Voltage sensitive relay unusal question (probably)

[tim_ber]

Still a novice, but enjoy tinkering with electronincs.

Wish to use my old lead acid batteries that are too poor to crank engines, but good enough to use in the garden to light things.

Currently one 5W solar panel keeps an old battery up to 12.7 volts with ease.

Can anyone point me in direction (I have googled and failed) for instructions on how to make one's own vsr for getting the solar panel to charge a second battery when #1 is at a good enough Voltage ( can't wire batteries in parallel of course).

Is it even possible to make one's own vsr? Bearing in mind I only learn what I need to learn, e.g. I have learned a lot about LEDS from you guys, but the other 99.999...% of electronics is still a mystery to me probably.

I'm not stupid or thick - some may say stupid for trying, but I like tinkering and I do a good job in the end. (Re-wired my house and got it signed off with a pat on the back for a good job)
Thanks in advance. Helping a mate launch his boat tomorrow - he is as nervous as a cat, I remember when I used to be like that.

 

[AndyJ76]

If you want to build your own circuit, then look at something to do with voltage sensing and then use the output to switch a relay.
You'd probably want to do something with a voltage divider and a zener diode.

I'd probably just buy the VSR. I bought one of these http://www.ebay.co.uk/itm/0-727-33-...TAGE-SENSITIVE-INTELLIGENT-RELAY/121110586358
It does dual sensing, even though it doesn't say so. (I have wind and solar to domestic, and alternators to the engine start banks, and it opens whenever either bank exceeds 13.2V)

 

[halcyon]

Still a novice, but enjoy tinkering with electronincs.

Wish to use my old lead acid batteries that are too poor to crank engines, but good enough to use in the garden to light things.

Currently one 5W solar panel keeps an old battery up to 12.7 volts with ease.

Can anyone point me in direction (I have googled and failed) for instructions on how to make one's own vsr for getting the solar panel to charge a second battery when #1 is at a good enough Voltage ( can't wire batteries in parallel of course).

Is it even possible to make one's own vsr? Bearing in mind I only learn what I need to learn, e.g. I have learned a lot about LEDS from you guys, but the other 99.999...% of electronics is still a mystery to me probably.

I'm not stupid or thick - some may say stupid for trying, but I like tinkering and I do a good job in the end. (Re-wired my house and got it signed off with a pat on the back for a good job)
Thanks in advance. Helping a mate launch his boat tomorrow - he is as nervous as a cat, I remember when I used to be like that.

Simple to do, take a small latching change-over relay, wire common to solar panel, one set of contacts to each battery. When voltage gets to a preset level it flips over to battery 2 and puts it on charge. When battery 2 reaches preset value it flips the relay back to original state and charges battery 1 again.

You cannot use a VSR as your charge source power is to low, though a pair of MOSFET's could be a alternative in place of relay if your feel daring.

All need you need now is the circuit design.

Brian

 

[maxi77]

I have used these few times with no problems

http://www.ebay.co.uk/itm/SPLIT-CHA...ervan_Caravan_Accessories&hash=item5657775cc9

 

[Rigger Mortice]

Here's something to start with. http://www.zen22142.zen.co.uk/Circuits/Switching/vcs555.htm

 

[nigelmercier]

Why can't you parallel them? They will charge just as quickly.

A VSR is only used when the batteries must be separate, as in start and domestic. And there is a common misconception that they somehow sense that one battery is charged, and switch to the other bank. They do not, they just sense that there is a charging voltage, and parallel the batteries.

 

[tim_ber]

Why can't you parallel them? They will charge just as quickly.

A VSR is only used when the batteries must be separate, as in start and domestic. And there is a common misconception that they somehow sense that one battery is charged, and switch to the other bank. They do not, they just sense that there is a charging voltage, and parallel the batteries.

I thought (and of course could be wrong as if more often the case than not) that a poor battery in parallel with a better battery will adversely affect the better battery. Of course the batteries I will be using (maybe up to 4 or 5 of them - yup, garden will look great) will be off highly dubious quality and certainly not matched sets.

 

[tim_ber]

Here's something to start with. http://www.zen22142.zen.co.uk/Circuits/Switching/vcs555.htm

Great. Thanks for that.
Cool little circuit that. Only 200mA but very interesting, thanks.

