Adding a 3rd battery or, a higher amp alternator? Which is best? Both isn’t the answer! CPAP

[Yeoman_24]

I currently have a 2 x 100 amp leisure batteries on my Moody 30 with 28hp Beta Marine engine and 65 amp alternator.
1 leisure battery is used for starting, 1 for ‘house’ and a 1 / both / 2 switch for starting, alternator charging, battery use, etc....... and that’s my set-up.
I’m thinking of adding a standard 65amp (roughly) starter battery and then have the 2 leisure batteries as house batteries.
Would forumites recommend this or, would I be better served by a 100 amp alternator instead?
The main reason I ask is I suffer from sleep aponea and have to use a travel CPAP machine which is a bit, ‘amp’ hungry. Manufacturers are gits to try and get me buy a 15v travel battery for .... £300 !!! I have their inverter which runs the machine from 12v through 15v inverter.
Hope this all makes sense but I can provide any links to CPAP data if required to help solve the problem!
Thanks

 

[pvb]

Add a starter battery and have the 2 x 100Ah batteries as your house bank. Absolutely no point in fitting a bigger alternator - batteries decide how much charge they can accept and your 65A alternator would be fine for, say, a 300Ah house bank, so you could even add another 100Ah battery to your house bank if you've space.

 

[jamie N]

Rather than upping your generating capacity, would it not be more cost effective to decrease your consumption?
Do you have LED's throughout, for example, and so on?


Apologies! Have just reread, and seen your special requirements. More capacity is the better option I reckon, as suggested by PVB.

 

[Yeoman_24]

Add a starter battery and have the 2 x 100Ah batteries as your house bank. Absolutely no point in fitting a bigger alternator - batteries decide how much charge they can accept and your 65A alternator would be fine for, say, a 300Ah house bank, so you could even add another 100Ah battery to your house bank if you've space.

That was my original thought so good to have it as your suggestion. I don’t suppose you could suggest a wiring diagram anywhere?

 

[Yeoman_24]

Rather than upping your generating capacity, would it not be more cost effective to decrease your consumption?
Do you have LED's throughout, for example, and so on?


Apologies! Have just reread, and seen your special requirements. More capacity is the better option I reckon, as suggested by PVB.

Thanks, got led’s and currently (no pun intended) do all I can to minimise consumption to support CPAP use

 

[halcyon]

I currently have a 2 x 100 amp leisure batteries on my Moody 30 with 28hp Beta Marine engine and 65 amp alternator.
1 leisure battery is used for starting, 1 for ‘house’ and a 1 / both / 2 switch for starting, alternator charging, battery use, etc....... and that’s my set-up.
I’m thinking of adding a standard 65amp (roughly) starter battery and then have the 2 leisure batteries as house batteries.
Would forumites recommend this or, would I be better served by a 100 amp alternator instead?
The main reason I ask is I suffer from sleep aponea and have to use a travel CPAP machine which is a bit, ‘amp’ hungry. Manufacturers are gits to try and get me buy a 15v travel battery for .... £300 !!! I have their inverter which runs the machine from 12v through 15v inverter.
Hope this all makes sense but I can provide any links to CPAP data if required to help solve the problem!
Thanks

Never looked before, mine is 24 volt 3.5 amp, be tempted to just fit another 100 amp hour battery in parallel and carry on as before.

Brian

 

[pvb]

That was my original thought so good to have it as your suggestion. I don’t suppose you could suggest a wiring diagram anywhere?

Just wire the house batteries in parallel.

 

[RichardS]

Add a starter battery and have the 2 x 100Ah batteries as your house bank. Absolutely no point in fitting a bigger alternator - batteries decide how much charge they can accept and your 65A alternator would be fine for, say, a 300Ah house bank, so you could even add another 100Ah battery to your house bank if you've space.

That is the best solution.

Richard

 

[Daverw]

I also use a cpap and is 240v and use via little 300w inverter, I did have one supplied originally that had 12v or mains, My current one is mains with a power adapter that supplys 24v at 3.75amps but when on the boat via the invertor reads less than 0.5 amp, we have 3 x 110ah house and all lamps etc are LED and find the cpap does not use as much as expected, we try not to run the fridge over night.

 

[Gwylan]

Get a diode to split the charge and have 1 battery for domestic, 1 for the CPAP machine and a starter battery on separate circuits.
Then have a dedicated socket for the CPAP.
For the CPAP include a limiter that will stop it running the battery too low.

