Improving battery charging

[KenK]

Hi All,

I know that the subject of battery charging is dear to all our hearts and has been discussed at length but this is a specific rather than a general question so hopefully it won't start a fight.

 

I’d like to improve the battery charging system on my boat so I’m looking for suggestions. The current setup is as follows:-

 

Beta 38 engine.

 

40 Amp battery sensed alternator charging 110 Amp engine start battery.

70 Amp machine sensed alternator converted by an external Beta alternator controller to battery sensing charging six 110 Amp leisure batteries.

Sterling 3000W pure sine wave inverter.

 

The problem is that the leisure batteries take quite some time to become fully charged. The alternator is working correctly, as is the controller but it is a lot of batteries and a fairly small alternator.

 

The options are, connect the two alternators together using one of the many systems available or replace the 70 Amp with a larger alternator. I feel the first option makes the most sense but what’s the best system to use and why?

 

 

 

Ken

[John Orentas]

Hi Ken.

 

On the face of it, what you have is close to the best you can do. There is or was at one time a convention that said that a ten hour charge rate is a reasonable maximum charge rate, i.e. your 660 amp/hours = 10 hour charge at 66 amps.

 

Of course these figures have always been known to be very theoretical and very approximate, but we must accept that there is a finite limit to how fast a battery can be charged without paying a heavy cost in terms of the life of batteries and other equipment.

[matrix]

Hi All,

I know that the subject of battery charging is dear to all our hearts and has been discussed at length but this is a specific rather than a general question so hopefully it won't start a fight.

 

I’d like to improve the battery charging system on my boat so I’m looking for suggestions. The current setup is as follows:-

 

Beta 38 engine.

 

40 Amp battery sensed alternator charging 110 Amp engine start battery.

70 Amp machine sensed alternator converted by an external Beta alternator controller to battery sensing charging six 110 Amp leisure batteries.

Sterling 3000W pure sine wave inverter.

 

The problem is that the leisure batteries take quite some time to become fully charged. The alternator is working correctly, as is the controller but it is a lot of batteries and a fairly small alternator.

 

The options are, connect the two alternators together using one of the many systems available or replace the 70 Amp with a larger alternator. I feel the first option makes the most sense but what’s the best system to use and why?

 

Ken

 

 

hi ken

take a look at sterlings website here http://www.sterling-power.com/products-altbatt.htm

they have a battery charger system that uses both your alternators to charge your domestic batteries

it sounds good in theory anyway

[KenK]

Thanks for the input so far. I have looked at the various websites, Smartgauge, Sterling, Adverc etc. naturally they all claim their system is best. What I'm looking for is real world information, what do you have and does it work?

 

Thanks

 

Ken

[frangar]

I have an Adverc fitted for 10+ years with no problems, All Adverc's I have fitted on other boats have also worked from day one with no trouble.....however I have heard that the Beta unit can get unreliable. Having said that beware of units which promise to recharge your 800ah battery bank in 10 min.....your batteries WILL protest esp. if traction cells/gel/sealed whatever anyone says!! Cue diatribe from a few well known parties.......

 

Gareth

[John Orentas]

Thanks for the input so far. I have looked at the various websites, Smartgauge, Sterling, Adverc etc. naturally they all claim their system is best. What I'm looking for is real world information, what do you have and does it work?

 

Thanks

 

Ken

 

 

Hi Ken.

 

Yes these devices seem to do the job if you are desperate for the last amp of power. In my view though you should avoid like the plague any any contraption that connects together two alternators, there have been on or two threads about the things in the past.

[chris w]

There is no problem in connecting 2 alternators together from a power point of view and you will get the combined current. The outputs of both alternators are connected to the outside world through internal diodes so are isolated from one another. You will not blow up an alternator by doing this.

 

The only slightly negative phenomenon that may occur is that your tacho may not always operate correctly. Without going deeply into the reason, it is basically due to differences in the absolute output voltage of the two alternators at different revs.

