Twinning up alternators

[Roger Gunkel]

Apologies if this has been covered before, but life is about to change and I am looking at ways to increase our charging.

 

After being liveaboards on a marina based residential mooring for eight years with shortish trips away from base, we are going to be leaving the luxury of mains hookup, for an extended period of off grid living. I will be extending our existing 200 watts of solar pv to 500 watts, but as the engine is fitted with two 75 ah alternators, wondered whether it is possible to disconnect the output of the starter battery alternator and connect both alternators to the domestic bank. If so, is it just a simple matter of paralleling up the outputs, or will this lead to damage to one or both alternators? Hopefully if this is possible, it will considerably shorten the bulk phase of the charging process of the 500ah battery bank in the short term, with the solar giving a lower sustained output for the later charging stages.

 

I am not worried about flattening the starter battery, as there will be another 100w solar panel permanently connected to it, plus a back up battery kept in charged condition.

 

All batteries will be new as they are all due for replacement, all lighting will be leds and we will be replacing any high consumption appliances.

 

Roger

[Chris Pink]

http://www.canalworld.net/forums/index.php?showtopic=33065

[Arthur Brown]

Paralleling alternators works, it increases the bulk charge rate as you say. It's likely that your starter battery will be recharged from an engine start within 15 to 20 minutes -assuming good condition and an average start cycle.

 

Ensure that the reserve battery gets some charge every few days, remember that it will self discharge in 100 days. This means that it should be given an amphour most days or an hour on an auto alternator most weeks OR it's own small solar panel (with regulator if it's a sealed battery ).

 

As a longstop on the backup plan, I'd still have a string pull generator sitting there in case, and if you can fins a 600w two-stroke one for as cheap as the last one mentioned on here (£50) it would be small in the engine room til you need it.

 

Sadly solar panels need light which is in smaller supply in the winter, the last data published on this site was that winter electricity from solar is just less than 10% of the summer output.

[blodger]

I would have thought that a safe and easy way to parallel your alts would be to fit a voltage regulated relay (about 30 squid on Ebay) to in effect connect both alternator outputs once the starter battery reaches 13.2 v or so.

 

I do not have a VSR but added a second alt relayed into the domestics adding to the conventional split charge relay set up.

 

ETA I have since ditted cheapo 100amp shunted analogue ammeters into the alternator output cables so that I can see that both alts are charging simultaneously all the time.

Edited August 6, 2012 by blodger

[nb Innisfree]

Yes Roger just

simply parallel both alternators and connect them to your domestics only, when acceptance voltage is first reached one alternator will shut down leaving the other to carry on with absorptio, no damage. Assuming you have an inverter connect a small trickle charger for seperate starter batt for non sunny days.

[by'eck]

FWIW I have one alternator dedicated to feeding the service bank and the other feeding all three banks via a Sterling zero volt drop splitter. This offers redundancy for charging the most important service bank. The splitters are available in a range of single or dual alternator input/two to four output versions with a range of handling currents. Click on image.

 

 

The splitter has a dedicated connection for external sensing if your alternator allows it or you are using an external DAR. This overcomes the problem of sensing on only one of the banks it feeds, allowing equal charge volts to all three banks, although not acknowledged by Gibbo on his treatise on alternator split charging.

 

It also offers priority to starter, service then bowthruster bank (if you have three output version). There is a high drain override (backfeed) on any bank, if operating the bowthruster for example, where it feeds the needy bank exclusively. Since my 90 amp alternator blew a 100 amp fuse in the BT bank charge feed, I have to assume all the bits are working happily together

[Biggles]

Hello Roger.

 

I did mine Linky

 

If you want to have a look and or discuss it PM me for my phone No. We aren't far away from you.

[bottle]

All the above assumes that both alternators are the same voltage.

 

ie. both 12v or both 24v nominal.

Edited August 6, 2012 by bottle

[Roger Gunkel]

Hi guys, apologies for not getting back sooner, internet connection has been down this morning Thanks for the replies and it seems that my idea is pretty straight forward and workable.

 

Thanks Chris for the link to the previous thread, particularly Gibbo's emphatic post which seems to confirm my own thoughts.