 

[tim_ber]

I have used these few times with no problems

http://www.ebay.co.uk/itm/SPLIT-CHA...ervan_Caravan_Accessories&hash=item5657775cc9

Thanks for that. I will read more carefully in a moment to ensure it is not a split charge system (that I read on here has a large voltage drop) as opposed to VSR. Thanks for link.

 

[tim_ber]

Simple to do, take a small latching change-over relay, wire common to solar panel, one set of contacts to each battery. When voltage gets to a preset level it flips over to battery 2 and puts it on charge. When battery 2 reaches preset value it flips the relay back to original state and charges battery 1 again.

You cannot use a VSR as your charge source power is to low, though a pair of MOSFET's could be a alternative in place of relay if your feel daring.

All need you need now is the circuit design.

Brian

What makes the relay 'know' when to flip over though.
Will click on your website and have a looksee thanks

 

[tim_ber]

Why can't you parallel them? They will charge just as quickly.

A VSR is only used when the batteries must be separate, as in start and domestic. And there is a common misconception that they somehow sense that one battery is charged, and switch to the other bank. They do not, they just sense that there is a charging voltage, and parallel the batteries.

Just read the "And there is a common misconception that they somehow sense that one battery is charged, and switch to the other bank. They do not, they just sense that there is a charging voltage, and parallel the batteries."
I was under that misconception clearly.

So, would a domestic battery (that is not leisure but simple lead acid and been poorly treated and discharged to 11V say and is therefore not as healthy as the cranking battery that has been charged at 14V from alternator and so forth) not 'pull' the healthy cranking battery 'down' when the VSR kicked in and set the 2 batts in parallel?

 

[DaveS]

Still a novice, but enjoy tinkering with electronincs.

Wish to use my old lead acid batteries that are too poor to crank engines, but good enough to use in the garden to light things.

Currently one 5W solar panel keeps an old battery up to 12.7 volts with ease.

Can anyone point me in direction (I have googled and failed) for instructions on how to make one's own vsr for getting the solar panel to charge a second battery when #1 is at a good enough Voltage ( can't wire batteries in parallel of course).

Is it even possible to make one's own vsr? Bearing in mind I only learn what I need to learn, e.g. I have learned a lot about LEDS from you guys, but the other 99.999...% of electronics is still a mystery to me probably.

I'm not stupid or thick - some may say stupid for trying, but I like tinkering and I do a good job in the end. (Re-wired my house and got it signed off with a pat on the back for a good job)
Thanks in advance. Helping a mate launch his boat tomorrow - he is as nervous as a cat, I remember when I used to be like that.

Look up comparators. Basically you want to compare a variable voltage (your first battery) with a fixed reference voltage at which you want to parallel up your second battery - because that's what a VSR would normally be arranged to do. Normally a comparator circuit would be made using an operational amplifier (circuits from e.g. RS or elsewhere on line). The reference voltage can be obtained in a number of ways: a high value resister feeding a diode chain is probably simplest, with a small trim potentiometer across the top diode, but do also check zener diodes. To avoid power supply issues and to be able to feed everything from one of the batteries it might be best to set your reference voltage to half the desired actual value, use a 2 equal resistor chain to give half the measured voltage, and carry out the comparison on the two halved values. The output of the comparator would, via a transistor (possibly a Darlington) drive a relay capable of switching the charging current. Look up snubber diodes and use one to protect the transistor from back emf.

Clarification here: most commercial VSRs close at around 13.4V or so: if you're only getting to 12.7V while charging then you aren't fully charging the battery. Alternatively if 12.7V is the rest voltage then a switching voltage of somewhere above 13.2V and below the charging voltage when full would be fine. If you really meant that you never want to parallel the batteries, but to transfer charging to the second battery when the first one is full then that could be arranged using a change-over relay, but you would need to set the switching voltage higher, to 14.4V or whatever you get when the on charge battery is full.

Commercial VSRs generally have built in hysteresis, i.e. they open their contactor at a lower voltage than it closes, maybe 12.8V, to avoid the relay chattering when the second battery is paralleled. If you want to use the change-over system rather than paralleling you won't need this feature. If you do decide to parallel the batteries then hysteresis can be achieved in a number of ways, perhaps the simplest being to use a second switch in the relay to alter the chain of components providing the reference voltage by shorting out a diode or resister.

