Diode thingy's

[Colin K]

Hello,
I wondered if I could pool from others electrical knowledge ? On my humble boat I have separate 12v and 24v systems which all works very well. Oddly having a great lump of an a 24v alternater and decent 24v battery charger on board I had a problem of charging the 12v circuit. I asked for a bit of advise on here and a regular suggested a 24v to 12v reducer and this has worked great. Thanks. There is just one niggle in that even when I turn off the 24v system but say leave a light on I notice the 12v side feeds back (dim light) and I think think that this is through the reducer ?? I think a diode is an electrical one way valve and wondered if this would fix it ? where best to fit it ? and what size ? (reducer is 6a) And can I get one from Maplins (nice and near to me) Looking at this I notice that I shared all of the negatives whatever the voltage, Have I dropped a clanger doing this ?
Thanks, Colin.

 

[VicS]

Id not have thought that should happen!

What is the " reducer"

The trouble with adding a diode might be the volts drop across it.

I think I would disconnect the "reducer" to confirm that really is the cause before going any further

 

[Rigger Mortice]

It seems odd, but it's hard to say without more information. If the "reducer" is connected to a 12volt battery then it's possible that the 12v is feeding back into the 24volt system. A diode could solve that but, as already stated, you may have problems with voltage drops. But it all depends on the circuitry. It may be that a diode fitted in the 24v supply to the "reducer" will work without voltage drops being a problem.

Why not give us details of the "reducer"?

Yes, Maplins stock a reasonable range of diodes.

 

[Colin K]

Hello chaps thanks for this so far. Its an old vitronics unit inherrited with the boat to do just what it was supposed to do and provide 12v off a 24v system to satisfy the growing trend of 12v stuff. It does the job and has done for 2 yrs nicely ta. It was Vic who said give it a go in the oposite direction. np.
This feeding back is no great problem just worried that the 12v side could be flattened if i ever forget to turn everything off.
All the best, Colin.

 

[pappaecho]

You could of course buy a cheap blocking diode fit it to the circuit and see what happens. At worst case there could be a small voltage drop, when you decide either to live with it, or dump the modification

 

[Colin K]

Thanks, Do I fit this diode in line in the positive feed ?
Thanks, Colin.

 

[Rigger Mortice]

Thanks, Do I fit this diode in line in the positive feed ?
Thanks, Colin.

Yes.
At risk of stating the obvious, just make sure that you get one that can handle that current adequately. I'ld go for something like a 10amp diode.

 

[William_H]

12V reducer

I find all this very confusing. Some mis understanding on someones part.
You have a standard 24v system with a battery switch. This is connected to a 24 to 12v power reducer.
If you turn the 24v supply off the only way you can get a light on the 12v system to glow dimly is if there is a battery on the 12v system. This is of course a common arrangement. However surely you would know if there was a 12v battery in the system? If there was one hidden away it may well be cactus if light is only on dim without the converter powered.

In this arrangement The 12v battery becomes the service battery while the 24v battery remains the engine battery.
The 24 to 12v converter should supply actually 13.75 volts so will nicely charge the 12v battery and supply the load.
You would need to be sure to turn off the 24v supply to the converter when you stop the engine or fit a 24v Voltage sensing relay to the 24v supply so the converter only supplies power when the engine is charging so averting any discharge of the 24v battery.

Assuming there is a 12v battery then I don't think it could discharge back through the converter into the 24vsystem. However you could check this with an amp meter on milliamp range. if it does then indeed a diode could be inserted int he 24v supply. The volt drop will not be of concern (so much) because .7 volt lost in 24v is a much smaller proportion than .7volt in 12v system. In any case the converter will automatically make allowances for any volt drop. (internally regulated to 13.75v output.

Incidentally if you have a 12v battery then for emergency engine start it can be c0onnected in parallel with the 12v battery of the earthy half of the 24v (2X 12v) battery. This will give some boost for starting.
If you went for 2 batteries in the 12v system then a complicated rewire would allow the batteries to be connected in series for engine battery boost.

Now a 12v battery is not necessary for the 24 to 12v converter. Simply connect radios etc to the converter the load being less than 6 amps (the converter rating) and you have no worries. You might need to consider however having a dual 24v battery system (if you havn't got one) to provide protection and then back up for the engine start batteries.
Now what was the problem? good luck olewill

 

[Ubergeekian]

I asked for a bit of advise on here and a regular suggested a 24v to 12v reducer and this has worked great. Thanks. There is just one niggle in that even when I turn off the 24v system but say leave a light on I notice the 12v side feeds back (dim light) and I think think that this is through the reducer ??

Like, I suspect, from the replies, others, I haven't much what you're on about here. Do you mean that you have a 24V system (alternator/starter/battery) which charges a 12V system (including battery), and that a 24V side bulb will glow dimly even when the 24V battery is switched off?

If so, are you sure the 24V battery is off? What happens if you disconnect it? What happens if you disconnect the 12V battery? Have you measured the voltage across the 24V bulb when this is happening? Have you measured the voltage across the terminals if you remove the bulb?

A diode can be used, crudely, as a one-way valve for electrical current, but it's not quite as simple as that. There is a voltage drop across the diode, typically 0.65V - 0.7V, so they can mess up supply or charging voltages and they can dissipate a lot of heat. Other solutions might include a 24V-side sensed relay which disconnects the converter, or mending the converter if it's faulty, or just not worrying about it.