 

Arthur, I have been running 200w of solar for the last couple of years, and I am quite sure that we will manage with the increase to 500w + 100 backup, and our wind generator which I had forgotten to mention. The paralleling of the alternators will give us a good extra boost through the Winter with our greatly reduced electrical consumption. My experience with solar is that the figure of 10% is based on estimated optimal highs and minimal lows, but in actual real life use, we have been getting more than that through the winter as optmal levels are rarely reached at both end of the scales.

 

Bottle, both alternators are identical which should make paralleling an easy option and a cost free increasing of the charging rate. I've never seen the point of a 75ah alternator to charge a starter battery that is used for maybe 5 seconds a day.

 

Blodger, Innisfree, By'eck, Biggles, thanks for the input, I think I will keep it as simple as possible at the moment, literally just attaching the alternator outputs to the same bank terminals, before going down a more electrically sophisticated route. As Gibbo said, the alternators already have enough built in electrics to sort themselves out.

 

Roger

[bottle]

Roger

 

My post was not really aimed at you, just to make it absolutely clear to anyone that does not have the knowledge you do and may read the thread at a later date..

 

I cannot parallel mine as they are different voltages.

[Timleech]

 

It also offers priority to starter, service then bowthruster bank (if you have three output version). There is a high drain override (backfeed) on any bank, if operating the bowthruster for example, where it feeds the needy bank exclusively. Since my 90 amp alternator blew a 100 amp fuse in the BT bank charge feed, I have to assume all the bits are working happily together

 

Not sure what you mean by 'high drain override', but if your 90A alternator blew a 100A fuse, I suggest that the alternator probably had some help from somewhere else.

 

Tim

[Roger Gunkel]

Roger

 

My post was not really aimed at you, just to make it absolutely clear to anyone that does not have the knowledge you do and may read the thread at a later date..

 

I cannot parallel mine as they are different voltages.

 

I didn't take your post as being a warning for me particularly Keith, and it is a very valid point that the alternators need to be matched. I am flattered at your suggestion that I have a good level of electrical knowledge but my knowledge is pretty basic based on information gleaned here and trial and error. I am always happy to listen to those who have already been where I am heading

 

Roger

[Smelly]

After the paralleling experiment i ended up with a switch until i got some money and installed a Smartbank. It does the trick!

[smileypete]

I've never seen the point of a 75ah alternator to charge a starter battery that is used for maybe 5 seconds a day.

If that's the case maybe put both alts on the domestic bank, then charge the starter batt with a DC-DC constant current converter:

 

http://www.ebay.co.uk/itm/350553798847

 

Bear in mind if both alts are on one bank, one alt light may come on if it's output current drops to zero before the other alt.

 

cheers, Pete.

~smpt~

 

Edit: Oops just echoing what nb Innisfree said.

Edited August 8, 2012 by smileypete

[Roger Gunkel]

If that's the case maybe put both alts on the domestic bank, then charge the starter batt with a DC-DC constant current converter:

 

http://www.ebay.co.uk/itm/350553798847

 

cheers, Pete.

~smpt~

 

That's a good idea Pete, although I will be keeping the starter battery charged with a 100w solar panel that I already have. Could be useful for others though

 

Roger

[Gibbo]

The splitter has a dedicated connection for external sensing if your alternator allows it or you are using an external DAR. This overcomes the problem of sensing on only one of the banks it feeds, allowing equal charge volts to all three banks, although not acknowledged by Gibbo on his treatise on alternator split charging.

 

I think you have horribly misunderstood:-

 

A. What I wrote.

B. What the equal charge volts refers to and

C. What the sense input does on the Sterling unit.

 

PS... http://www.urbandictionary.com/define.php?term=sence

Edited August 9, 2012 by Gibbo

[by'eck]

Not sure what you mean by 'high drain override', but if your 90A alternator blew a 100A fuse, I suggest that the alternator probably had some help from somewhere else.

 

Tim

 

Yes your right. Later discovered that the backfeed override designed to inhibit backfeeding from other banks, has a finite time before it operates. A design feature to reduce relay chatter.

 

Nevertheless as the engine limps somewhat when I operate the thruster I'm guessing its providing a big chunk of the current.