Of course you could do it with a micro controller instead, and some on here would no doubt so advise... In all seriousness, if you wanted to make your system more sophisticated, by say alternating on a daily basis which battery should be charged first, or extending it charge multiple batteries in turn (which you suggest may become available) then programming would be the way to go, but as described I think an analogue circuit would be cheaper and perfectly adequate.

 

[nigelmercier]

So, would a domestic battery (that is not leisure but simple lead acid and been poorly treated and discharged to 11V say and is therefore not as healthy as the cranking battery that has been charged at 14V from alternator and so forth) not 'pull' the healthy cranking battery 'down' when the VSR kicked in and set the 2 batts in parallel?

Yes. But the converse is true, the good battery will pull up the bad one. If the voltage drops below the hysteresis point of the VSR, it will drop out.

However, we don't care about any of this, we are charging.

 

[halcyon]

Why can't you parallel them? They will charge just as quickly.

A VSR is only used when the batteries must be separate, as in start and domestic. And there is a common misconception that they somehow sense that one battery is charged, and switch to the other bank. They do not, they just sense that there is a charging voltage, and parallel the batteries.

To a large degree they do.

The VSR works on the fact a battery has three operating voltage ranges, no load, discharge and charge. The engine battery is charged up to a voltage, and the relay closed, the service battery is normally discharged in comparison to the engine battery. The alternator output takes the line of least resistance, the service battery, and the voltage will fall. This is to low to charge the engine battery, but to high to discharge it. The service battery is charged until it's voltage comes up the charge voltage of the engine battery, they then both take a charge, as a large multiple battery bank.

Brian

 

[DaveS]

Great. Thanks for that.
Cool little circuit that. Only 200mA but very interesting, thanks.

But it's the 555 that has the 200mA output limit: in this circuit it's driving a small relay with a coil current hopefully well below that. The relay switch contacts would handle your c. 400mA charging current.

 

[tim_ber]

Look up comparators. Basically you want to compare a variable voltage (your first battery) with a fixed reference voltage at which you want to parallel up your second battery - because that's what a VSR would normally be arranged to do. Normally a comparator circuit would be made using an operational amplifier (circuits from e.g. RS or elsewhere on line). The reference voltage can be obtained in a number of ways: a high value resister feeding a diode chain is probably simplest, with a small trim potentiometer across the top diode, but do also check zener diodes. To avoid power supply issues and to be able to feed everything from one of the batteries it might be best to set your reference voltage to half the desired actual value, use a 2 equal resistor chain to give half the measured voltage, and carry out the comparison on the two halved values. The output of the comparator would, via a transistor (possibly a Darlington) drive a relay capable of switching the charging current. Look up snubber diodes and use one to protect the transistor from back emf.

Clarification here: most commercial VSRs close at around 13.4V or so: if you're only getting to 12.7V while charging then you aren't fully charging the battery. Alternatively if 12.7V is the rest voltage then a switching voltage of somewhere above 13.2V and below the charging voltage when full would be fine. If you really meant that you never want to parallel the batteries, but to transfer charging to the second battery when the first one is full then that could be arranged using a change-over relay, but you would need to set the switching voltage higher, to 14.4V or whatever you get when the on charge battery is full.

Commercial VSRs generally have built in hysteresis, i.e. they open their contactor at a lower voltage than it closes, maybe 12.8V, to avoid the relay chattering when the second battery is paralleled. If you want to use the change-over system rather than paralleling you won't need this feature. If you do decide to parallel the batteries then hysteresis can be achieved in a number of ways, perhaps the simplest being to use a second switch in the relay to alter the chain of components providing the reference voltage by shorting out a diode or resister.

Of course you could do it with a micro controller instead, and some on here would no doubt so advise... In all seriousness, if you wanted to make your system more sophisticated, by say alternating on a daily basis which battery should be charged first, then programming would be the way to go, but as described I think an analogue circuit would be cheaper and perfectly adequate.

Thanks for that, and thanks Nigel below for clearing up my mis-understanding of parallel business.

That was all great. I can feel synapses firing and stopping the dementia setting in. Another project to get into.
Yes, on a good day, the 5W solar panel will charge the battery in the shed at over 13.7V. Not a tracking solar panel, but at a reasonable angle etc.

