty well, though I didn't get as many years (5) out of my house bank as I expected to. My start batt lasted about 6 years before it failed as well. I replaced my house bank with 4 more GC FLA and the start batt with a group 31 FLA. It fires both motors right up. I also added a victron SOC monitor, so I now have a better handle on what is going on with my house bank. It is not connected to the start bank.


I upgraded my genset batt to a group 27. I'm pretty sure it would start my mains in a pinch. I have one leg of my 3 leg 50 amp shore power charger dedicated to the gen set batt. I got tired of it going dead if I let it sit too long.



I really like Don's idea of having the genset batt on a switch that allows it to be paralleled with the main start batts.


Admittedly, it's not the most sophisticated solution. I'm not real clear on how well both alts play together when charging, but my SOC monitor shows plenty of juice flowing into the house bank when the engines are running, so I know it works.


I'll probably go to AGM's when I replace my next set.



Hope that helps.


Doug