VSR or Split charger?

NickRobinson

NickRobinson

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Hi-
(too much time on my hands, obviously...)

Marine VSRs seem to cost £70/100 ish

'Camper' split chargers £10/15.

I know the latter are 'dumb', simply connecting the batteries together when the engine is running (works on my camper OK)

So is this a bargain? Can it be truly intelligent/sensing?

http://www.ebay.co.uk/itm/SPLIT-CHA...ccessories&hash=item19d37e3029#ht_2824wt_1062

Now I can waste you time too.... :D

Nick
 
NickRobinson said:
So is this a bargain? Can it be truly intelligent/sensing?
Click to expand...

It all depends on what you want to do :)

If you have a small 30 amp alternator and 50 amphour battery second battery, it may well be fine.

If you have a 100 amp alternator and 250 amphour service battery, it's not good.

It is is a basic VSR, avoiding over charging is marketing, you will no more over charge the service battery as you will the engine battery.

What do you want to use it for ?

Brian
 
VSR

I think you will find the VSR in the link just fine. As for it sensing the state of the receiving battery I very much doubt that but it doesn't matter.
If you are concerned that you might want to charge the house battery at more than 30 amps then a little resistance in the line for charging will give more protection.
I would not bother but a resistor of .1 ohm will drop 3 volts at 30 amps which would probably cope (keep the charge current less than 30 amps) with a battery of 10volts or so. Or you could fit a 30 amp fuse in the charge line and accept that you may have to replace the fuse if the house battery is that low that it wants to charge at more than 30 amps. Or fit a .1 ohm resistor in parallel with 30 amp fuse so only putting resistor into play if battery is really low so blowing fuse. Note resistor might have to dissipate a few hundred watts at initial charge. But with fuse blown battery will be charged at a lesser rate at least initially.
I would suggest a plate of stainless steel 300 mm long 10mm wide of 18 gauge with bolt hole in each end would make a reasonable resistor. Mount it so that if it gets red hot it won't set fire to the boat. (highly unlikely it will get that hot but be safe)
All this might seem way out so just fit a 30 amp fuse and perhaps fit a car headlight globe across the fuse to give you some charge if fuse blows. Without a fuse or resistor it might survive a very flat battery and huge charge as that will only occur for a short time. If it melts well no great loss.
Or yet another idea is to use the VSR to operate a large current relay to join the batteries. This relay could double as emergency start relay. Good luck olewill
 
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nimbusgb said:
Durite VSR £38. Had one fitted to our boat for 3 seasons now. No problem.

And why disconnect it when shore power is attached? It doesn't matter where the charge is coming from!
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Helpful replies, especially Olewill's!

That durite item can be found down to 26 pounds +pp now.

No action by me until lay-up, then some rat's nest wiring to tidy..

Nick
 
snooks said:
If you have a dual output charger, you just use one of the outputs and connect it to the engine battery.....That's what my instructions told me to do, so that's what I did :D
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Doing this totally negates the benefit of dual independent (as opposed to split) outputs. Perhaps your charger is a split type with isolating diodes. My charger is essentially two side-by-side chargers, at least in the output stages.
 
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nigelmercier said:
Doing this totally negates the benefit of dual independent (as opposed to split) outputs. Perhaps your charger is a split type with isolating diodes. My charger is essentially two side-by-side chargers, at least in the output stages.
Click to expand...

That sounds like a useful bit of kit. What make/type is it ?
 
VicS said:
That sounds like a useful bit of kit. What make/type is it ?
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I've just re-read the manual, and it seems the technical department lied; the outputs are diode split. However, the other reason for not shorting the outputs with the VSR is because this would alter the voltage on the sense wire, so my modification to the VSR is still valid.
 
nigelmercier said:
I've just re-read the manual, and it seems the technical department lied; the outputs are diode split. However, the other reason for not shorting the outputs with the VSR is because this would alter the voltage on the sense wire, so my modification to the VSR is still valid.
Click to expand...

What difference will it make to the sense voltage ?

Brian
 
halcyon said:
What difference will it make to the sense voltage?
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The shore power charger sense wire is combined with one of the charge wires and is meant to monitor the domestic bank only. Shorting the battery banks together with the VSR would affect the voltage on the sense wire if the batteries were at a different state of charge (which they usually are), or different types (which they are).

This can't be helped when the alternator is doing the charging, although the domestic battery has a separate sense wire connected directly to it from the regulator. Note that these sense wires are nothing to do with the sense circuit in the VSR, which is a much coarser control.
 
I had the same qualms when I fitted a dual-sensing VSR as the Dolphin charger has a separate output for each battery and these would effectively be joined together through the VSR when on shorepower. I contacted the makers of the charger and they said there would be no problem and in fact there doesn't appear to be.
 
JimC said:
I contacted the makers of the charger and they said there would be no problem and in fact there doesn't appear to be.
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There is no problem, it will of course work OK. But that doesn't make it the right thing to do; there is a strong possibility that it could lead to overcharging. My batteries cost over £1000, so I want to be as kind to them as possible. A £1 relay in the VSR ground connection was all that was needed.
 
nigelmercier said:
There is no problem, it will of course work OK. But that doesn't make it the right thing to do; there is a strong possibility that it could lead to overcharging. My batteries cost over £1000, so I want to be as kind to them as possible. A £1 relay in the VSR ground connection was all that was needed.
Click to expand...

If you have a dual output charger sensing only one battery presumably this will be the house battery. This will, I guess, be the larger of the two and usually the one requiring the greater amount of charging.

Does this not mean that the charger will be still charging this battery in the absorption phase of its charging sequence long after the, presumably, smaller starter battery is fully charged and should have been dropped to a float charge .

I was hoping you really had found a dual output charger that would independently charge two batteries according to their individual needs.
 
nigelmercier said:
The shore power charger sense wire is combined with one of the charge wires and is meant to monitor the domestic bank only. Shorting the battery banks together with the VSR would affect the voltage on the sense wire if the batteries were at a different state of charge (which they usually are), or different types (which they are).
.
Click to expand...

Have you considered that the mains charger has one controller feeding to differing battery via two diodes, with sensing from the domestic bank only.

A diode volt drop varies with current passed through it, even a Schottky on low current has a lower forward volt drop. So if your charger is on high current high voltage, it has max volt drop which is compensated for by the controller via your sense wire. But as the engine battery is smaller, and at a higher start capacity, the current it takes will fall quite quickly to a low level. As the volt drop across the diode falls, the voltage seen by the battery increases, could be 0.1 - 0.5 volt higher than the charger, some people refer to it as force feed charge.

With the VSR the engine battery is always no higher than the domestic bank.


Brian
 
VicS said:
Does this not mean that the charger will be still charging this battery in the absorption phase of its charging sequence long after the, presumably, smaller starter battery is fully charged and should have been dropped to a float charge ...
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Quite possibly, but the starter battery was £60, not £1000! Bear in mind that this charger does not need or expect a VSR to be fitted, all I have done is maintained the status quo.

I guess that one could install two chargers, a cheaper low current one for the starter battery, and a smart one for the domestic. [Later] Thinking about it, this may be a cheap way to have more current available for the domestic.
 
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