twin alternators

[secret squirrel]

Hi

we have twin Lucas 127 alternators one for start battery the other for dom batteries (5x110amp) would we benefit from a merlin smart bank with split charger (we already have smart gauge).

Thanking you all in advance.

Cheers

[by'eck]

It depends what you wish to do. If its to utilise both alternators effectively in parallel to maximise their charging potential to both banks then something like a Sterling alternator to battery charger (AtoB) may be more appropriate and easier to fit as well as boosting the output of both alternators.

 

The two alternators would then work in parallel charging the domestic bank with a second isolated charge feed dedicated to the starter battery. Just make sure that you choose an AtoB model that can handle the combined max current of both alternators. Having matching alternators will help as well although not essential.

[dmr]

Alternator paralleling can be very effective and you can do it with just a big relay and a switch, but you MUST remember to turn it off when you stop the engine.

I am sure there used to be a huge pinned thread on this topic with all sorts of circuit ideas, I have just looked at the pinned alternator paralleling thread and its much much shorter than it used to be, does anybody know where all this useful stuff has gone???

 

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

[nicknorman]

For a simple cheap solution why not permanently connect both alternators to the domestic bank and use a spilt charge relay (coil connected across one of the alternators' warning lighs) to charge the starter battery.

[secret squirrel]

Thanks guys

Is the smartbank not the way to go what with me already having smart gauge fitted and working and the smartgauge at a price i can afford.

 

cheers Chris

[nicknorman]

Thanks guys

Is the smartbank not the way to go what with me already having smart gauge fitted and working and the smartgauge at a price i can afford.

 

cheers Chris

Yes there is nothing wrong with using the smart bank. I can't remember how much it costs but for some applications it seems a bit overkill. A split charge relay such as I mentioned will set you back about £30.

[Sabcat]

For some reason (I might have dreamt it) I think that only one alternator will charge when they're in parallel, which ever is making the most current.

[by'eck]

For some reason (I might have dreamt it) I think that only one alternator will charge when they're in parallel, which ever is making the most current.

 

Not when there are both operating below their respective voltage regulators limit. This will lead to a situation eventually though where there becomes a dominant one as the batteries approach full charge effectively shutting the other down temporarily. This is unlikely to be an issue since the batteries wouldn't be drawing sufficient current to justify both anyway.

 

The OP having similar alternators will minimise this issue assuming they have the same voltage regulation points.

[secret squirrel]

The smartbank is about £130 and from what i have read its totally automatic, and gives all error notifications the wiring of it looks quite simple, so once fitted it can be forgotten, i already have all cable and connections, i like to keep a check on what is happening battery wise so the smartbank looks the way for me.

 

cheers Chris

[secret squirrel]

Both alternators join to the same regulator is this correct? or would it be better to have separate regulators with the same settings?

 

cheers Chris

[secret squirrel]

Sorry but ignore that last message, the two live leads form the alternators go to separate buzz bars from each bar a live lead connects to a lucas box which is about 45mmx30mm plus there are two common wires connected to the box does anybody know what the box is please?.

 

Cheers Chris

[nicknorman]

Sorry but ignore that last message, the two live leads form the alternators go to separate buzz bars from each bar a live lead connects to a lucas box which is about 45mmx30mm plus there are two common wires connected to the box does anybody know what the box is please?.

 

Cheers Chris

Its a bit hard to tell from your description (a photo would help) but it sounds very much like a split charge relay. If you can't post a photo, describe all the markings on the box.

[secret squirrel]

Just googled it, it seems to be a relay but only 60amp so is it split charge? combined amps would be in the region of 130amps and live lead from relay is only 7mm so at most what 20amps also other side of each buzz bar is a heavy duty live cable going back the battery terminals one on start and one on dom, there is only the number 0209 + lucas on box.

 

Cheers Chris

Sorry but how do i send pictures.

 

Cheers

[secret squirrel]

Got to have dinner will sort out some picys later thanks for your patience.

 

Cheers Chris

[nicknorman]

Slightly losing track of your description - it's hard without a diagram! To post a photo, you first need to upload it to a photo website like Flickr, photobucket etc. Then you post a link to it. There are a few threads in the technical and account support section of the forum on how to do this.

 

Anyway, it still sounds like a split charge relay! I agree the relay seems under-specced but by using smallish cable there is probably sufficient resistance to keep the maximum current down. Anyway, if there is already a split charge relay there is not a lot to be gained by adding a smart bank, but of course if you have plenty of money, why not!

 

A really good way to get a handle on what is going on, is with a DC clamp meter. You can clip these over the various cables and measure the current in a jiffy. The UT-203 can be had on ebay for £30 and has a 40A and a 400A range.

[by'eck]

Just googled it, it seems to be a relay but only 60amp so is it split charge? combined amps would be in the region of 130amps and live lead from relay is only 7mm so at most what 20amps also other side of each buzz bar is a heavy duty live cable going back the battery terminals one on start and one on dom, there is only the number 0209 + lucas on box.

 

Cheers Chris

Sorry but how do i send pictures.

 

Cheers

 

So it looks like this?

 

 

If so yes its a 60 amp single pole relay with main contacts normally open. Contacts 85 and 86 are the low current coil connections which when fed with 12 volts energise coil to make a high current (60 amp max) connection between the switching terminals labelled 30 & G.