 

[Beyondhelp]

May I suggest perhaps since you're potentially playing with high current, if you are in any way unsure of what's going on to perhaps ask someone to help you locally who does?

You really don't want to make an expensive mistake by accident.

 

[Rigger Mortice]

Looking at this again makes me think that, whilst a diode may "fix" the problem, it's probably not the way to go.

You've got a good quality converter (I assume you meant "Victron"). It's not a cheapie, so it's unlikely that any stray voltage is being fed back through that. So you need to find out what the cause is.

If you have a meter it may be an idea to take some readings with the different batteries connected and disconnected and that may give you a clue.

I'm wondering if you have added something in the 12 volt circuit and inadvertently connected it to the 24 volt circuit? Otherwise check for poor, loose, dirty connections somewhere on the boat. Check also that the main switch really is switching off.

Of course, it is possible that the converter is faulty.

To be frank, I would try to find out what is wrong. At best it may just be inefficient, at worse it could lead to a fire. I'm inclined to think that using a diode is simply a botch; a bit like putting a bucket under a leak and saying "Fixed it".

But, I would start by checking that anything I had added was done so correctly.

 

[Colin K]

Hello chaps thanks for the replies. I will try my best to advise of the boats electrical set up to see if it helps.

I have 2 24v battery banks both are 2 12v batteries in the way that you wire them to get 24v !!! and one 12v circuit that is 2 12v batteries wired in the way you get 12 v !!! Sorry for the vague Parralel / Series explanation.
I know how to do it in practice.

The engine is a Watermota Sea Panther which works at 24v has a massive 24v alternator and so what ever possible i run as much as possible at 24v as I have always been informed that it draws 1/2 the amps. So the waeco the radar, The Eberspacher, ie the big drawers are 24v. (I have a younger wife and 11 yr old girl so there domestic needs are large ha ha.

The 12v system is for those nav equiptment etc that has to work at 12v.

Just typing this of course is making me think where on earth have I connected the 12/24v reducer in and as many of you have said I must disconnect the reducer to make sure the 24v lights still work be it dimmly with the 12v disconnected. The 24v system has an isolator switch as well as a 1, 2, both set up.

On the boat all next weekend in the lovely Ipswich Haven marina where we have just moved so I will be active with the meter.

Once again thanks chaps. Colin.

 

[Beyondhelp]

Just a thought but I guess other than for backup (eg the 24>12v converter failing) having the 12v batteries may not be necessary at all, unless you have any large 12v current devices. Most 24>12V DC-DC converters are nice and efficient and having all batteries at 24v may perhaps be a better idea?

No need to worry about stray currents etc doing things you don't expect then.

 

[Rigger Mortice]

Just another thought. Beyondhelp is right but, if you must have batteries in the 12volt circuit, it seems unnecesary to have 2 of them. You are charging with a maximum of only6 amps. It's probably going to be inefficient to take 24volts from one battery, reduce it, store it in another battery, then draw it off to your 12 volt circuit.
It all depends on what equipment you are running at 12 volts.

It might also be worth checking what the converter is churning out. If it is producing just 12 volts then that is not enough to charge the batteries properly. You would expect it to be producing something like 13.8 volts if it was intended to charge batteries.

Looking at the Victron site they make different converters. Some produce 12 volts (direct supply, no battery) some 13.8 volts (for battery charging)

 

[Colin K]

My goodness chaps you have a good point. Historically I had a 12v Eberspacher and so a 12v bank was necessary. Just last week the D1 came out and I fitted a 24v D5 so my 12v needs are the Tiller pilot, Fishfinder,2 GPS's and 2 12v car sockets that power a dvd for junior and phone chargers.
Excuse my ignorance just out of curiosity what does a diode look like ?
Thanks, Colin.

 

[VicS]

A though struck me !

Is your 24 to 12 volt converter intended as a power supply only, ie not as a battery charger or is it truly a 24 to 12 volt battery charger.

Victron make both types!

If the former it wont effectively charge the 12 volt battery and since it is not designed to have 12 volt battery connected what you see may be the result of doing that.

If it is a 24-12 volt battery charger then I think before doing anything else you should disconnect it to proves that its the cause of the trouble.

Diodes come in many shapes and sizes. The basic is just a wire ended component marked in some way ( a silver band ** perhaps ) to show which connection is the cathode.

** not the type with trumpets and things.

 

[Barry Jones]

Personally, I would just have a 24V battery system charging from your 24V alternator.

If you have an existing Vtronix 24-12V power supply and its big enough, run your 12V items off the power supply.

Failing that, fit a larger one - they aren't expensive - I wouldn't use Victron for this - too expensive.

My goodness chaps you have a good point. Historically I had a 12v Eberspacher and so a 12v bank was necessary. Just last week the D1 came out and I fitted a 24v D5 so my 12v needs are the Tiller pilot, Fishfinder,2 GPS's and 2 12v car sockets that power a dvd for junior and phone chargers.
Excuse my ignorance just out of curiosity what does a diode look like ?
Thanks, Colin.

 

[Beyondhelp]

by the sounds of it, this would do all you need:

http://www.caravantechnology.com//24V-to-12V-DC-DC-Converter-P23.aspx

12v @ 17A cont.

Could even buy a second for backup they are so cheap! Then swap the other two 12v onto the 24v bank and then you have a much more simple and easy to isolate system!