split charge relay

[Moisha]

Hi All,

 

We want to use a split charge relay in order to make use of both our alternators.

 

The engine has two 80 amp alternators. We have one starter battery and a bank of four 110amp/hour leisure batteries.

 

We want to arrange it so that there are the following possible charge states:

A) 1 alternator charging the starter, 1 charging the battery bank.

both charging the battery bank (when the starter is full)

 

We've been told that the relay wil switch automatically from A) to when the starter is full. Is that right?

 

What spec should the relay have? Is it enough to get a 160+ amp, 12Volt relay?

Or must the relay be capable of accommodating power surges?

 

Does anyone recommend a particular make or type of relay?

 

If anyone can advise quickly, we'd be very grateful - we must order it today so that it comes by Monday (our sparky friend is coming back on Monday expecting materials and beer).

 

J+A (Moisha)

[KenK]

Hi Moisha,

 

Have a look at Gibbo's website www.smartgauge.co.uk. Loads of useful information written for non techies.

 

Ken

[Moisha]

Hi Ken,

I have the smartgauge monitor, but they do not sell the relays themselves. I've been looking into this and it seems relays are used to split charge from a single source (1 alternator), but I am completely confused when it comes to hooking up our 2-alternator system and sending the charge from both alternators to the domestic bank only when the starter battery is full.

 

I found some rather cheap relays rated at 180 amps. Would that do if we are hooking up 2 80amp alternators?

 

Continually confused,

moisha

[David Schweizer]

Whilst i am not an expert on these matters, I seem to recall that when this subject has been raised before, the "experts" have always advised that what you want to do cannot be done (well not easily). If you have two 12v alternators on your engine, one is to charge the Starter motor, and the other is to charge your Cabin batteries.

 

What I suppose you could do is replace one of them for a higher output unit to charger your cabin batteries, but from my experience even a 55 amp alternater on full output places a hell of a strain on the belts.

[Theo]

Whilst i am not an expert on these matters, I seem to recall that when this subject has been raised before, the "experts" have always advised that what you want to do cannot be done (well not easily). If you have two 12v alternators on your engine, one is to charge the Starter motor, and the other is to charge your Cabin batteries.

 

What I suppose you could do is replace one of them for a higher output unit to charger your cabin batteries, but from my experience even a 55 amp alternater on full output places a hell of a strain on the belts.

 

I think that this arrangement may well be what you want: http://www.tb-training.co.uk/twinalt.html#...0VOLT%20SYSTEMS.

 

HTH

 

Nick

[Moisha]

It is indeed the simplest thing to do wire one alternator to starter and another to domestic battery. But we thought that being able to charge the domestic bank from both alernators when the starter is fully charged would maximize our use of the alternators which would be extremely useful since we are live-aboards nad cruising continually. The straight-forward thing of course is to hook up one alternator to starter and another to domestic battery.

 

But we thought we could try to get a little fancy with it.

 

thanks for all your replies.

moisha

[Tony Brooks]

It is indeed the simplest thing to do wire one alternator to starter and another to domestic battery. But we thought that being able to charge the domestic bank from both alernators when the starter is fully charged would maximize our use of the alternators which would be extremely useful since we are live-aboards nad cruising continually. The straight-forward thing of course is to hook up one alternator to starter and another to domestic battery.

 

But we thought we could try to get a little fancy with it.

 

thanks for all your replies.

moisha

 

 

Indeed this is the simplest way, but if you fit a simple split charge relay between the two batteries energized by the ignition switch or better still by one alternator's output you will charge both battery banks at once. each bank will automatically take the proportion of the total charge it needs based upon the bank's terminal voltage and the charging voltage.

 

This is simple with only a simple addition to most systems.

 

By all means buy Gibbo's split charge relay to do the job, but unless I had a large Leece Nevil (140 amp) alternator i would stick with a Du rite or Lucas relay (being a tight wad) and check its voltdrop occasionally first thing in the morning.

 

You have been pointed to the diagrams and if you want one that dooes not "hide" c able email me.

[bottle]

I think there may be some confusion arising here because of terminology.

 

Moisha has two alternators of 80amp each, one charging the starter and one charging the domestics.

 

Moisha does not require a split charge relay. (as I understand it)

 

Moisha requires to combine the the two alternators outputs, so as to charge the domestics quicker.

[Cafnod]

That is how I understand Moishas post too Bottle.

Sterling sell a gadget that does this, I guess it uses diodes.

As an alternative we have taken one alternators output straight to a bank of 2 X 110 ah batteries that feed the domestic 12vdc services. Fully charged our needs are met for about 7 days by this.

The second alternator goes to a splitter and then charges the starter battery and a further pair of 110ah domestic batteries which run a 1850 watt inverter.

