Battery isolator: why?

[unbusted67]

Why would you use a battery isolator? Why not just wire you alt into the common on a battery switch and then select 1+2 on the switch when charging and manually select a battery bank when discharging? Isn't the point of having an isolator to prevent the discharge of one bank into another? Why not just prevent it manually?


Sent from my iPhone using Cruisers Sailing Forum

[DeepFrz]

Isn't the point of having an isolator to prevent the discharge of one bank into another? Why not just prevent it manually?

No, the point of having an isolator is so that when you have a brain fart you don't forget to isolate the batteries and end up with a dead house bank and start battery. Notice I said when, not if.

[delmarrey]

Also if you don't have one of those expensive sense type selector switches, switching with the motor running can burn up the alternator. And supposed you put on both with one bank dead.

Better to do it right.

[unbusted67]

Yeah but doing it "right" requires that you sacrifice a volt or almost 10 amps of power to the diodes in the isolator. Is doing it "right" really right?




Sent from my iPhone using Cruisers Sailing Forum

[Greenhand]

As I understand it, an automatic charge relay does a better job, with less loss of power.

[delmarrey]

Originally Posted by unbusted67

Yeah but doing it "right" requires that you sacrifice a volt or almost 10 amps of power to the diodes in the isolator. Is doing it "right" really right?
Sent from my iPhone using Cruisers Sailing Forum

I think that's a bit exaggerated? My combiners hardly show a difference on a digital ohmmeter.

[Dulcesuenos]

Originally Posted by Greenhand

As I understand it, an automatic charge relay does a better job, with less loss of power.

Thats why we have two, one for each stsrt battery

Sent from my LG-LS980 using Cruisers Sailing Forum mobile app

[Dockhead]

Originally Posted by unbusted67

Yeah but doing it "right" requires that you sacrifice a volt or almost 10 amps of power to the diodes in the isolator. Is doing it "right" really right?

Only the diode-type ones, and even those don't lose you nearly a volt (!).

There a number of zero-loss or near zero-loss isolators, made by Driftgate and others, like this one for example:

zero volt drop marine battery isolator combiner

They work fine, although having separate alternators and keeping your start batt and system completely separate works even better.

[Stu Jackson]

Here's why:

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com

Battery isolators were diodes with an almost 1.0V drop! NOT good for charging!

You've just reinvented what had been dismissed as way old technology 20 years ago.

Good work!

[chala]

Originally Posted by unbusted67

but doing it "right" requires that you sacrifice a volt or almost 10 amps of power to the diodes in the isolator. Is doing it "right" really right?

10A of power at 12V is 120VA

Blocking diode or diode battery isolators. From Victron 2 types: Schottky and FET.
Voltage drop for:
Schottky: low current 0.3V, rated current 0.45V.
FET: low current 0.02V, rated current 0.1V.
Power loss in a diode is voltage drop across the diode * current = V*A
Schottky:
low current 10A? 10 * 0.3 = 3 VA, maximum current 100A, 100 * 0.45 = 45 VA
FET:
low current 10A? 10 * 0.02 = 0.2 VA, maximum current 100A, 100 * 0.1 = 10 VA

[Cheechako]

Originally Posted by DeepFrz

No, the point of having an isolator is so that when you have a brain fart you don't forget to isolate the batteries and end up with a dead house bank and start battery. Notice I said when, not if.

Exactly. You switch to "both" to charge the batteries, then the wind picks up and you decide to sail, then you get pasted by a passing squall. By days end you get yourself to anchorage, are tired etc. Next morning you wake up and remember you switched to "both" and the fridge has drained the batteries down to where the engine wont start....

[Stu Jackson]

Originally Posted by Cheechako

Exactly. You switch to "both" to charge the batteries, then the wind picks up and you decide to sail, then you get pasted by a passing squall. By days end you get yourself to anchorage, are tired etc. Next morning you wake up and remember you switched to "both" and the fridge has drained the batteries down to where the engine wont start....

This issue comes up all the time. Many years ago I noted: "If you can be smart enough to run a complicated sailboat, shouldn't you be smart enough to be able to turn a switch?"

Forget the isolators and their voltage drop, either learn to use the switch or do what is suggested in my links above: AO to house bank, relay for reserve bank. Not so hard. Never need to use a switch other than for on/off.

[Cheechako]

Shoulda , woulda coulda....
"should have reefed earlier"
"shoulda put out more rode"
"shoulda rowed over and told that guy he was anchored too close"
"coulda rebuilt that diesel before I ended up in Bora Bora.."
"if I woulda listend to others I'da bought a RIB before I spent $ on 3 other types of dingys..."
The list never ends.... There are other options than an isolator though...

[Maine Sail]

Last summer I get a call from the YC manager saying a transient was towed in the night before and needs electrical assistance.

Boat had motored all morning then sailed up from MA somewhere and it was getting late and the wind had died. Owner attempted to start the motor and could not even get a click, click... When he shut the motor off he forgot to switch off BOTH... Dead batts, as in 3V when I got there. Batts were probably dead before he forgot to switch off BOTH because the alt was toast and he never knew it.. There was not enough wind to battle the tide, they tried for four hours, before ponying up for a tow.

Get to boat.

#1 Owner had been "charging" on BOTH only alt was dead.
#2 Owner had nothing but an analog volt meter that was grossly misrepresenting and not very visible
#3 Alternator had died, blown diodes, and they never knew it until it was too late.
#4 Batteries were AGM and by the time I tested them they were toast.
After a barrage of questions to the owner is was decided the alt had apparently died four days prior when he asked his son to switch to BOTH..

Consequences of these errors:

Tow = $$$$$ (did not ask what it cost, considering..)
Ruined AGM Batteries = $$$$$$$$
Lost three days of a Maine Cruise vacation = Priceless
Pissed off Wife & Scared Son = Not Good!


While no one today uses Betamax no one today really installs diode isolators. Diode isolators are akin to Dinosaur saddles they have been replaced by better products. Still...

*Even a diode isolator would have left him with one good battery

*An Echo Charger would have left him with one good battery

*A Combiner or ACR would have left him with one good battery

* The BOTH position & HEF left him dead in the water.

HEF = Human Error Factor


The Rx:

Installed Echo Charger
Installed new batteries (he still insisted on AGM)
Added Voltmeter In Cockpit Engine Panel
Diirect Wired alt to house bank because the diodes were blown, which is usually a switch error...
Made a few other minor wiring tweaks to better help the AGM's charge better and hopefully last a bit longer..


Moral? BOTH Works fine, humans make mistakes. Isolators, Echo/Duo Chargers and combiners/ACR's do not "forget"....

BTW it is only August and I am on my fifth blown alt repair from battery switch position blunders.......

[rwidman]

Originally Posted by unbusted67

Why would you use a battery isolator? Why not just wire you alt into the common on a battery switch and then select 1+2 on the switch when charging and manually select a battery bank when discharging? Isn't the point of having an isolator to prevent the discharge of one bank into another? Why not just prevent it manually?


Sent from my iPhone using Cruisers Sailing Forum

Why not have it automatic? Is the cost bothering you? It's under $100.