Boat Battery system ovehaul - thoughts please

Hi Guys

Further to my previous post I have been doing more work on laying out and overhauling my electrical systems on my 40ft boat. Sorry this will be quite a long post.

My aim is to have 1 crank (1000cca) battery per motor (330hp 6BTA's) 1 genset start battery (small 70ah battery) and 8x 100ah house batteries split into 2 banks (left and right hand banks) - may consider reducing this to 6 batteries to help with charge rates - advise will be welcome.

OK below is a diagram of what I propose.




Hopefully you can see the detail and the notes. (excuse symbols as they may not be correct due to time constraints)

My main areas of concern were / are:-

• 800ah house bank - split into 2x 400ah parallel banks of 4 batteries. These banks are then paralleled to make the 800ah capacity total. output cables will go to a single point (either before or at the battery switch) to maintain same lengths on the cables - likewise the negatives will be grounded using the same length cable. I will pull + and - from opposite ends of the banks to help balance. I have researched this layout and can find nothing discrediting have 2 parallel banks of parallel batteries. - Thoughts?
  
• I wanted to use my 60amp 3 output charger to charge the house bank and the cranks. I couldnt do this with the VSR in 'normal' mode so it has an ignition sense so that it only operates when the ignition is on. When engine is off the 2 charger outputs are separate. When the engine is running, in theory the crank will charge and then open to the house - my only unknown (hence my post to persons far more knowledgeable than me) is if the house is depleted after a few nights away - the alternator could potentially dump 100+amps into the house bank via the crank battery - i'm not sure it works like this, but the crank battery certainly could see sustained high voltage when it only needs float - Again your advice would be welcomed.
• based on only having 60amps output from the charger (if the cranks are full it can output the full 60amp to the house battery) is 800ah overkill? or should I just have 6 house batteries and add the crank batteries in the LH / RH boxes along with the house batteries (frees up storage - saves 50kg and potentially shortens the cabling) all lighting is LED - albeit quite a bit of it- no inverter (yet) no real heavy usage other than the fridge (12/240v Engel upright - potentially 25-30ah per day) - I do have a chest fridge (converted from a freezer) which is incredibly efficient but 240v only - I may add a small inverter to power this but again from research it may only use 20-30ah per day even with the inverter in place. - Thoughts?
• I am assuming all negatives are common on the boat? So if i want to add a shunt for house only ( I have a wireless meter on its way) - I need to run the negatives (from each house bank) to the shunt terminal as a common point and then from the shunt to the 'ground' point?
• Finally - a contentious issue - the windlass - should I run it from the crank battery or the house bank? I honestly have no Idea where its connected to currently. I believe the schools of thought are that its only used while the engine is running - so crank is fine - others think it doesnt matter. again thoughts appreciated!

If you see any other issues with the above - please feel free to point them out.

Thanks in advance

Steve

 

The first thing that comes to mind, is that you need some way of charging the house batteries with the alternators. That can be done with diodes.

 

Hi Gonzo

The VSR takes on the role of the Diodes, without the voltage loss and in an intelligent manner (ie voltage based operation) - the charge is through the starboard engine via the crank battery via the VSR (hence my concern about the crank charging when the house is low)

Steve

 

Yes, if the house batteries are really low, they will discharge the starting battery. At the extreme they will act like a short and damage the starting battery.

 

In theory - the vsr should control that behavior as it should turn off if the crank gets too low, therefore stopping the house draining everything the crank has before charging - again any info is vague so im not 100% sure. I'd also not look at taking the house bank anything below 50% dod - and in practice over a weekend i'd be surprised on 800ah if we got to 30% usage.. may be different with the 600ah bank though.

Steve

 

Does the VSR have a current limiter?

 

Nope but its only rated to 120A which should be fine as thats around what the alternators are.

