Battery Isolator HOT

Submitted: Friday, Mar 11, 2005 at 15:25
ThreadID: 21147 Views:4142 Replies:6 FollowUps:9
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Hi guys and gals,

Following on from advice from this forum I have just finished fitting a dual battery system with a Redarc Isolator beween the start and aux batteries to my 3 l diesel Hilux..

All seems to be working well, however the isolator gets pretty hot when the vehicle is running. Is this normal?

For those interested the costs (in Canberra) where

Battery tray from Supercheap $16
520 cca battery (the largest that would fit the engine bay space) $139
Redarc Isolator (the cheapest price I could find in Canberra) $180
Battery cables $70
Homemade battery hold down clamp, 6 pack

Cheers

Buggerlux
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Reply By: Member - Luxoluk - Friday, Mar 11, 2005 at 17:08

Friday, Mar 11, 2005 at 17:08
Same issue applies to the ARB solenoid as well. Until the main battery voltage drops to the predetermined level the solenoid maintains the two batteries in the engaged position. If you draw some power after turning off, eg lights/fan you will hear the solenoid disengage after a few moments. This is one way of disengaging them. I have put a switch on the earth lead to overcome this issue and basically can leave the battery off charge particularly where the trips are short around town. On a trip away where I need to get it up to a full charge and maintain it I just simply leave it switched to earth. Cheers
AnswerID: 102085

Reply By: Wisey (NSW) - Friday, Mar 11, 2005 at 18:13

Friday, Mar 11, 2005 at 18:13
Hi Bugalux,
Is yours a 3L motor (2.8Ltr) or 3Ltr, did you fit your aux' battery on the side behind the left headlight, near air filter box? You said that was the biggest aux' batry?

Regards
Andy
AnswerID: 102091

Follow Up By: timber - Saturday, Mar 12, 2005 at 09:39

Saturday, Mar 12, 2005 at 09:39
Andy,

A 3 l, and yes fitted behind the left hand headllight. The size issue was one of length, the snorkle, power steering pump resevoir and radiator overflow bottle restricted the length. At the battery shop we tried various sizes in the tray, however I was reluctant too fit a battery that "rubbed" up against any "bits and pieces".

Since this post I have been incontact with Redarc, they advise that the unit is designed to run at 70 C. I guesss that is pretty hot.

Cheers

Buggerl
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FollowupID: 359935

Reply By: Mainey (WA) - Saturday, Mar 12, 2005 at 10:24

Saturday, Mar 12, 2005 at 10:24
(Quote extract)Following on from advice from this forum I have just finished fitting a dual battery system with a Redarc Isolator between the start and aux batteries.
The isolator gets pretty hot when the vehicle is RUNNING.
For those interested the costs (in Canberra) where
Redarc Isolator (the cheapest price I could find in Canberra) $180
BATTERY cables $70
Buggerlux(end quote)

timber, essentially you have paid $250 for a solenoid system after you have received advice from this forum, bugga, it would have paid you to buy one interstate, pay the postage and save yourself at least $80… or buy something else?

Said very simply, heat is the consequence of power (voltage) which is being used directly by the isolator to maintain its ability to operate, eg; open and close the metal contacts against the mechanical force applied to it; therefore this power is not being used to run your fridge, so quintessentially it is only being wasted.
Isolators, due to their very technique of operation and because they are using your battery directly as a power source to remain closed, do get ‘warm’ in use, the difference between warm and hot is what is questionable.
AnswerID: 102152

Reply By: TheUndertaker - Saturday, Mar 12, 2005 at 11:05

Saturday, Mar 12, 2005 at 11:05
After reading your post I checked if my rotronics became warm/hot [70c seems bloody hot to me] while engine running and with engine off ,no temp change either way , my way of thinking would suggest that the heat your unit is generating is a FAULT [nevermind that redarc say is normal]. To generate the heat you are losing power ,amps/volts that should be flowing into your aux battery ,
AnswerID: 102156

Follow Up By: timber - Saturday, Mar 12, 2005 at 11:38

Saturday, Mar 12, 2005 at 11:38
Undertaker,

The exact response from Redarc was:

Under normal operating conditions the solenoid will be around 70 degrees
C.

