Battery Isolator(blocking diode)

[cjepearson]

Good day, Could anyone offer any advice on fitting a blocking diode to my very simple system. I have two batteries(102AH and 75AH) charged from a single alternator through a heavy duty switch(4 position, Off,#1,Both and #2). |Is there any great benefit to fitting a battery isolator, assuming I remember to use the switch properly, and not cook the alternator.
If I should fit one is there anything to look out for, and which one gets the vote. Thanks

 

[halcyon]

The only effect from fitting blocking diodes is to cut your charge level by upto 50%, thus you will have to then fit a alternator regulator to overcome the volt drop, so your simple system is heading for £200 bill.
Live we what you have, it should work ok, assuming it's a modern switch, and save your money.
If you want to go auto look at bi-direction voltage controlled relay, allows either battery to be charged, while the engine can be run from either battery, and a solar panel charge both batteries.


Brian

 

[snowleopard]

The benefit of a splitting diode is that it automatically charges both batteries without you having to do anything. Because it causes a voltage drop you will need to add a smart regulator that senses the battery voltage and makes up for the lost volts. A smart charger will put more amp hours into a battery than the one built into the alternator but it will cost you a bundle.

If you decide to stick with your current setup, use a voltmeter to tell you which battery needs charging.

 

[boatmike]

I recognise that there is a voltage drop with split charge relays that has in the past been significant. To say it has been 50% is an exaggeration however and the modern alternative to them is the battery sensed diode that does exactly the same job with an insignificant voltage drop. The smart regulator, which is often fitted to the charging system overcomes any voltage drop experienced but is not necessary with a good quality blocking diode. If the choice is made to fit a diode without a smart regulator the voltage seen at the battery will drop from a maximum of 14.4 volts on a discharged battery to approximately 13.8 volts which is still well in excess of requirements.
To answer your question, with a blocking diode you don't need to monitor the battery conditions and switch over manually to charge one , two ,or both. It will reduce your voltage slightly but not significantly. Either way you should have a voltmeter fitted to monitor the state of charge of your batteries.

 

[steve28]

Well as the topic is getting a bit interesting i will add the suggestion of a split charge relay, lets see what the others say.....

steve

 

[cindersailor]

I have the same system as your current one and am happy with the way it opperates and do not want to add to the complexity by adding blocking diodes, smart regulators etc. However I was concerned with the possibility of switching to the off position by accident with the engine running and burning out the diodes. In fact I did this momentarily once without any apparent damage, the voltmeter went off the scale though! I therefore plan to modify my switch to provide a physical device which will need to be intentionally moved to allow the switch to be turned to (or from) the off position. A spring loaded button of some sort which could be depressed to allow the switch to pass over it would be ideal, but I have not worked out how to incorporate it into the switch yet. I don't know why such a system is not incorporated into these switches given the well known problem.

 

[halcyon]

When has 13.8 volt been well in excess of requirement,?
A normal diode will drop around 1 - 1.2 volt, which optimistically is 50% battery capacity. Using Schottky diodes you drop this to 0.5 - 0.7 volt drop, this still drop recharge level by around 30% of capacity.
A relay drops around 0.04 volt, cost no more than low loss blocking diodes and gives more charge. Added to that, a solar panel / wind generater can charge both banks.

Brian

 

[boatmike]

Split charge RELAYS are old fashioned. I don't even know where you would buy one now. Be careful as a lot of people call diode blockers SCRs and they are not. The generic term should really be Multi-Battery Charge Isolators. Th best quality ones I have found are made by Sure Power Industries Inc Oregon USA and are stocked by ASAP supplies and others. These are diode based not relays. There are some pretty awful Chinese ones about. avoid these like the plague.

 

[Phoenix of Hamble]

My setup is interesting in this respect in that all three batteries (starter, service and standby) are permanently connected to the alternator via a modern low voltage drop splitter (in fact the Sure Power one mentioned by BoatMike above)... I then have a switch (1, Both, 2, Off) that determines what batteries are connected to the service distribution panel, and a series of isolator keys that allow various combinations of batteries to be connected/disconnected....

Sounds complicated, but it means that I can have three batteries and run services or engine start off any combination of any of them, yet can never accidentally disconnect them from the alternator and thus destroy the diodes.....

It does however take a while to work it out... the default switch position for an engine start is in the OFF position!...