Steve

 

I had to think about your situation for awhile. If you are using a smart charger the charger should sense the state of charge for the three banks and taper the charge to each appropriately. It should go through bulk, absorption and float and maybe an equalization routine if you're using flooded batteries and it has that capability for each bank. As a practical matter if your charger senses your big house bank is 50% depleted almost all of your charging output will be directed to the house bank and the starting batteries will get little until the house bank comes up in the charge routine. I don't believe that your charger would damage your starting batteries so long as it is working properly. A dual sensing VSR (I'm used to them being called ACR's or automatic charging relays) isn't necessary for the charger. Since you have three outputs you can send charge to three separate banks, house, port start and starboard start. You can verify what I've written by using a multimeter.

But what about the alternator(s)? As I see it, that is where you need an ACR (or dual sensing VSR). It will combine the batteries (in your diagram the starboard start and house bank) when your engine is running and disconnect them when your engine stops and charging current from the alternator stops. The ACR/VSR won't send more charge to the bank that "needs it the most", it will just combine the banks when it senses charging current on one side or the other (wherever the alternator output is connected). You can't overcharge your starting battery because the ACR/VSR combines the house and starboard start battery into one big bank. I'd consider a second ACR/VSR for the port engine. This would enable you to use the alternator output from both engines to charge your house bank.

One more thought. You do have a choice of where to send the alternator current first. If you run your boat for relatively short periods of time and the shut down, you'd probably benefit by connecting your alternator to your starting battery. This insures that you have maximum charge for starting BUT you run the risk of depleting your house bank if you use a lot of house loads. If you run for relatively long periods of time (traveling) you might benefit by connecting your alternator output to your house bank. There can be issues with inrush currents (for short periods) that can cause ACR's to cycle. When I designed my system I had to do some experimentation until I discovered that connecting the alternator output to the house worked best for me. See cycling article below.

Hope this helps. I use a Xantrax charger, a high output/low RPM alternator and an ACR from Blue Sea Systems.

Triple Battery Bank Management Panel - Blue Sea Systems https://www.bluesea.com/products/8689/Triple_Battery_Bank_Management_Panel

Preventing Cycling in Battery Combiners, Voltage Sensitive Relays, and Automatic Charging Relays - Blue Sea Systems https://www.bluesea.com/support/articles/Charging_and_Charge_Management/527/Preventing_Cycling_in_Battery_Combiners_Voltage_Sensitive_Relays_and_Automatic_Charging_Relays

 

After sleeping on this I had another thought for you. Starting batteries and house battery banks have quite different charging requirements. Your house bank is vastly larger than your two starting batteries. I run a single engine boat but most of my friends have twins. They run both engines almost all the time. I'm assuming you do the same, 5teve. Consider moving that VSR to a location between the two starting batteries. Or, you could eliminate it altogether and just parallel your two starting batteries into one "start" bank. Or, you could use just one good battery for starting purposes. You don't start both engines simultaneously, right? When the port engine is started the starting batteries (or battery) will be charged. Assuming the port engine has a "stock" voltage regulator, the charging routine will be perfect for starting batteries. It will be just like an automobile charging routine. The output from your starboard engine alternator could be run through a three stage or "smart" voltage regulator. It will connect strictly to the large house bank. See the link I'll post below. Your house bank will charge much more efficiently this way, much more quickly. You could install a switch between the house and your starting batteries so you could combine them in the case of an emergency. If it were me though I'd just throw a set of jumper cables in the engine room, they would serve the same purpose. You're spending a lot of money on that house bank, this approach would treat those batteries right and maximize their life. BTW, if it were me I'd just make your house one battery bank. Splitting it just complicates things. You might throw a spare alternator in the boat just in case you're out somewhere and you need it.

http://sterling-power-usa.com/Advanced regulators waterproof.pdf

 

5teve I would forget the whole starting battery ideea. Just add that volume and weight to the house battery bank. It's big enough to start the engines even at 50%DOD. If you are really concerned about redundancy fit a hydraulic or spring starter to one of the engines. That will allow a black start with muscle power alone. Air starters are another option but bulkier with all the associated plumbing, tank and compressor.

