Voltage Sensing Relays - Opinion sought!

Ben_e_Toe

Ben_e_Toe

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I have a simple two battery system with a single charging source and only basis interior/exterior lights, autopilot and NAV gear running from the domestic bank. Currently there are two battery isolators and a 'charging' switch to bridge the batteries together when the engine is running. The Merlin VSR seems to be a good solution to automate the process of switching the 'charging switch' for me and remove the risk of leaving the batteries in parallel when the engine is off.

That said, does anyone out there have/use a VSR in this way? Do you rate them as a device and are there any drawbacks. At £65 a pop I want to make sure that they are a good investment. Any help gratefully received.......
 
I changed from a split diode system to VSR two years ago, charging into two battery banks of 240 AHrs and 120 AHrs via an adverc smart controller from an alternator and also an air X generator, monitored with a link 2000. It does exactly what it says on the box and has worked faultlessly with the advantage of lowering the charging voltage by 0.6 volt ( no diodes to overcome). It will certainly do what you want in terms of removing the necessity to manage your charging manually.
 
For a system just as you describe, a VSR would be suitable and is used by many people. There can however be difficulties if you are running heavy draw devices like windlasses just after starting the engine on a morning following a long nights drain of lights, TV & Fridge. I use one to charge the in-car fridge battery that we use when driving across Europe to Corfu but with our heavy demand wouldn't use one on our particular boat.

For boats the common device is the diode splitter but without some sort of boosting alternator controller, a voltage drop can be expected, although modern "low loss" diode packs go some way to eliminate or at least reduce this.

Another device is the Battery Charger & Changer which uses one battery's power, converted to a high enough voltage to charge another battery allowing each to supply it's own circuit independently. These are popular in the USA & compulsory on Commercial & Charter boats in this country to ensure a protected supply for the distress radio if no dedicated on-board generator is available.

For your situation, as described, a VSR would be entirely suitable.

Steve Cronin
 
The situation you describe is only likely to happen if one parallels the starting battery and the domestics and drains them both, in which case you may have trouble starting the engine and no charging setup will protect you from such a mistake. If you isolate the starting battery from such a drain the VSR will quickly charge into both battery banks after replacing the relativly small charge consumed in starting the engine and should be sufficient to allow the windlass to operate. Unless you have been foolish enough to take the domestic batteries below 50% charge which if is the case your batteries will not last too long and you will have other problems.
 
Steve

Quote
There can however be difficulties if you are running heavy draw devices like windlasses just after starting the engine on a morning following a long nights drain of lights, TV & Fridge
Unquote

Just to clarify your concern is it that the amperage through the relay from the heavy load could be max output of alternator plus additional amps from the charged starter battery? If so this could be limited by a suitably rated breaker in series with the relay.

I have a VSR arrangement but without any large load potential.
 
Before....

...you start telling me what is going on with my own boat, kindly READ what I posted.

And YES I WILL be foolish enough to take the batteries too low on occasion - this is a serious live aboard vessel not a weekend plaything. Sometimes, food preservation and/or the ability of a lady crew to raise the anchor CAN result in a heavy drain being pulled up the charging cables when paralleled by a VSR which is why I wouldn't use a device not suited to the purpose to which I need to put it (Specific application) The boss of Adverc once told me of tales of these devices being melted when used in the wrong place - in his case it was ambulances.

VSRs have their uses but my application is not one of them. Yours may be fine.

Steve Cronin
 
Yes it could but then you're designing the system around it's physical limitations NOT your in the field requirements - (like a 70s British sportscar!). When the hook needs to come up it's no good saying to the lady crew that she needs to get the handle out because the trip has flipped. It's the current able to get across the paralleled charging wires from one battery to the other that is the danger. With diodes, it just can't.

Steve Cronin
 
VSR sizing...

Steve Cronin has described a scenario in which the current through a VSR can be much larger than usual. The possibility of this happening can be anticipated, and if there's a likelihood, the VSR can be sized appropriately. BEP make a 100A VSR which can take 140A intermittently, and they also make a heavy-duty 300A VSR which will take 1500A for 10 seconds. One of these would cope with most eventualities.

It wouldn't be a good idea to put a breaker in series with a VSR.
 
Re: VSR sizing...

Thanks for your comments, seems that VSRs are useful. I don't have an electric windlass or fridge (wish I did) so I don't think the maxium load will be a problem. Just to check the point on an earlier post, do I have to match the VSR rating to the maxium charge from the alternator or the maxium draw from all of the loads. (PS I have a Volvo 2001 with a bog standard alternator).

On the cost point, I was quoted £49.99 + £5.80 p&p + vat = £65!
 
Ok if you fit wrong sized equipment, but by supplying the winch from both batteries and the alternator, it maintains a far higher supply voltage to the winch. This in turn will give a lower current draw than with the low domestic battery suppling the winch. If the draw is too great the voltage will fall and the relay will drop out anyway, and with 200 - 1300 amp capacity for winch load you do not need a circuit breaker.

Brian
 
I suppose it does depend on how you look at. On my last boat, a sports cruiser, I replaced the broken 1/2/both switch with a bank of switches which included a VSR. It all seemed to work OK.

My current boat, a simple fisher with two batteries, has a relay to connect the house battery to the alternator when the engine is running. When the engine is switched off then the batteries are separated.
 
Re: VSR sizing...

[ QUOTE ]
do I have to match the VSR rating to the maxium charge from the alternator or the maxium draw from all of the loads

[/ QUOTE ] In theory, you need to size the VSR for whichever is the higher. From the info you've given, a 100A VSR would be fine.

On price, you can get a 100A VSR from Quaywest-Online for £55 inc VAT and UK delivery.
 
I fitted one of Merlin's BEP VSRs last year and it's worked perfectly. No more need to juggle switches before / after starting the engine, no risk of blowing alternator diodes by getting the sequence wrong, and no more electronics drop-outs when pressing the starter button. No energy wasted by splitter diodes either. Highly recommended. For slightly cheaper solutions, see previous threads on using a relay driven by an engine auxiliary, e.g. oil pressure switch, to parallel the batteries: personally, I think that the additional benefit of the operating voltage hysteresis built into the VSR outweighs the extra cost - and it looks nice too!

I'm tempted to enter the heated discussion on supplying windlass current by suggesting that what has been said so far would lend support to the (unpopular) option of using a dedicated battery for this job ... but I won't! (Runs for cover ...) /forums/images/graemlins/smile.gif
 
Then...

.....you don't have the potential for a problem.

Consider what would happen if you put a load like a windlass (mine pulls 125 amps) or a bow thruster (not quite so bad in most cases as they don't often stall) through NOT the usual heavy, say 50sqmm cabling but down the (say 6sqmm) charging wires and also across the contacts inside a 60amp (or even a 120amp - although this will probably not itself be harmed) VSR

That is the potential danger scenario when the two batteries are paralleled after the initial charging period.

Steve Cronin
 
So long as.....

...you replaced your charging leads with appropriately oversized ( welding?) cable. Not many people will do this. They are far more likely to just drop the unit into place as a replacement for the splitter diodes.

Steve Cronin
 
It wasn't actually me who recommended Quay West, but if their's is the unit I think it is it doesn't have any quoted hysteresisis, i.e. the pick up and drop out voltages are nominally the same. (OK, they can't be exactly the same or it would chatter, so slightly different in reality.)

If you don't mind forgoing useful hysteresis and aren't fussy about appearance, there's a French make of (much cheaper) VSRs in vehicle relay type packages which Merlin used to also sell - don't know if they still do.
 
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