 

[boatmike]

If you are going to argue for the sake of it speak plain English and dont wriggle out by trying to blind everyone with science. You said FITTING BLOCKING DIODES WILL CUT YOUR CHARGE LEVEL BY UP TO 50% . Most people would read that as cutting the either the amperage or the voltage by up to 50% Neither is true.
You also said you will then HAVE to fit a smart regulator. NO YOU WONT. The system will still charge quite happily at 13.8 volts but not as well as 14.4

 

[boatmike]

Actually my own system is somewhat similar with imputs from 2 alternators, 2 solar panels, shore power battery charger and a wind generator to 3 battery banks. I actually have 2 sure power multi-battery isolators rather than one double generator one. With Stirling smart chargers on both engine alternators and a sterling battery monitor I can monitor charge and discharge switch how I like but have had to write myself a manual on the electrical cabinet door to tel me which switch to put in which position to get the desired result cos I am apt to forget.....

 

[Phoenix of Hamble]

LOL..... I have been looking at monitors today for the same reason.....

I also have a wind generator, an Aerogen4, and 2 solar panels directly connected to the batteries....

I also have a complete wiring diagram fastened near the switch... which I consult before moving the battery switch and isolators.....

 

[Chris_Robb]

Mike - I think you are being unfair to Brian - a battery charging to only 13.8V can never acheive much more than 70% of maximum charge. I wish some charter companies would reconise this and fit decent charge regimes, so that I caould actually run the fridge all day and all night!

The drop in voltage really is very significant to the time in which you can acheive a full charge. So he is probably quite right in saying 50% drop - ie you will have to charge for absolutely ages, AND at 13.8V you CAN never acheive the same charge in the battery.

 

[tome]

Agree - the 50% mentioned is probably a very fair estimate. I would fit a blocking diode in preference to a relay, but would arrange the regulator sense downstream of the diode.

 

[bluedragon]

Diodes have a voltage drop, relays don't (better). That's why I fitted a voltage sensing relay this year to my simple two battery system. It's adjustable, bi-directional and seems to do the job well. They are available from a number of sources and don't cost much. But if your switch system works OK, then stick with it.

 

[boatmike]

I am not trying to argue for the sake of it and feel the problem here is that people give instant opinions rather than considered advice. None of us know what kit the guy is running from his batteries or if he has a fridge or not. The original post asked should I fit a battery isolator (split charge diode) or not.
The facts here are simple
Many boats have them fitted and work OK. THe advantage is that there is no need to worry about which battery is being charged. The disadvantage is that it drops thje voltage somewhat. How much? 30%? 50%? % of what?
The normally accepted range of charging for a "non smart" system in either a vehicle or a boat is between 13.8 and 14.1 volts Above that range gassing will occur. Below that the rate of charge is unacceptable.
If you want to charge the batteries more fully fit a smart regulator. Of course it costs money but you don't get owt for nowt. Without a smart regulator witrh just a "normal" charge the best he will get is 14.1 volts. This will drop to 13.8 with a diode fitted. No argument.

 

[cjepearson]

Many thanks for all the replies to my query. I do try to run a very simple boat(Jaguar 27) which does not mean a fridge,windless, or anything else which consumes vast amounts of power. It also means I only motor about 10 minutes into open water on the Blackwater, so charging is minimal. Maybe I should go back to my day sailing catamaran, life was much more simple in those days. /forums/images/graemlins/smile.gif

 

[bluedragon]

Actually, what nobody has asked you is whether your alternator and its regulator is machine or battery sensed? If the former (or you don't know), then avoid diodes and stick with switches or relays. Most diode installations are with battery sensed regulators I believe (compensates for the voltage drop).

 

[halcyon]

I'm not going to carry on, it's a waste of time, but if you read my reply at the top, I said do not fit a blocking diode, it will not do any good, stay with your switch. If you want a automatic system use a voltage controlled relay.
Which was a simple bit of advise that I have given out for over 25 years to boat builders and owners alike.


Brian

 

[Stemar]

I use a simple relay - a suitable one's £5 from Maplin - energised from the charge warning light terminal on the alternator to switch my domestic battery into the charging circuit. It's simple, cheap and it works.

I've heard I may lose a bit of battery life. I'm not convinced, but if I have to buy an extra battery in 5 years, I can afford that from what I've saved on the Adverc or Stirling regulators.

If you're interested in a circuit diagram, PM me