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Doing without a dedicated starter battery?


Awayonmyboat

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Hi all,

 

I have a 57 footer with an Isuzu diesel fitted with twin 80 Amp alternators, 3 X 110 Amp hour domestic batteries plus one starter battery. I estimate use about 100 Amp hours per day for lighting, fridge, charging phones etc. The boat will be used for cruising (no regular hook up) 8- 9 months of the year but spend winter in the marina.

 

I am planning to redo the current ramshackle battery and alternator wiring plus get new batteries (Carbon foam AGM for the domestic chosen for their good partial charge performance and cycle life at a reasonable price - I'm not ready to invest in Lithium) .

 

My original plan was to connect the two alternators both to the domestic batteries and then charge the start battery via a voltage sensitive relay. Basically I would be following advice I have found elsewhere on this forum to ensure I got best charging performance.

 

A variation to this has now occurred to me. That is to simply fit 4 identical 110 Amp hour batteries (charged by the two alternators plus solar when the sun is out) and delete the separate starter battery. So everything will now be run from these four including the starter. My logic is that since starter consumption is minimal (typically only 1-2 Ahr per day) doing it this way maximises my domestic bank size and so with normal daily it use will be slightly less discharged. I believe this means I can go extra day without recharging or alternatively I will get slightly better life out of my batteries.

 

I understand of course this will give me no backup start capability should I inadvertently run my batteries too low. Realistically though I think there is is a low risk of happening (I have decent battery monitoring planned to go in at the same time) and given we are talking a canal boat the consequences should I do it, are also low. I'm also thinking I could buy a car type jump start pack as a backup if I find myself worrying about this to much. 

 

And in case you are wondering why I do not simply fit 4+1 batteries, it is because I do not have the space easily available - a fair bit of rebuilding would need to be done to achieve it.

 

I'm always cautious about reinventing the wheel so has anyone else gone this way or is there something else I've missed which means it is not a good idea?

 

Thanks in advance for your thoughts.

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Daft idea just to save the cost of a VSR. The day you have an engine problem necessitating much cranking you will regret this system.

Why try to be different?

Why do you think everyone else has a seperate battery? Because its sensible.

Just have a small 80Ah start battery charged by a VSR and you have no worries,

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9 minutes ago, Tracy D'arth said:

Daft idea just to save the cost of a VSR. The day you have an engine problem necessitating much cranking you will regret this system.

Why try to be different?

Why do you think everyone else has a seperate battery? Because its sensible.

Just have a small 80Ah start battery charged by a VSR and you have no worries,

A starter battery is another form of insurance, I doubt your boat will catch fire or sink during the next 12 months, so why buy insurance?  Because if/when disaster happens you will realise why everyone else does.............

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Juno has one battery, she also has an outboard that you can hand start if need be....

 

In my yoof hire boats often had only one battery, or at least only one battery bank, they also had engines you could hand start...

 

On Lutine Bell I found the benefits of split charge worked both ways - when the starter battery was knackered, which happened, the domestics could be pressed into service to start the engine. I also found that with four  identical batteries it was worth swapping them round every couple of months, which prolonged the battery life somewhat. I did tell the guy who bought her she needed new batteries, but also she needed new everything by then. 

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Loddon only has space for 4 batteries and is set up as follows

3 batteries charged by 90amp alternator.

VSR feeding :

Starter battery charged by 60amp alternator.

 

it works

 

Advantages 

Any charging source (solar or mains battery charger) charges all batteries.

After a short period both alternators charge all batteries (alternator voltages need to be matched for optimum performance)

If I flatten domestics I can still start the engine.

 

Disadvantages 

I lose about 40Ah capacity compared to having 4 batteries on the domestics.

 

Its not worth trying to re invent the wheel unless you have an engine you can handstart.

 

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1 hour ago, Awayonmyboat said:

I'm also thinking I could buy a car type jump start pack as a backup if I find myself worrying about this to much. 

 

That is just an extra battery. And it needs to be kept charged to ensure it is going to be useful when (not if) the need arises. Easier just to fit a conventional start battery.

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I have 2 banks and a two way switch . So neither is dedicated either can be domestic or start.

However I ‘designate’ bank one as start, and part of my switch off routine is to turn from 1 plus 2  to 2 at the end of the day.
 

However the rotary switch is right next to the Charging circuit exciting switch, and there are 2 warning  lights, one in the engine room and one by the stern doors. Thats a visual cue to put everything to bed.