This will happily keep the fridge and our fairly simple 240vac needs for about 3 - 4 days.

It seemed the easiest way to do it and has many advantages for us.

[John Orentas]

Hi Moisha.

 

Your present system with two alternators is by far the most elegant system it is possible to have, with one alternator looking after your domestic electrical system and another for you starter battery you have two totally independent systems with all the advantages that that implies and an 80 amp unit is more than adequate for charging a bank of 4 x 110 a/h batteries, you have no need of split charge relays, diodes or even controllers, but you must bear in mind every alternator has it's own controller built into it. If however you were to connect them together in some way you would loose all the advantages of the system you have, one dud component will be likely to take out others and you would be vulnerable to having failures of your entire electrical system.

 

The kind of 'hanging by your fingernails and living on the edge' philosophy that some members here advocate (for other peoples boats) may be all very well if you are racing motorcycles round a track but I would suggest completely out of place on a narrowboat.

Edited April 22, 2007 by John Orentas

[Canal Shop Man]

Having one alternator just charging the starter battery is almost a complete waste of money! After about 5 mins, it has done its job and serves no useful purpose.

As suggested above, the Sterling bit of kit will divert this power to the domestics when the starter battery is fully charged. See Battery to Battery Digital Charger for further details.

We have one in stock if you can get to us and still need it for Monday!

[Tony Brooks]

I think there may be some confusion arising here because of terminology.

 

Moisha has two alternators of 80amp each, one charging the starter and one charging the domestics.

 

Moisha does not require a split charge relay. (as I understand it)

 

Moisha requires to combine the the two alternators outputs, so as to charge the domestics quicker.

 

 

Each alternator is supplying one battery bank - I think we agree on that.

 

Moisha wants to make both alternators charge the domestic bank so he gets a higher charge rate and therefore a faster charge.

 

The simplest way is to use a high current relay (which most people would call a split charge relay) to join both battery bank positives together when the alternators are charging, unfortunately to ensure both are charging becomes over complicated because until a fault occurs they both will be. The relay contacts are connected so they join the battery positives and the relay is energized from either a suitable alternator terminal or the ignition switch.

 

The bank negatives should be joined anyway (to the hull earth point).

 

When the alternators starts to charge each will see one large bank with some batteries more discharged than others. each battery will accept the correct proportion of the available charge based upon the difference between their terminal voltage and charging voltage.

 

Unless there is something wrong with the engine the starting battery will be very fully charged so the bulk of the output from both alternators will go to the domestic battery.

 

There may be a problem if one alternator is set to a very much higher charging voltage than the other, but about £20 for a relay makes a cheap first try and there is every chance it will work.

 

There was a thread on the possible problem some time ago.

 

Tony Brooks

[Moisha]

Hello all--thanks for all the very useful advice. We sort of decided to get Gibbo's kit for this. We will be cruising continually. So--what the hell--might as well get the right equipment. We have already bought his smartgauge that can be hooked up nicely to the diode gizmo. For the moment we are charging each battery (bank) off their own alternator. But I do think that (as has been pointed out), it is wasteful to devote 1 alternator solely to the starter battery.

 

Hopefully the system will be hooked up in a week or so and we will let you all know how we get on.

 

Also--John, could you tell me more about the technical details of problems that may arise from such an arrangement? You can use techie talk as I will forward it to my sparkie friend.

 

Cheers and thanks a million again.

moisha

[John Orentas]

I thought I already did, but good luck with whatever you buy.

[anhar]

We sort of decided to get Gibbo's kit for this. ...We have already bought his smartgauge that can be hooked up nicely to the diode gizmo...

Note that the SmartGauge must be connected direct to both the positive and negative battery terminals of the domestic batteries and similarly to the starter battery, not to the "diode gizmo". It must not be connected anywhere else in the circuit. This is absolutely critical for the device to operate correctly according to the company.

 

I presume by the other kit you are referring to the SmartBank which is their alternative to other battery paralleling devices like diodes and relays. Note that the version you should get is SmartBank Advanced which does exactly the same job but can be connected to SmartGauge thus allowing remote control and monitoring features.

 

regards

Steve

Edited April 23, 2007 by anhar

[Sir Nibble]

First, is your domestic charging alternator spending long periods of time at it's maximum output? If not, you have no need of additional generating power. If it is then a 180A relay connecting both batteries when the alternators are charging will provide output from the starter battery alternator to assist. The alternators will not interfere with one another, nor will you risk running your starter battery flat.

I understand the difficulties in accepting at face value a comment like this when big price tags on add-on equipment suggest a far higher level of complexity. I am an auto end marine electrician with over 30 years of experience, I have worked on systems designed with twin alternators connected together, it works, and will continue to work even if mathematically proven to be impossible.