 

I happen to have a Sterling Alternator Controller and, once the battery voltage exceeds the regulator voltage (14.2v in my case), the controller allows a very healthy increase in current (a factor of x2 for most of the cycle) as it allows the battery voltage to increase to 14.8v (for wet lead acid batteries). The Sterling also has battery AND alternator temperature monitoring (with auto cut-out in the event of an over-temperature alarm) and the option of a remote display which I have and find very useful.

 

Chris

Edited August 28, 2007 by chris w

[Sir Nibble]

Slap a split charge relay in to connect both alternator connections together. There is no problem with connecting alternators in this way and no prospect of causing damage to either. Run the relay from whichever alternator cuts in at the highest speed.

[John Orentas]

Slap a split charge relay in to connect both alternator connections together.

 

 

Brilliant ! What you are really saying Snibble is 'As long as nothing goes wrong you won't have problems'.

 

The point is that you are destroying the whole elegant concept of using two separate alternators at the centres of two entirely independent electrical circuits.

 

Designers always strive to gain this kind of double safeguard built into any kind of system or machinery, that's why we don't have too many single engine airliners.

[bottle]

SNIP>>>>>>>>>>>>>>>>>>

 

the whole elegant concept of using two separate alternators at the centres of two entirely independent electrical circuits.

 

<<<<<<<<<<<<<<<<<<SNIP

 

I agree with this whole heartedly.

 

Keep them separate.

[chris w]

As usual John, that's total b*ll*cks.

 

Firstly where does Snibble say, "As long as nothing goes wrong you won't have problems"? He categorically states (and I for one agree with him). "There is no problem with connecting alternators in this way and no prospect of causing damage to either".

 

There are not, generally, redundant systems on narrowboats as you seem to imagine. The fact that one alternator may be charging the starter battery and one alternator the domestic batteries does not make those redundant systems. They are simply two independent single-point-of failure systems. If an alternator fails, the respective charging system is kaput.

 

If, however, we connect them together (remember they are isolated from each other due to their output stages) we do create a redundant system and of which I'm surprised your 60 years in electronics and your similar numbered IQ didn't avail you.

 

So if, say, an alternator belt broke the other alternator will still supply the batteries. So we are no worse off and most likely better off - we have created a redundant system and maximised the available current.

 

Chris

Edited August 28, 2007 by chris w

[ChrisPy]

IF ...................

 

if things really get that dire it's easy enough to bridge between the engine battery and the domestic bank with a jumper lead until you can fix the problem.

 

I agree with John that there is little to be gained by linking the systems.

[carlt]

but this is a specific rather than a general question so hopefully it won't start a fight.

[Sir Nibble]

I agree with John that there is little to be gained by linking the systems.

I actually did this last week, the "little to be gained was 35A of extra charge at a fast idle.

[ChrisPy]

dammit, I can't find my coat .....

[Welk]

I think there's a few issues to address.

If you are going to effectively connect the Leisure Batteries directly to the Engine (starter) batteries, then it might be a good idea to ensure that the battery banks use the same type of Batteries, also be aware that if the battery banks discharge then the engine will not start with the starter motor.

If you are going to relay connect them when the engine is running then be aware that any Potential Difference between the battery banks may result in a very high instantaneous current when the relay is energized, although the voltage drop when the starter motor is activated may suppress the problem, and hopefully the alternators will kick in before any noticeable damage is done.

If you are going to use a diode bridge then the voltage drop across the diodes will effectively mean that the charging voltage is dropped, and so your charge will reduce.

[gralyn]

I seem to recall that the length of cable to the battery is an influence on how well the bank charges. The length should be the same even if it means an intermediate connecting point. This is difficult to describe in print but if your battery bank is parallell connected by all the +ve terminals and all the -ve terminals connected with one battery at the end of the line then that battery will not receive a full charge untill all the others have been charged and so on up the line. Using the same length of cable to all +ve terminals and -ve terminals connected to a single cable coming from the alternator charging +ve and -ve scource will ensure that all batteries in the bank are charged to the same level.