The only boat i had with any form of split charge system, let me down when it failed, forcing  its removal.
 

If you are the sort who shuts the engine down on a key and wanders off you probably need a failsafe, if you have a shut down routine,(turn off engine , sort electrics, dip tanks, grease sterngear, remove exhaust stack, shut pigeon box wipe down engine ,  ) you are probably safer.

 

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1 hour ago, Awayonmyboat said:

 


. I'm also thinking I could buy a car type jump start pack as a backup if I find myself worrying about this to much. 

 

You will not start a diesel with one of those reliably, besides it will need charging when you discover you need it!

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2 hours ago, Awayonmyboat said:

Hi all,

 

I have a 57 footer with an Isuzu diesel fitted with twin 80 Amp alternators, 3 X 110 Amp hour domestic batteries plus one starter battery. I estimate use about 100 Amp hours per day for lighting, fridge, charging phones etc. The boat will be used for cruising (no regular hook up) 8- 9 months of the year but spend winter in the marina.

 

I am planning to redo the current ramshackle battery and alternator wiring plus get new batteries (Carbon foam AGM for the domestic chosen for their good partial charge performance and cycle life at a reasonable price - I'm not ready to invest in Lithium) .

 

My original plan was to connect the two alternators both to the domestic batteries and then charge the start battery via a voltage sensitive relay. Basically I would be following advice I have found elsewhere on this forum to ensure I got best charging performance.

 

A variation to this has now occurred to me. That is to simply fit 4 identical 110 Amp hour batteries (charged by the two alternators plus solar when the sun is out) and delete the separate starter battery. So everything will now be run from these four including the starter. My logic is that since starter consumption is minimal (typically only 1-2 Ahr per day) doing it this way maximises my domestic bank size and so with normal daily it use will be slightly less discharged. I believe this means I can go extra day without recharging or alternatively I will get slightly better life out of my batteries.

 

I understand of course this will give me no backup start capability should I inadvertently run my batteries too low. Realistically though I think there is is a low risk of happening (I have decent battery monitoring planned to go in at the same time) and given we are talking a canal boat the consequences should I do it, are also low. I'm also thinking I could buy a car type jump start pack as a backup if I find myself worrying about this to much. 

 

And in case you are wondering why I do not simply fit 4+1 batteries, it is because I do not have the space easily available - a fair bit of rebuilding would need to be done to achieve it.

 

I'm always cautious about reinventing the wheel so has anyone else gone this way or is there something else I've missed which means it is not a good idea?

 

Thanks in advance for your thoughts.

I think you have identified the main problem which is the risk of not being able to start the engine. As you imply, this is a pretty low risk and not catastrophic if it were to come to pass. Having a set of jump leads would be a good idea.

 

i suppose the only other issue is that when you operate the starter the system voltage to the domestic circuits will dip quite a bit, and when you release the starter switch there will be a bit of a voltage spike, but whether or not this would be an issue I suppose depends on what you have connected and switched on at the time. Most likely it would be a non-issue.

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22 minutes ago, Loddon said:

Loddon only has space for 4 batteries and is set up as follows

3 batteries charged by 90amp alternator.

VSR feeding :

Starter battery charged by 60amp alternator.

 

it works

 

Advantages 

Any charging source (solar or mains battery charger) charges all batteries.

After a short period both alternators charge all batteries (alternator voltages need to be matched for optimum performance)

If I flatten domestics I can still start the engine.

 

Disadvantages 

I lose about 40Ah capacity compared to having 4 batteries on the domestics.

 

Its not worth trying to re invent the wheel unless you have an engine you can handstart.

 

 

For clarity I think the VSR would have to be bi-directional if it was to allow charging the domestic bank in the event of domestic charge source failure.

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10 minutes ago, Tony Brooks said:

 

For clarity I think the VSR would have to be bi-directional if it was to allow charging the domestic bank in the event of domestic charge source failure.

Not if you wire it as mine is with the sense side on the domestics. I realise this slightly delays the connection until the domestics get to 13.2v but in practice on my setup that is only a few minutes.

That is also the reason I said I only lose about 40Ah capacity rather than 55Ah from the extra 110Ah starter battery as I doesn't disconnect until both banks have dropped to 12.6v

Edited by Loddon
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1 minute ago, Loddon said:

Not if you wire it as mine is with the sense side on the domestics. I realise this slightly delays the connection until the domestics get to 13.2v but in practice on my setup that is only a few minutes.