Many thanks.
Launch mate's boat tomorrow, 2 days of work and then get my teeth into this interesting stuff. Might buy that £12 ebay thing and make comparisons.

Thanks a lot guys.
Better hit the sack or I'll wake up foggy and forget to take an essential bit of kit to mate's boat; he is seriously lacking a lot of essential stuff - like a toll box for a start!

 

[nigelmercier]

The VSR works on the fact a battery has three operating voltage ranges, no load, discharge and charge...

The battery states you quote are measured at rest, you can't deduce anything from the voltage while charging. If I had an alternator that didn't instantly take my batteries above the switch level of the VSR I would consider it faulty.

 

[halcyon]

What makes the relay 'know' when to flip over though.
Will click on your website and have a looksee thanks

Same type of circuit that runs the VSR, but takes no current to run the relay. Look up flip flop logic circuits, batt 1 charge voltage flips it one way, then batt 2 charge voltage flips it the other way.

A MOSFET in the earth side ( could be a cincideration in power usage ) of each battery, then the flip flop circuit just drives either one into conductance to charge either battery.

Brian

 

[halcyon]

The battery states you quote are measured at rest, you can't deduce anything from the voltage while charging. If I had an alternator that didn't instantly take my batteries above the switch level of the VSR I would consider it faulty.

You consider the charge voltage range every time you put a battery on charge, be it engine, mains, solar or wind. The voltage you see is set by the battery chemistry, the alternator only provides the means.

Brian

 

[William_H]

A simple VSR as described ie using a 741 Op amp as a comparator a 5v zener on one input and a voltage divider from the battery on the other input all driving a relay can be built quite easily. It can work really well. The voltage that you set the VSR to operate at is an interesting question. If you set it to around 13v then it will release if engine battery is not on charge and as soon as or shortly after the alternator fires up your battery voltage will rise above 13v to more around the 13.75 volts or so. ie the engine battery voltage will come up quickly in recovering from the start.
Now when you parallel a service battery much depends on the size of the battery and its charge state. If it is a large flat battery then it will pull down the engine battery/alternator combination in voltage. This pull down of the voltage will cause the VSR to release. The VSR may then operate again cycling continually until the service battery voltage has been lifted by the pulses of charge. This is not very healthy for the VSR relay contacts.
As said a hysteresis ie a difference of operating voltage to release voltage will help except in the case of a really flat big service battery. Even then the longer on time will get the voltage of the service battery up with less cycles. Another way to avert this problem is to introduce some resistance into the charge wire through the relay contact. This will limit the large current going into the flat service battery enabling the alternator to hold the voltage high enough to keep the VSR operated. As the service battery is charged the current will fall so voltage difference becomes minimal.

The actual setting of the pull in voltage of the VSR will determine just how much charge the engine battery gets before the service battery gets a charge. So a VSR set at 13v will pull in almost immediately alternator kicks in. A vsr set at 14v volts will not pull in till engine battery gets to 14v. This voltage will not appear until the engine battery is well on the way to fully charged. This depending on the alternator current capability. The alternator will be trying to provide 14 or more volts and the engine battery will be taking charge so it is still a bit variable just ho well charged the engine battery is before the VSR kicks in.
Not that this really matters as the alternator should be able to charge both batteries. So this idea of second battery only being charged when engine battery is charged is just a bit of salesman hype.

Anyway back to OP question. I would put all batteries in parallel if one is dead ie low in voltage then it is no use to you at all.
A 5 w panel will not give a lot of charge but then it all depends on how many garden lights you run and for how long.
I have nominally 30 w of panels and about 18 watts of LED garden lights. These run on a timer for 5 or 6 hours per night.
I built a little VSR circuit to turn the lights off if the battery voltage falls below 11v. I don't know if it has had reason to operate as I am asleep but think not.
I use batches of sub C NiMh batteries in parallel as the cheapest I think battery power from China. (setting aside old car batteries)
The sub C batteries are claimed to be 6AH ( a lot less by testing) but i have 5 sets of 10 cells. My biggest problem is in summer the batteries get hot from overcharging. I don't believe a regulator would help as the NiMH actually fall in voltage at overcharge so I just disconnect some of the solar panels.
Anyway just a bit of waffle from olewill which may be of interest. good luck... PS do knock up a simple VSR they are kind of fun and useful.