 

I'm interested in hearing thoughts on missinginaction's post #9. This is the solution I'm contemplating for the same problem - it seems simply and most logical.

Regarding the windlass, I too am considering powering it from the house bank rather than from starting or a separate battery bank.

 

The simplest and most logical is to have one battery bank for everything and non-electrical starters for backup. It's also the lightest and safest option. Most people don't take it because they are not even aware of this option. The choice of mechanical, hydraulic or air starters depends on the space and already present systems available. Mechanical starters usually mean a flywheel housing with an extra starter pocket since most people want to retain the convenience of push the button starts instead of going below and wind the spring by hand. Hydraulic starters can replace the electric starter. The piston accumulator can be small or large depending on how many trys you want before recharging and this can be done three ways: from an engine driven pump, electrical pump, and manual pump. Air starters are practical if the boat already has a compressor with a separate motor. They also completley replace the electric starter.

The next best thing is post nr. 9. Keep the starter batteries on their own charging circuit with small auto alternators, and charge the house bank with big heavy duty marine type ones. I would put one of each on either motor if taking this option. Dock or generator charging can be done with individual chargers adapted to battery size and type.
Windlass instalation depends more on your ability to run really thick cables. The best option depends on vessel size and battery bank location.

 

Hi MIA

Thanks for your replies - as my original post may be a bit vague I will reply to your post by quotes - I hope you dont mind but its easier to address.

The charger is a 3 / 4 stage starter - 60 amps total output over 3 output (1 unique, 2 linked) each output is programmable as to type and max output / float output including voltage and current. You are right - it outputs as much as it can to the most depleted. The equalisation only applies to the flooded on it so shouldnt happen as the batteries are calcium / agm

I am aware that the VSR is not useful for the charger which is why the VSR is set up to only operate when the ignition is on (and in theory shore power is off) The diagram should show the outputs of the charger to each bank.

This is why the VSR is there - this removes the current 3rd alternator which is a) low output b) badly wired) and c) on a not very sturdy bracket (all courtesy of previous owner) I was worried about the alternator charging the crank first then the VS opening and finding that the house bank was 50% so dumping charge current and voltage into the house and crank for an extended period - the saving grace here may be that being a calcium start - it has a very wide range of charge voltage (according to bosch)

Re the second VSR - I would love to (at they are pretty cheap) but I thought to run 2 alternators together you needed a combiner to sync them? Otherwise the alternators sense each other's voltage and mess around with the regulator?

Correct - My priority is start to ensure I can crank - an in theory yes I could charge the house first but generally the crank batt will be full in minutes so house should start charging pretty quick. General run would be 2-3 hours in a day with genset running once engines off - maybe for an hour or 2 also. Its certainly something I can mess around with.

I'm sleeping on this alot! - Fortunately (sorry if I didnt mention it - all this equipment is already on the boat - i'm not buying it) the crank and the house batteries are very similar charge profiles - the house are a dual purpose battery and AGM - the crank are calcium, but according to Bosch the charge rates are compatible with the AGMS and can therefore be treated as AGM.

I did ponder over having the crank's vsr'd and the house on one of the engines - but that confused me on the wiring - and I think I would need to purchase a heap of decent cable to make this an option (not cheap in Aus) I also have the issue that if one engine goes down then i'm potentially not charging one or the other without some complex switching. As the batteries exist - using them is not an issue either way. I think this is where 2 VSRs and using both alternators comes in if its possible. I have recently had an incident where we came back on one engine due to a reef hit damaging the running gear - engine could run but didnt see the point when running back on a single engine for 3 hours.... so it does happen.