Have individual on-off switches for each of the circuits.
Cheap Aldi-Lidl smartish charger for each one for when you are connected to the mains

We have a similar setup with the 2 domestic batteries in parallel and dedicated fridge and starter batteries. Look for the different ways of paralleling batteries if you go that route.
When all else fails there is a modified jump lead to start the engine from the domestic if thing go T.U.

 

[PaulRainbow]

That was my original thought so good to have it as your suggestion. I don’t suppose you could suggest a wiring diagram anywhere?

Post #2 is correct, IMO.

It's a simple job to wire the additional battery in parallel. If you added a VSR you wouldn't have to fiddle around with the 1-2-B switch to keep the batteries all charged. They would all get charged whether the switch was on 1 or 2 (don't use it on both).

Here's a basic schematic, if you don't want to fit the VSR simply leave it out.

 

[PaulRainbow]

Get a diode to split the charge and have 1 battery for domestic, 1 for the CPAP machine and a starter battery on separate circuits.

and lose about 0.7v from the alternator charging ?

Then have a dedicated socket for the CPAP.
For the CPAP include a limiter that will stop it running the battery too low.

Hmmm... so the CPAP gets cut off from the battery to prevent it going flat and the OP dies in his sleep, even though the other battery might have been fully charged ?

Might be better to parallel the two batteries and have double the power available. Wouldn't hut to have a low voltage alarm.

Have individual on-off switches for each of the circuits.
Cheap Aldi-Lidl smartish charger for each one for when you are connected to the mains

We have a similar setup with the 2 domestic batteries in parallel and dedicated fridge and starter batteries. Look for the different ways of paralleling batteries if you go that route.
When all else fails there is a modified jump lead to start the engine from the domestic if thing go T.U.

Might be passable for the fridge, no-one dies if the fridge defrosts.

But, why not just connect the three batteries in parallel ? They'd have to be very small or very knackered if they couldn't run the fridge overnight. I have 3 domestic batteries and my fridge is always on. I'm running on solar power 24/7 at the moment and the batteries don't get below about 12.5v overnight.

 

[William_H]

The simplest easiest unders tood is to wire the both 100AH leisure batteries in parallel. Then wire the new starter (large CCA) battery in place of the leisure battery disconnected. That will leave you with a system operated as before but you need to make sure you use the correct battery selection to the starter battery for start "both" for charging from engine then the selection to the double leisure battery set up for over night use. Then if you want you wire as shown a VSR between batteries so you can charge both battery banks automatically when you start the engine. Still need to start on the correct start battery position and move to domestic 2x100 for over night.
Then you may wish to move the CPAP and other domestic loads directly to the 2X100 batteries via a isolator switch. Then finally you remove 1,2,both switch and fit a simple isolation switch for the engine electrics. Lots of diagrams etc but important you understand what and why you are doing. ol'will

 

[PaulRainbow]

The simplest easiest unders tood is to wire the both 100AH leisure batteries in parallel. Then wire the new starter (large CCA) battery in place of the leisure battery disconnected. That will leave you with a system operated as before but you need to make sure you use the correct battery selection to the starter battery for start "both" for charging from engine

Sorry Will, i have to disagree here. The "both" setting should only be used for emergencies, using it for routine charging leaves the operator vulnerable to flat batteries in certain failure cases, or if he should forget to switch it back later.

then the selection to the double leisure battery set up for over night use. Then if you want you wire as shown a VSR between batteries so you can charge both battery banks automatically when you start the engine. Still need to start on the correct start battery position and move to domestic 2x100 for over night.

The other school of thought is to just use the bigger bank for everything, including engine starting, and keep the smaller battery as an emergency for engine starting. Nothing wrong with either method.

Then you may wish to move the CPAP and other domestic loads directly to the 2X100 batteries via a isolator switch. Then finally you remove 1,2,both switch and fit a simple isolation switch for the engine electrics. Lots of diagrams etc but important you understand what and why you are doing. ol'will

This would be the best way of doing it, with some form of split charging and a 3rd switch for emergencies. Here's a basic schematic for anyone interested.

 

[Rappey]

Putting larger alternators on an engine may not be a good move according to something I read.
There is a company that specialise in bmc.( 1.5 litre, 38-40hp )
75 amp is the largest they recommend as any larger puts way more strain on the pulleys and bearings than was ever intended.
Can't say this applies to all makes but sounds feasible?