So in the even of the domestic  charge source failing how does the VSR see the 14V on the engine battery rather than the 12.5V ish on the domestics? I agree with solar as well as engine charging its less likely but by simply fitting a bi-directional VSR that is eliminated

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3 minutes ago, Tony Brooks said:

So in the even of the domestic  charge source failing how does the VSR see the 14V on the engine battery rather than the 12.5V ish on the domestics? I agree with solar as well as engine charging its less likely but by simply fitting a bi-directional VSR that is eliminated

In that extremely unlikely event:

A jump lead from the starter battery ;)

 

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Comments abobe have ignored the fact that 'paralelling two alternators' won't work - well, mebe won't be effective as the more powerful one will take over  (for several reasons) - thus there's no advantage.

Applying the KISS principle, leave thing as they are, the smaller 'house' alternator charges the SEPARATE engine / starter battery and the big alternator looks after the domestic set.

I've just bought an inexpensive 80 amphour 096 starter battery from BMS (work it out) for fifty six quid just as a spare for the boat (the existing is possibly dead as it hasn't been charged since March). If it's OK I can use the 096 as a spare for our cars for when their's dies...

 

I'm sure there must be some space in the engine bay for the starter battery - it doesn't have to be near the domestics - and keep these as a 4 pack because your usage calculations are bound to be wrong / changing - which will kill the smaller set in pretty short order.  

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2 minutes ago, OldGoat said:

Comments abobe have ignored the fact that 'paralelling two alternators' won't work - well, mebe won't be effective as the more powerful one will take over  (for several reasons) - thus there's no advantage.

 

This is simply not true. You are just repeating something you heard down the pub, therefore, very unhelpful.

Edited by nicknorman
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1 minute ago, nicknorman said:

This is simply not true. Therefore, very unhelpful.

Perhaps you could explain, pretty please?

 

(I'm taking "paralelling" as just that connecting the two outputs directly to the batteries without any smoking mirrors in between)

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Just now, OldGoat said:

Perhaps you could explain, pretty please?

 

(I'm taking "paralelling" as just that connecting the two outputs directly to the batteries without any smoking mirrors in between)

If you connect two alternators to a large battery needing to be charged, probably at first both alternators will be unable to supply enough current to get the terminal voltage up near their regulated value. ie what we normally call “bulk phase”. They will both therefore be producing maximum output.

At some later point the maximum current the batteries will take when charged near the regulated voltage, will become less than maximum output and so the combined charge current will decrease. Whether or not the alternators reduce their outputs by the same proportion depends on their regulators (regulated voltage, loop gain etc), not on the size of the alternators.

 

If there is a significant mismatch between the alternators’ regulators then it may well be that one alternator reduces its output more than the other, and it is possible that eventually one alternator will be producing zero current whilst the other is still producing significant current, but this doesn’t really matter because the batteries are still taking whatever current they can manage.
 

People imagine that alternator regulators are near perfect, ie if it is a 14.4v regulator on a 100A alternator, that it is capable of producing 100A at up to just under 14.4v. Whereas in fact the soft regulation (low loop gain) means that the load (batteries) need to pull the system voltage down to well below 14v in order to get 100A out of the alternator. If the batteries hold the system voltage down to say 14.1v, then probably the alternator will only produce ~40A (guessing). There is in reality a very gradual progression between “bulk” and “absorb”, it is not a binary thing.

So to summarise the advantages of paralleling 2 alternators:

 

1/ higher (maybe double) maximum output which shortens bulk charge time and allows a heavy load such as an inverter running a washing machine heater without taking anything much from the batteries.
 

2/ shortened absorb time due to the higher current available as the system voltage approaches the regulated voltage.

 

3/ during much of the charge period ie once the charge current starts to reduce, or when powering a heavy load, the alternators are working less hard, therefore run cooler therefore last longer.
 

Disadvantages:

 

1/ Need for spilt charge mechanism.

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As an aside, with my home made digital alternator regulator that has very high loop gain and thus will produce maximum output to within about 0.1v of regulated voltage, it is amazing how quickly the batteries now charge.

 

So having previously been a bit sceptical about Adverc or Sterling alternator controllers, I now see the point. All because built in analogue regulators in alternators are so crap!

