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Old 20 February 2008, 19:49   #21
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The best isolators I've found so far have been these:-


They are used on HGV tail lifts so are designed to be used outside.The keys are non-removable. They can be completely sealed by the judicious application of sikaflex round the base and an o-ring under the turn key.

I completely submerged the one on my sr4 3 times while it was turned on and apparently it's still working now-18 months later.
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Old 21 February 2008, 02:58   #22
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Quote:
Originally Posted by jwalker View Post
Much like the second one but I used a switch in the negative line. I did this because negative isolators are available which are in the form of a negative battery terminal which is 'jumped' by tightening a thumb screw. This made it very easy and the diode can have an 8mm terminal on each end which is simply put behind the clamp bolt nuts.

Here's one.

The end with the bolt through it is a taper which your standard battery cable fits onto. I'm sure you could adapt that fuse holder to house the diode to make it a neat solution.
Jeff,

Firstly excuse my ignorance on this subject,but purely as a laymans observation, that type of connection "appears" to make or break the flow in a way that might cause a spark, am I correct ?, if so the proximity of my battery to the fuel system in the consol (which I've always thought a little suspect) may make it dangerous....just a thought as a lot of ribs seem constructed in this fashion..
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Old 21 February 2008, 05:09   #23
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I guess that's a possibility but it's generally the case for switches too. However, if you're living with a consol full of explosive vapour, hydrogen or fuel, you need to do something about it.

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Old 21 February 2008, 16:53   #24
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Nonsense. We've had this conversation before.
Your notion of a battery never reaching full charge is not correct and it presumes the battery with the diode is initially fitted in a partially discharged state. Fitting a fully charged battery and then using a diode to preserve the charge works fine. Even if you accept the voltage drop as 0.7v (which it usually isn't) you'll still have a charging voltage of approx 13.7v which is just fine for a float charge. If you're wise, you'll choose to use a schottky diode which has a voltage drop of approx 0.4v.
If you end up with a really difficult situation and you've partially discharged your backup battery too, all you need to do is ensure your switch is in the correct position to recharge it fully.

All these suggestions of switching....what a hassle.

I use a diode with complete success. Both my batteries are now over 4 years old and still work fine and they are starting a big diesel engine not a little outboard motor so I guess they're still delivering satisfactory current.

I have a 1-both-2 switch but I never switch it, it's always on both but I also have an isolating switch for the battery with the diode so it's the equivalent of always being on 1. During my boat build I felt it may be useful to have the switching facility but I've never used it. Some folk say it gives safety but I feel it's very little - after all, do you disconnect your car battery each time you park?

I think that is the way to go. Personally, I'd use two simple single switches; one as a main switch and one in series with the negative connection of the backup battery with the diode wired across it. Dead simple, no switching necessary in normal use and both batteries remain charged.
jwalker,

This (usefullness of diodes) is not "nonsense" as you so kindly put it!

I do agree that a charge diode will maintain an already charged batt in float stage but you mentioned you never used the link switch so is your 2nd batt fully charged? . If the 2nd batt is never connected to anything other than the charger (ie it's a complete standalone backup batt) then this approach is probably ok but imost dual batt installs would have dedicated engine start on 1 batt and house electrics on the other. In this case the switch will need to be regularly moved. A charge relay provides a better solution that a diode in this case (see below) - but link switch is still needed. Float state is also only valid if the battery is 100% charged (ie it's the idle state after going through a full charge cycle)


Re charge diodes:

In a typical split battery installation, one batt will be used for engine start and one will be used for domestic electronics. If the one linked to the main charge system via diode (I'll call it batt 2) is flattened to any real degree, it will not charge properly with just a diode.

In your example, float charging at best case 14v will not charge the 2nd batt to 100% (never reaches absorption stage so capacity is minimised and sulphination will eventually take place). If this batt is used to start the engine there is a fair chunk of charge taken out and the batt neads charged, not raised to float. It will do some bulk charge but will never complete. If the 2nd battery is used for domestics, again over time this batt will loose capacity.

The other thing to remember is that the alternator will also have to charge the first batt fully to get to 14.4v before the second batt is at max 14 so 2nd batt is already at a disadvantage.

I imagine that in most situations you may not see a huge problem as you generally never use the full capacity of a battery to either start the engine or run electronics with engine off. The fact that your batts have lasted 4 years does not mean they are at 100% capacity. 1st sign of a dead car battery is on a cold winter morning but the same batt will be fine over the summer so a lot depends on load. An 85aH marine batt with 900 cold cranking amps will easily start a 2.0l diesel engine but if it's sulphanated, it will not turn the engine over for long - if your engine starts easily, you would not even notice.

Sure, a charging diode will work but will not work properly - it can't defy physics. If you want fully charged, fully maintained batts, the only way is a physical link between them or a proper split charger.

Another potential issue is that a lot of outboard alternators don't actually produce 14.4V at the batt terminals either (my last 2 have certainly not) so already there is a disadvantage and adding more voltage drops does not help... You are no doubt at an advantage with an inboard that will have a high o/p alternator and probably produces 14.4V

This is not personal opinion, it's well documented by many battery manufacturers, OEM's and charge controller guys alike. Diodes do not provide an optimal soln for charging.
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Old 21 February 2008, 17:06   #25
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Originally Posted by Nos4r2 View Post
The best isolators I've found so far have been these:-


They are used on HGV tail lifts so are designed to be used outside.The keys are non-removable. They can be completely sealed by the judicious application of sikaflex round the base and an o-ring under the turn key.