 

From what I understand you have two of these each connected to one of the two alternators you have. With above info you should be able to decide if you already have a split charging system triggered when the engine is running to parallel the starter battery with the domestic ones. The 60 amp rating is inadequate for 65 amp alternators though even if such currents are never passed.

 

If you decide to re-engineer the system with paralleled alternators (and don't want to take the admittedly expensive Sterling AtoB option), their positive output cables need to be fed together to the domestic battery bank positive and also to one of the main contacts of a 150 amp relay (better to be over-rated) with the other main contact to the starter battery positive, such that when triggered by the engine running as nicknorman suggests, parallel's the starter with domestic bank.

 

The Smartbank option while seemingly more attractive will offer little more in performance.

 

ETA: the main connections from alternators to batteries and relay need to be of suitable gauge battery cable - 35mm² as a minimum should be adequate if its a short cable run.

Edited October 11, 2014 by by'eck

[dmr]

I much prefer to have each alternator connected to its own bank, then use the relay to join the banks, that way if the shorting relay is not engaged for whatever reason the starter battery still gets a charge. It also allows different absorption voltages on the domestic and starter banks if required, though you have to turn off the relay after bulk charge to do that. I assume this is the stuff that the Smartbank does.

 

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

[secret squirrel]

Hi

https://www.flickr.com/photos/128592203@N06/15507263912/

Thanks nicknorman anticipated the need for ampmeter bought one from machine mart today.

Thanks Richard, what happens to the low voltage leads?

 

Cheers guys

 

Chris

That how i believe the smart bank does it.

[nicknorman]

I much prefer to have each alternator connected to its own bank, then use the relay to join the banks, that way if the shorting relay is not engaged for whatever reason the starter battery still gets a charge. It also allows different absorption voltages on the domestic and starter banks if required, though you have to turn off the relay after bulk charge to do that. I assume this is the stuff that the Smartbank does.

 

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

Yes, but on the other hand your way puts a lot of current through the relay for a long time. Swings and roundabouts?

[dmr]

Yes, but on the other hand your way puts a lot of current through the relay for a long time. Swings and roundabouts?

 

Yes, I knew somebody would point that out.

It also puts a bit more resistance into the harder working domestic route.

My installation is particularly bad because I turn it on manually so the relay switches the heavy current too.

Its a cheap and cheerful Durite relay and has lasted 3 years so far.

My big concern would be loosing the charge to the starter battery which is why I have done it this way.

The starter alternator is quite a little thing, I might put a bigger one over the winter, and this well prove your logic to be correct!

 

...........Davei

[by'eck]

I much prefer to have each alternator connected to its own bank, then use the relay to join the banks, that way if the shorting relay is not engaged for whatever reason the starter battery still gets a charge. It also allows different absorption voltages on the domestic and starter banks if required, though you have to turn off the relay after bulk charge to do that. I assume this is the stuff that the Smartbank does.

 

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

 

Better to engineer a system that works most efficiently with least strain on components when there isn't a fault, rather than weakening the system to cover an unlikely contingency. In any case you already have redundancy if one of the paralleled alternators fails to provide output current.

[nicknorman]

Better to engineer a system that works most efficiently with least strain on components when there isn't a fault, rather than weakening the system to cover an unlikely contingency. In any case you already have redundancy if one of the paralleled alternators fails to provide output current.

The voice of design wisdom!

[by'eck]

Hi

https://www.flickr.com/photos/128592203@N06/15507263912/

Thanks nicknorman anticipated the need for ampmeter bought one from machine mart today.

Thanks Richard, what happens to the low voltage leads?

 

Cheers guys

 

Chris

That how i believe the smart bank does it.

 

I think you refer to the thinner relay energising coil cables. I can only suggest you confirm by tracing the present wiring since your picture doesn't help in that respect. If you re-engineer with a single relay of suitable current capability and triggered as suggested that would IMO be the best option.

[dmr]

 

Better to engineer a system that works most efficiently with least strain on components when there isn't a fault, rather than weakening the system to cover an unlikely contingency. In any case you already have redundancy if one of the paralleled alternators fails to provide output current.

 

I think my needs are maybe a bit different to the OPs.

I have a bank of Trojans that I charge off the bigger alternator and the Adverc brings the voltage up to 14.8,maybe 15 in winter (I adjust it).

The smaller alternator does the starter battery at about 14.5v.

If we are doing a big cruise I don't even engage alternator paralleling. If running the engine just to charge the batteries I will join the alternators to help with the bulk charge then hopefully disengage later to reduce water loss in the starter battery. I might automate all this at some stage but I quite enjoy looking at ammeters and turning things on and off, I am a sad engineer.

We have lived off grid for a number of years now and it works for me. The Trojans are three years old at the end of this month and I will put a progress report on this good forum.

 

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

[GUMPY]

I went this way

90a prestolite charging domestics 3x120ah sealed

70a ACR charging starter 1x 120ah sealed

30a mains charger on domestics

VCR with the sense wire connected to domestics.

Works like this

connects when domestic voltage is above 13.2, disconnects at 12.8.

So the one landline charger keeps both domestics and starter on float at 13.6 whenon the moorings.

Connects both banks when domestics go above 13.2 so get both alternators charging all batteries.

Also get to make use of a small % of starter battery for domestic use until the voltage drops below 12.8v and there is still plenty left in there to start the engine.

Smartgauge does get slightly confused as it usually still reads 100% after an evening of tele etc. Only when the VCR drops out does the percentage start to drop.