 

[prv]

Hmmm... so the CPAP gets cut off from the battery to prevent it going flat and the OP dies in his sleep

A CPAP machine isn't life-support - if it were to stop running he would most likely just start snoring loudly and then wake up in the morning feeling tired and busting for a pee.

I am rather surprised that his machine is so power-hungry that it needs modifications to the boat's power supply, though. A look at the rating plate (of machine and 12v adapter) would be helpful.

Pete

 

[pvb]

Putting larger alternators on an engine may not be a good move according to something I read.
There is a company that specialise in bmc.( 1.5 litre, 38-40hp )
75 amp is the largest they recommend as any larger puts way more strain on the pulleys and bearings than was ever intended.
Can't say this applies to all makes but sounds feasible?

With a single V-belt, a 90A alternator (for 12v system) is about the biggest which won't cause undue belt wear. The flat multi-V belts fitted to modern engines can take bigger alternator loads.

 

[RupertW]

Sorry Will, i have to disagree here. The "both" setting should only be used for emergencies, using it for routine charging leaves the operator vulnerable to flat batteries in certain failure cases, or if he should forget to switch it back later.



The other school of thought is to just use the bigger bank for everything, including engine starting, and keep the smaller battery as an emergency for engine starting. Nothing wrong with either method.



This would be the best way of doing it, with some form of split charging and a 3rd switch for emergencies. Here's a basic schematic for anyone interested.

Disagree on the Both setting. If Both was for emergencies only then a VSR would be pointless as its entire function is to toggle between 1 and Both.
A VSR just does automatically what a 1-2-B does manually when used well.
The merits of automatic versus manual is a whole other topic.

 

[lw395]

I currently have a 2 x 100 amp leisure batteries on my Moody 30 with 28hp Beta Marine engine and 65 amp alternator.
1 leisure battery is used for starting, 1 for ‘house’ and a 1 / both / 2 switch for starting, alternator charging, battery use, etc....... and that’s my set-up.
I’m thinking of adding a standard 65amp (roughly) starter battery and then have the 2 leisure batteries as house batteries.
Would forumites recommend this or, would I be better served by a 100 amp alternator instead?
The main reason I ask is I suffer from sleep aponea and have to use a travel CPAP machine which is a bit, ‘amp’ hungry. Manufacturers are gits to try and get me buy a 15v travel battery for .... £300 !!! I have their inverter which runs the machine from 12v through 15v inverter.
Hope this all makes sense but I can provide any links to CPAP data if required to help solve the problem!
Thanks

You need to take a step back and re-examine the problem.
How many Ah per 24 hours do you need? Until you know that, you are just laying your self open to people shoving their favourite solutions and opinions on generalsied boat electrics at you.
When you know what you need in Ah, then you can look at how best to service that.
Do you run the engine for several hours every day? Or does your battery capacity need to provide for your needs for a long weekend?
If you want to do say a fortnight's cruise, how do you expect your pattern of engine use to look? How much access to shore power do you expect? How many nights in harbour vs on passage?

If your real problem turns out to be that on a normal sailing day you don't run the engine enough to recharge, adding battery capacity may not help.
A more modern alternator which charges at a higher voltage might help.
Some solar panels which mean you start every weekend from fully charged batteries might help.
But you need to consider your pattern of use of the boat to make a proper decision.

A portable battery you can take ashore and get charged might be a solution worth looking at? Lithium battery pack of some sort?
If this machine matters, then you maybe should have an independent supply for it and not have it fail because you've use too much cabin light or something.

 

[Tammany]

Sorry Will, i have to disagree here. The "both" setting should only be used for emergencies, using it for routine charging leaves the operator vulnerable to flat batteries in certain failure cases, or if he should forget to switch it back later.



The other school of thought is to just use the bigger bank for everything, including engine starting, and keep the smaller battery as an emergency for engine starting. Nothing wrong with either method.



This would be the best way of doing it, with some form of split charging and a 3rd switch for emergencies. Here's a basic schematic for anyone interested.

Mine is more or less exactly like this but with an added mains & solar controller connected to the domestic bank that will also charge the starter battery via a dual VSR. Never had any issues with it at all including over winter sailing when the solar doesn't do much. Rarely plug into mains but occasianally run engine.