I completely submerged the one on my sr4 3 times while it was turned on and apparently it's still working now-18 months later.
Yip agreed - had 3 of these on a 3-batt install on a yacht and never had any issues whatsover with them despite them getting regularly doused with salt water. The ones I used (which look identical) seemed to do a combination of 90 degree rotation as well as kind of screwing into the switch body (don't know how else to explain it) but it means there is a very positive contact and not just a wiper motion.

The standard "red removable key" switches do not on the other hand like being immersed
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Old 21 February 2008, 18:35   #26
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Originally Posted by al40 View Post
This is not "nonsense" as you so kindly put it!
Yes it is. You said, "Avoid bloking diodes at all costs." and that is nonsense.

I do understand about the battery charging process and I happen to own a sophisticated, multi-stage charger but we are in the real world and in a typical rib or road vehicle application batteries are not charged to their absolute maximum but they, nevertheless, perform satisfactorily.

Quote:
In a typical split battery installation, one batt will be used for engine start and one will be used for domestic electronics. If the one linked to the main charge system via diode (I'll call it batt 2) is flattened to any real degree, it will not charge properly.
But that's not typical for a rib and Bruce specifically said he wanted the second battery as a backup should the main battery fail or become discharged. It is entirely possible that the backup battery will never be used.

Quote:
In your example, float charging at best case 14v will not charge the 2nd batt to 100% (never reaches absorption stage so capacity is minimised and sulphination will eventually take place).
I didn't say it would. I suggested the batteries should be fitted fully charged and the float charge via the diode would maintain that charge.
Quote:
If this batt is used to start the engine there is a fair chunk of charge taken out and the batt neads charged, not raised to float.
Again, that is not the case I proposed and I said that all that is required is to set the switch to the battery needing to be charged, thus bypassing the diode during the recharge. Given that this is likely to be a nonexistent or limited event, I felt it not to be unreasonable.

Quote:
I imagine that in most situations you may not see a huge problem as you generally never use the full capacity of a battery to either start the engine or run electronics with engine off.
Yep, and that's the cop-out clause I've heard so many times but in reality I've not found it to be the case. I used the diode system also in my previous rib and I owned it long enough for batteries to expire normally and it was always the case that the main battery failed first. I imagine it has a harder life because of it's constant use.
Quote:
The fact that your batts have lasted 4 years does not mean they are at 100% capacity. 1st sign of a dead car battery is on a cold winter morning but the same batt will be fine over the summer so a lot depends on load. An 85aH marine batt with 900 cold cranking amps will easily start a 2.0l diesel engine but if it's sulphanated, it will not turn the engine over for long - if your engine starts easily, you would not even notice.
Firstly, as explained below, they won't have been maintained at 100% capacity anyway. Secondly, my engine isn't a 2lt diesel. Thirdly, they are normal road vehicle batteries not marine ones. Fourthly, I have recently had the necessity of prolonged engine cranking because I needed to prime the oil system to my turbocharger and the battery performed fine so they appear not to hold to your degredation theory either. At least, not yet.


Quote:
Another potential issue is that a lot of outboard alternators don't actually produce 14.4V at the batt terminals either (my last 2 have certainly not) so already there is a disadvantage
Agreed. But vehicle alternator voltage regulators are nominally rated at 13.7 to 14.2volts so they are not capable of driving the battery to maximum charge but that doesn't mean they will not maintain a satisfactory charge and ensure the battery has satisfactory longevity.
Quote:
You are no doubt at an advantage with an inboard that will have a high o/p alternator and probably produces 14.4V
Nope, it's just a glorified road vehicle alternator.

Quote:
This is not personal opinion, it's well documented by many battery manufacturers, OEM's and charge controller guys alike. Diodes do not provide an optimal soln for charging.
I've no quibble with you about the ideal battery charging regime but this is not typical of vehicle or boat charging systems.

For me, on a rib, I get brain fade and the simpler the system the better hence my suggestion to Bruce - Flat battery? Tighten the screw, start the engine, slacken the screw. Job done and nothing which needs to be remembered....actually, I get brain fade anyway these days. What was your name again?
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Old 21 February 2008, 20:37   #27
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I agree with JW, keep it simple. My experience with two batterys is mainly in an off road vehicle with a diode. However, although this system has saved my A. on numerous occasions, there is a down side. It tends to lull you into false security unless you check the condition of the 2nd battery regularly. Ok, so it still starts but will the 2nd bat. save you if the primary dies? The voltmeter will show everything is Ok even if the 2nd battery has failed. I am going to install a two switch system with no diode and a voltmeter across the common neg. and a point between the alternator pos/two switches. In this way I can quickly check condition of each battery and the combination; no load and loaded and disconnect either one if they look dodgy. Normal running would be both batterys connected. House supply would be from the 2nd battery.
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Old 22 February 2008, 05:34   #28
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In al40's defense, what I will say is that my experience of deep cycle leisure batteries is as he describes and they have a shortened life if they're not kept at maximum charge.

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Old 22 February 2008, 05:56   #29
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The standard "red removable key" switches do not on the other hand like being immersed
Nope! (the one on my old boat died within 12hrs of its swimming lesson......)
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Old 22 February 2008, 06:17   #30
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the simpler the system the better
Battery dies.
1) Remove lid of engine
2) Turn key to "run" positon
3) Put knotted end of rope in sliot and wind rope round handy groove on top of the flywheel
4) Pull.
5) dig out handheld VHF / Garmin handheld & turn on!
I knew there was a reason I like old technology engines!

Granted those of you with V16 800Hp lumps on your transom might need the extra battery.....
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