I'll have a look at these

I'm not spending a cent (well ok maybe a few dollars) - thats why i'm trying to maximise what I already have. I do not have the option for a single bank. The batteries are all under the rear deck each bank of 4 is in its own fibreglass box and sits on a shelf as far outside each side as they can do - the distribution of weight works port and starboard. with a lot of hassle I could run the batteries along the keel but it would make servicing the engines pretty miserable!

Not really an option a) finding that kind of thing in Aus would be hard and v expensive (not even sure if spring / hand starting a 6l diesel is even possible - plus I need power for the fuel solenoid etc) b) I already have the batteries and parts and its no issue with 250kg hanging at the back c) we may be on the hook for a week so like the option of completely isolated crank batteries just in case we run the house down too far.

As I mentioned - I already have everything it was already in place when I bough the boat - just configured very badly and wrongly - light and easy dont really matter in this instance. Correct and bullet proof do.

Well starters would have their own but would share with the house once charged. There are currently 3 alternators - very badly done and I dont want 3 alternators (or 4) - just 2. the 3rd is currently for house and is too small with a pathetic gauge wire to the house. The bracket it hangs on is badly made and doesnt look like it will last too long, or will chew through the belts. I like the simplicity of 1 alternator per engine! The charger is already there so can deal with 2 crank, 1 house - then the genset can have its own small charger to keep that topped up (or I could run off a crank battery but the weight saving is negligable)

Thanks for the info guys - Further discussion is welcome!

Steve

 

Of course non electrical starters are available in Australia. Can't say anything about price. As for power, spring starters are available for starting diesels up to 18l displacement. Most common ones are for 5-9l. As I said most people don't know they even exist. Here is a australian dealer if you wish to investigate. Air Starter | Turbine Starter | Austart | Hydraulic Starter | Spring Starter http://www.khequipment.com.au They carry all options, not only spring.

Now back to your problems. First issue is what batteries you have (or plan to fit). AGM and Calcium gel can have similar profiles or not. It depends on the brands used. In any case you need to know exactly at what voltages constant current and constant voltage charghing occures. Anyway your problem is charge acceptance. While the AGM can more or less take all the amps from the alternators during constant current charghing, the gels may not and you will fry them.

You want only 2 alternators. This means one heavy duty alternator on each engine. What is currently fitted to the engines and how are they regulated? You will want an external smart regulator capable of combining two alternators. Because you don't want an extra alternator for the starting batteries they must either be of the same type as the house, or you can charghe them with a dc-to-dc charger.
You may want to read some articles from this page Marine How To - DIY for Boaters https://marinehowto.com

 

Hi Rumars

Thanks for the info on the mechanical starters

The crank batteries are Calcium / Calcium Bosch 31-1000MF batteries - 1000CCA in a N31 case -sealed - they are similar to an AGM - details are scarce amazingly - but from what i have found initial charge rate is at 14.4v (bulk) - House batteries are E-NEX DC31MF - which again details are scarce but from what I can gather they are dual purpose batteries (crank with cyclic capability) 100ah batteries from the info I have they are AGM sealed - Bulk at 14.4 to 14.8v and float at 13.2 to 13.7v so match the Bosch ones pretty well.

The alternators on the cummins 6bta are standard again not 100% sure but are 105amp or 130amp (Boat is relatively new to me and i'm going through everything now) so plenty of grunt - but also potentially too much grunt. They are internally regulated - so can potentially link from the research i have done (although when close to full one alternator will drop off and leave the other to charge it.) It doesnt look like i Need a combiner unless i'm running unregulated output.

I'm trying to avoid DC-to DC chargers as they are very expensive here - and relatively low output the Stirling regulator would work better and seems to be cheaper (albeit I would need 2 of them) from what I have been reading I am now leaning toward the 2x VSR and combining both alternators to the house bank after cranks are up to voltage (another VSR is only $50). Tony at SBMAR shows a similar layout but using isolators rather than a VSR Typical DC Power Distribution Example - Seaboard Marine https://www.sbmar.com/articles/typical-dc-power-distribution-example/

Steve