[chris w]

I think there's a few issues to address.

 

..............If you are going to use a diode bridge then the voltage drop across the diodes will effectively mean that the charging voltage is dropped, and so your charge will reduce.

 

Not strictly true. You will only reduce charging current if your alternators are machine sensing rather than battery sensing. If you use an alternator controller you will have battery sensing.

 

Chris

[ChrisPy]

I seem to recall that the length of cable to the battery is an influence on how well the bank charges. The length should be the same even if it means an intermediate connecting point. This is difficult to describe in print but if your battery bank is parallell connected by all the +ve terminals and all the -ve terminals connected with one battery at the end of the line then that battery will not receive a full charge untill all the others have been charged and so on up the line. Using the same length of cable to all +ve terminals and -ve terminals connected to a single cable coming from the alternator charging +ve and -ve scource will ensure that all batteries in the bank are charged to the same level.

or more easily, link the +ve terminals from left to right, and take the feed and alternator connection from the +ve of the right hand battery. do the opposite with the -ve connections. Then the total length of cable to/from each battery should be more or less the same.

[Sir Nibble]

Lordy! I had no idea this was so complicated.

Connect alternator out put to alternator output through a decent relay run from which ever alternator cuts in last. There will be no current transfer between the batteries unless you apply a BIG load whilst the motor is running. Everything else is looking for problems that aren't there.

[KenK]

IF ................... if things really get that dire it's easy enough to bridge between the engine battery and the domestic bank with a jumper lead until you can fix the problem.I agree with John that there is little to be gained by linking the systems.

Hi Chris, What we found on our last outing to Bristol from Newbury and back is that if we had a nice clear section 15 mile pound for example we had plenty of power in the batteries. On the other hand Caen Hill locks and very little charge in the batteries. Now that makes sense we have a240V fridge powered by the inverter, so on the lock sections we probably have more going out than comming in. But we also have a 40 amp alternator basicly doing nothing for most of the time its spinning anyway so we might as well use the power.Ken

Hi Carl,Yeh I know I should have known better. Ken

[Sir Nibble]

I,m a bit worried that folk will begin to think I have a bee in my bonnet about this, but here goes.

15 mile pound for example we had plenty of power in the batteries. On the other hand Caen Hill locks and very little charge in the batteries.

Your alternator is revving too slow.

[chris w]

I agree with Snibble. Idling with low batteries, you should typically be getting more than 1/3 of your alternator's nominal output current, eg: 25A out of a "70A" alternator. This will be easily enough to run your fridge and put a reasonable charge into the batteries simultaneously.

 

Chris

[honey ryder]

wouldnt a bigger pulley on the alternator make it turn abit faster for lower revs.. therefore providing more charge when on tickover or when cruising slowly?

 

we use our travel power to charge our batteries, basically thats 240v from the big engine alternator, going into the battery charger that either charges from travel power, a generator or shore power. we have a beta 38 engine too, but only 3 x 110 batteries. it takes us around 1.5 hours per day to charge our batteries.

Edited August 29, 2007 by honey ryder

[bottle]

wouldnt a bigger pulley on the alternator make it turn abit faster for lower revs.. therefore providing more charge when on tickover or when cruising slowly?

 

we use our travel power to charge our batteries, basically thats 240v from the big engine alternator, going into the battery charger that either charges from travel power, a generator or shore power. we have a beta 38 engine too, but only 3 x 110 batteries. it takes us around 1.5 hours per day to charge our batteries.

 

Whoops!!!!!!

 

other way round, larger pulley on engine or/and smaller pulley on alternator but beware of belt 'bite' (wrap), I believe the belt should be in contact with two thirds of the pulley groove.