Chargers and Split Diodes

[welkman]

Having the same issue at the moment re wiring my SHE 27. I have two 110ah batteries and a 1 -2 - both type switch, which I have been told can be dangerous. My new engine has a 70amp altenator and im a bit confused about the options to put in place of a selector switch!

I also have a 10w solar panel currently directly attattched to the lesuire battery.

Diodes - voltage drop
VSR - more expensive (not too sure of the operation) but no voltage drop.

I assume I will still need a ON/OFF switch for both batteries ?

Would you advise putting a third smaller battery in just for engine starting?

Thanks

James

 

[andythilo]

The VSR I bought is actually very good value when you consider the cost of split diodes and disconnect switches. If you go to the link and have a look at the documentation it will tell you everything you need to know.

You should not connect a solar panel straight to a battery, as although they produce very little power, they are the wrong voltage, you should put a solar controller in between, check out the Solsum range, this would be fine for example :

http://cgi.ebay.co.uk/STECA-SOLSUM-...ONTROLLER_W0QQitemZ150372720623QQcmdZViewItem

 

[davidwf]

I always favour the FET type diode splitter to a VSR , no moving parts and very low voltage drop see http://www.es-store.co.uk/category-106.html

I admit they are expensive compared to a VSR though.

 

[Tranona]

Would you advise putting a third smaller battery in just for engine starting?

Thanks

James

As already advised, the BEP marine cluster does the job of both splitting charge and switching. Whether you have a separate starter such as a Red Flash or Odyssey depends on whether you need 220 service capacity.

With low power solar panels check whether you need a regulator. My 6.5w one does not on a 105AH servicse battery.

 

[VicS]

With low power solar panels check whether you need a regulator

A rule of thumb is that if the ratio of solar panel power to battery capacity is no more than 1:10 you don't need a regulator. So 5 watts into 50 Ah is OK etc. BUT it is usually recommended that all solar panels over 10watt are used with a regulator.

 

[William_H]

You should not connect a solar panel straight to a battery, as although they produce very little power, they are the wrong voltage, you should put a solar controller in between, check out the Solsum range, this would be fine for example :

http://cgi.ebay.co.uk/STECA-SOLSUM-...ONTROLLER_W0QQitemZ150372720623QQcmdZViewItem

The concept of a solar panel being the wrong voltage is a bit complex but in practice not correct.

A typical solar panel will develop nearly 20 volts no load or at small current. The solar panel however has internal resistance. Not an actual resistor but a demonstrated resistance. A 10 watt panel has an effective internal resistance of about 40 ohms. What that means is that if you put a short circuit across the output of a 10W panel it will produce .5 amp but of course the voltage will be zero at the output terminals. This will not harm the panel. If you connect a 10w panel to a battery whose static voltage is 12v then .5 amp will flow into the battery. the battery voltage will slowly rise slightly above 12v and the voltage of the panel terminals will read 12v being essentially the same connection. The 8 volt difference is lost or dissipated in the panel itself.
Interestingly as the battery voltage rises to 14+ volts the solar panel will still push in nearly all of the original .5 amps because the internal voltage is still 20v. It means that the battery will be charged at the max rate ie the capability of the panel.up to and beyond overcharged.

The theory is that at small currents ie .5 amp into a 50AH or more battery will not harm the battery over a long period of overcharge. But if the panel is 100w pushing 5 amps into a 50AH battery it will boil the electrolyte and damage the battery with overheating.
The solution to this is to fit a regulator which limits the panel voltage to 14v. This means that as the inherent voltage of the battery rises to 14v (fully charged) the current going into the battery will taper off in exactly the same way your car or boat alternator regulator works. The problem is that in the process of tapering off the current into the battery the final charge takes a long time (is barely achievable) Hence the smart charger (3 stage) style of regulator has advantages.

The solar panel without regulation will not taper off current so gives max charge possible for the size of the panel.
You will actually get more AH out of the solar panel without a regulator than with one. But of course with a large panel you can cook the batteries.

The reason you are perhaps confused about solar being the "wrong "voltage is that by comparison a lead acid battery has a large current capability or a low internal resistance. This means that if you connect say a 24 volt lead acid battery to a 12v lamp it will destroy the lamp. This is because the current flowing in the lamp will be 4 times as much as it should. The battery in most cases will easily supply the 4 times as much current. Of course if the lamp were 12v at 10000watts (10Kw) the current to destroy it would be over 1000 amps. The battery may not be able to supply 1000amps so because of internal resistance of the battery the voltage will fall from 24v to perhaps less than 12v so the lamp will be OK. The battery however may be destroyed by heat dissipation of the internal resistance. ie 1000amps losing 12v inside the battery is 12000w (12Kw) of internal heat.

Another example is a friend connected a tiny 12v 3watt fan to a 20w solar panel. The voltage at the panel terminals (and the fan) remained near 20v at the relatively low current so the fan in fact carried near 1 amp and so was destroyed.It was correct to say in this case the solar panel voltage was too high. Wheras if it were a 20w fan it would have worked well.

This concept of matching internal resistance (or impedance) to get max power transfer follows through into amplifiers and speakers and many other areas of electrics.

On a different subject but brought up by this thread. Welman said he didn't understand a VSR.

A VSR is a relay. ie a switch operated by a small current. It connects your service battery to the engine battery for charging purposes.You can do the same with a switch but you have to remember to connect the switch on starting engine and isolate on stopping engine.

The VSR has a sensing circuit which detects when the engine battery is being charged and reaches about 13v it then connects the service battery so it gets charged as well. When the engine stops the engine battery (now connected to the service battery) voltage falls below 13v so the VSR disconnects.
The actual voltage can be adjusted to be more like 13.5 volts so giving the engine battery more boost before the service battery is connected.(or slightly less)

The sensing circuit can easily be made to sense a rise in voltage of either battery " dual sensing" So relay connects batteries together regardless if the engine or service battery is being charged.

The actual relay can be made very robust so that it can be operated by a separate switch to provide battery paralleling for emergency engine start on both batteries.

While quite reliable the relay has a switch contact which carries all the services charge current so may be regarded as less reliable than a diode. However the diode will waste a lot more power. ie about 1volt at say 20 amp charge is 20w of heating of the diode wasted.

Lesson endeth olewill

 

[Vamoose]

Ooh, I've got one of those!

So have I..It does what it says on the tin !

 

[trying]

Powerstore / Chargers

I am having charger woes.

I bought a sinergex charger from powerstore.

The first one died and the one that replaced it is back with them now!!!!!

So at present i couldn't recommend them or that make of charger...

I hope that they will resolve the issue and it'll be third time lucky fingers crossed...

 

[welkman]

Thanks for the information, it has really helped get my head round the rewiring! Think I will go for the VSR with the battery switches as posted above!

regards

James