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I had those lovely Adverc people design and supply a circuit and controller for my 500AH 24V charging regime (blocking diodes, separate feeds to the alternator controllers etc). Result - no  practical difference in charge current whether alternator No:1 or No:2 or both used. I was a tad disappointed.

 

My initial comment of 'won't work' was for the assembled audience who might be tempted to bang in a couple of alternators and expect an instant increase in charging. There's a lot more to it - hence the warning note.

I will no go and  sulk.

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47 minutes ago, OldGoat said:

I had those lovely Adverc people design and supply a circuit and controller for my 500AH 24V charging regime (blocking diodes, separate feeds to the alternator controllers etc). Result - no  practical difference in charge current whether alternator No:1 or No:2 or both used. I was a tad disappointed.

 

My initial comment of 'won't work' was for the assembled audience who might be tempted to bang in a couple of alternators and expect an instant increase in charging. There's a lot more to it - hence the warning note.

I will no go and  sulk.

Maybe Adverc weren’t as clever as you’d hoped?
 

I don’t know if I explained it adequately earlier, but the regulator behaviour is an important point. As the battery voltage rises, the current produced by the alternator decreases over quite a wide range of voltage. We hear of people with 70A alternators who say they only get 70A for a few minutes, it is then 60A, 50A and for most of the time, 30A or less. This is because of the regulator behaviour and also possibly due to voltage drop on the wiring.

 

But anyway, the point is that at a battery voltage of say 13.9v, the current will be x% of the maximum output, let’s say 50%. 50% of 70A is 35A. But if you have two 70A alternators then you get 50% of 70A x 2 ie 70A.
If you have a 175A alternator you get 50% of that which is 87.5A, which is why even with our old regulator we would be getting over 70A for several hours.

 

Of course when you double the alternator capacity you don’t halve the charge time because ramming more current in, increases battery voltage which reduces alternator output. The gains you get depend on the relationship between the alternator max output, battery capacity and starting SoC. Our 175A alternator into 450Ah with standard regulator is only in “bulk” for a few seconds, after 5 mins the current is down to 120A or so. So if we added a second 175A alternator it would make minimal difference. Whereas if we had a 30A alternator, adding another one would make a big difference.

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1 hour ago, nicknorman said:

As an aside, with my home made digital alternator regulator that has very high loop gain and thus will produce maximum output to within about 0.1v of regulated voltage, it is amazing how quickly the batteries now charge.

 

So having previously been a bit sceptical about Adverc or Sterling alternator controllers, I now see the point. All because built in analogue regulators in alternators are so crap!

Ive been saying this for years, I would be lost without the Adverc. Tight voltage regulation gives a full bulk charge right up to absorption whilst vague voltage regulators have a huge grey area of bulk-absorption inbetween-ness

 

As for joining alternators, during bulk charge I am charging from the 100amp domestic alternator, the 70 amp starter alternator, a 30 amp Victron charger from the Travelpower, and a bit from solar. They all sort of work together though I did have to change the Victron voltage settings (using my phone, all high tech stuff) to make it work. I try to remember to "un join" the alternators once we get past bulk else a bit of confusion sets in, not helped by the Advercs voltage cycling.

 

.................Dave

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6 hours ago, nicknorman said:

As an aside, with my home made digital alternator regulator that has very high loop gain and thus will produce maximum output to within about 0.1v of regulated voltage, it is amazing how quickly the batteries now charge.

 

So having previously been a bit sceptical about Adverc or Sterling alternator controllers, I now see the point. All because built in analogue regulators in alternators are so crap!

We had a Balmar regulator and the new lead carbon batteries which have better acceptance than standard lead acid and the charging time was much more rapid. You could see a sharp delineation between bulk and absorption, bulk was truly constant current right up to the point 14.2V was reached, giving faster charging. The absorption phase was not some protracted period where the alternator was being backed off as the voltage slowly crept up, soft regulation really does extend the absorption phase. 

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9 hours ago, Tracy D'arth said:

Daft idea just to save the cost of a VSR. The day you have an engine problem necessitating much cranking you will regret this system.

Why try to be different?

Why do you think everyone else has a seperate battery? Because its sensible.

Just have a small 80Ah start battery charged by a VSR and you have no worries,

 

Another advantage of a smaller, separate cranking battery is that when it goes flat (eg lack of use during lockdown) you can more easily take it out to use a domestic (car) battery charger. Don't ask me why I think this is a good idea, but when the battery gets a bit knackered (and it will do, sooner or later) it saves a lot of mither. 

 

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