Kind Regards
Paul Savage
Customer Service Engineer
REDARC ELECTRONICS PTY LTD

Cheers

Buggerlux
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FollowupID: 359946

Follow Up By: Mainey (WA) - Sunday, Mar 13, 2005 at 06:36

Sunday, Mar 13, 2005 at 06:36
Undertaker,
the Rotronics unit fortunately is an Electronic Isolator, and not a Solenoid, hence negligible voltage drop and no '70' degree heat build up that I suggest would be using precious voltage, that could otherwise be powering the fridge, and causing some inherent voltage drop!
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FollowupID: 360001

Follow Up By: Mad Dog (Australia) - Tuesday, Mar 15, 2005 at 11:47

Tuesday, Mar 15, 2005 at 11:47
Probably didn't get hot because your aux battery was charged. A semiconductor that doesn't get hot when passing large currents hasn't been invented. They get far hotter than a mechanical relay.

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FollowupID: 360200

Reply By: Wok - Sunday, Mar 13, 2005 at 08:03

Sunday, Mar 13, 2005 at 08:03
Bugger Lux,

The Redarc dissipates about 5.5W when ON[control unit has negligible loss]. This translates to about 450mA. The reason it feels hot is because the themal path is not as good as a metal-jacket solenoid. I measured the impedance of an Ashdown hd silver job = 15.6ohms c.f Redarc = 28.2ohms, which means the Ashdown generates even more heat[sees alternator voltage while my Redarc sees 12.5V]

At ambient of 21.9oC the + terminal was 39.1oC after 1hr [supply@14.1V] As the unit was not mounted on metal, this is a 'severe' test?

Redarc could improve the control unit by dropping the holding-current.

Anyway as the vehicle is usually moving when the Redarc is ON there will be some cooling from airflow?

cheers
AnswerID: 102214

Follow Up By: Mainey (WA) - Monday, Mar 14, 2005 at 20:08

Monday, Mar 14, 2005 at 20:08
(Quote)The exact response from Redarc was: Under normal operating conditions the solenoid will be around 70 degrees C. (end quote)
So why does the Redarc solenoid run at 70 degrees, what causes this added heat, and does it happen to all solenoid systems ???
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FollowupID: 360146

Follow Up By: brett - Monday, Mar 14, 2005 at 21:56

Monday, Mar 14, 2005 at 21:56
A solenoid is a coil of wire, just like a heater element, so it will generate some heat, as Wok has calculated above, the coil will need to dissapate approx 5W of energy, mostly via heat. If you can comfortably touch it then it's probably not too hot. Assuming the heat is coming from the coil then no worries about voltage drops as the coil only operates a lever to close the contacts. Now if the contacts are generating the heat then you have a problem.
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FollowupID: 360159

Follow Up By: Wok - Monday, Mar 14, 2005 at 23:50

Monday, Mar 14, 2005 at 23:50
Mainey,

Brett has said it all.

If I were worried about solenoids I would have to dump my Toyo, the fuse panel is full of relays for lights etc. After 21 yrs the venerable lady has all her original relays.What vehicle do you know off that has all solidstate switching? Even my old hd metal clunker[isolator] has been switching on/off everyday for God knows how long.

If you think 70oC is hot, try measuring the back-housing of your headlights after running for awhile.

cheers
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FollowupID: 360175

Follow Up By: Mad Dog (Australia) - Tuesday, Mar 15, 2005 at 11:27

Tuesday, Mar 15, 2005 at 11:27
5.5 watts is very little compared with what semiconductors have to dissapate when passing large currents. A mosfet passing 40 amps will dissapate about 20 watts will need heat sinking and get bloody hot but they are rated to about 180c but don't really let go till about 300c. Hard to beat the good old fashioned relay.
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FollowupID: 360199

Follow Up By: Mainey (WA) - Tuesday, Mar 15, 2005 at 17:40

Tuesday, Mar 15, 2005 at 17:40
It was not my post that claimed (Quote)Since this post I have been incontact with Redarc, they advise that the unit is DESIGNED to run at 70 C. I guesss that is pretty hot(end quote)
my own thoughts are if the unit is actually designed to run for some reason at 70 degree's, then why not modify the design slightly to allow it to run cooler???
or is the heat required for some obscure reason???
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FollowupID: 360242

Reply By: MrBitchi - Monday, Mar 14, 2005 at 09:30

Monday, Mar 14, 2005 at 09:30
My Redarc runs hot too. Not a fault, just normal operation according to Redarc. Been in nearly 2 years now and no problems.

Cheers, John.
AnswerID: 102337

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