12v alternator fed relay - bypass yay or nay?
Discussion
Hi all
Not so much a car query as a campervan / electrical one, but browsing forum posts seems someone may be able to advise.
I've got a van (2004 Trigano Tribute aka "Tribby") and the fridge works on electric hook up or gas but the 12v feed when driving (to keep cool in between stops) doesn't work - traced issue; I have the alternator feed to the Tribby's "internal" or "habitation" fuse box (i.e. not the underlying Fiat Ducato's fuses but just for 'campervan stuff') working and have confirmed it's the specific relay for the 12v fridge feed that's knackered.
Problem is that the relay's built into the circuit board so can't just replace and would be tricky to add a separate / replacement relay due to the tiny circuitry involved.
My question is: why not bypass the relay and just power directly? I did a quick test and connected the alternator feed (only provides 12v once ignition on) directly to the fridge 12v mode feed (i.e. bypass the relay) and the fridge powers up (on 12v mode - manual switch on fridge).
I understand the purpose of relays (to an extent) and get that the fridge could be a higher amperage draw, but the only 12v feed is that alternator feed into that habitation fuse box. There's nothing else going to be drawing power from that circuit when driving, plus it only would if you turn the fridge to the manual 12v mode (over gas or electric hook up). Even with it on that mode and assuming it's now sharing a circuit with lower amperage draw things (like what? it's a circuit to the habitation devices, none of which you'd have on when driving?), there's protection both at the habitation fuse box specifically for the fridge (20amp) and even a fuse in the fridge control panel itself (would be a pain to get to but I've got it disassembled at the moment). So where's the harm in bypassing the relay??
Cheers
Ross
Not so much a car query as a campervan / electrical one, but browsing forum posts seems someone may be able to advise.
I've got a van (2004 Trigano Tribute aka "Tribby") and the fridge works on electric hook up or gas but the 12v feed when driving (to keep cool in between stops) doesn't work - traced issue; I have the alternator feed to the Tribby's "internal" or "habitation" fuse box (i.e. not the underlying Fiat Ducato's fuses but just for 'campervan stuff') working and have confirmed it's the specific relay for the 12v fridge feed that's knackered.
Problem is that the relay's built into the circuit board so can't just replace and would be tricky to add a separate / replacement relay due to the tiny circuitry involved.
My question is: why not bypass the relay and just power directly? I did a quick test and connected the alternator feed (only provides 12v once ignition on) directly to the fridge 12v mode feed (i.e. bypass the relay) and the fridge powers up (on 12v mode - manual switch on fridge).
I understand the purpose of relays (to an extent) and get that the fridge could be a higher amperage draw, but the only 12v feed is that alternator feed into that habitation fuse box. There's nothing else going to be drawing power from that circuit when driving, plus it only would if you turn the fridge to the manual 12v mode (over gas or electric hook up). Even with it on that mode and assuming it's now sharing a circuit with lower amperage draw things (like what? it's a circuit to the habitation devices, none of which you'd have on when driving?), there's protection both at the habitation fuse box specifically for the fridge (20amp) and even a fuse in the fridge control panel itself (would be a pain to get to but I've got it disassembled at the moment). So where's the harm in bypassing the relay??
Cheers
Ross
mrrossi said:
Hi all
Not so much a car query as a campervan / electrical one, but browsing forum posts seems someone may be able to advise.
I've got a van (2004 Trigano Tribute aka "Tribby") and the fridge works on electric hook up or gas but the 12v feed when driving (to keep cool in between stops) doesn't work - traced issue; I have the alternator feed to the Tribby's "internal" or "habitation" fuse box (i.e. not the underlying Fiat Ducato's fuses but just for 'campervan stuff') working and have confirmed it's the specific relay for the 12v fridge feed that's knackered.
Problem is that the relay's built into the circuit board so can't just replace and would be tricky to add a separate / replacement relay due to the tiny circuitry involved.
My question is: why not bypass the relay and just power directly? I did a quick test and connected the alternator feed (only provides 12v once ignition on) directly to the fridge 12v mode feed (i.e. bypass the relay) and the fridge powers up (on 12v mode - manual switch on fridge).
I understand the purpose of relays (to an extent) and get that the fridge could be a higher amperage draw, but the only 12v feed is that alternator feed into that habitation fuse box. There's nothing else going to be drawing power from that circuit when driving, plus it only would if you turn the fridge to the manual 12v mode (over gas or electric hook up). Even with it on that mode and assuming it's now sharing a circuit with lower amperage draw things (like what? it's a circuit to the habitation devices, none of which you'd have on when driving?), there's protection both at the habitation fuse box specifically for the fridge (20amp) and even a fuse in the fridge control panel itself (would be a pain to get to but I've got it disassembled at the moment). So where's the harm in bypassing the relay??
Cheers
Ross
Your main alternator output is connected to the battery, I dunno how you've been testing but you'e always going to get 12+ volts at the alternator, engine on or off.Not so much a car query as a campervan / electrical one, but browsing forum posts seems someone may be able to advise.
I've got a van (2004 Trigano Tribute aka "Tribby") and the fridge works on electric hook up or gas but the 12v feed when driving (to keep cool in between stops) doesn't work - traced issue; I have the alternator feed to the Tribby's "internal" or "habitation" fuse box (i.e. not the underlying Fiat Ducato's fuses but just for 'campervan stuff') working and have confirmed it's the specific relay for the 12v fridge feed that's knackered.
Problem is that the relay's built into the circuit board so can't just replace and would be tricky to add a separate / replacement relay due to the tiny circuitry involved.
My question is: why not bypass the relay and just power directly? I did a quick test and connected the alternator feed (only provides 12v once ignition on) directly to the fridge 12v mode feed (i.e. bypass the relay) and the fridge powers up (on 12v mode - manual switch on fridge).
I understand the purpose of relays (to an extent) and get that the fridge could be a higher amperage draw, but the only 12v feed is that alternator feed into that habitation fuse box. There's nothing else going to be drawing power from that circuit when driving, plus it only would if you turn the fridge to the manual 12v mode (over gas or electric hook up). Even with it on that mode and assuming it's now sharing a circuit with lower amperage draw things (like what? it's a circuit to the habitation devices, none of which you'd have on when driving?), there's protection both at the habitation fuse box specifically for the fridge (20amp) and even a fuse in the fridge control panel itself (would be a pain to get to but I've got it disassembled at the moment). So where's the harm in bypassing the relay??
Cheers
Ross
The relay will likely be there to stop the fridge getting a 12v DC connection while your 110/230 AC connection is present.
A relay is essentially a switch in itself it will either kill the positive or negative to the fridge when the relay pole is thrown.
Do you know how the relay is pulsed? Most automotive relays are 12v low ampage circuits energising the relay and then a heavier circuit providing current to the required item (wipers etc).
A relay is essentially a switch in itself it will either kill the positive or negative to the fridge when the relay pole is thrown.
Do you know how the relay is pulsed? Most automotive relays are 12v low ampage circuits energising the relay and then a heavier circuit providing current to the required item (wipers etc).
Thanks both... ok I guess I didn't mean "alternator output" then, I meant "ignition/switched live output".
I.e. that's the 12v feed that only comes on when the ignition is on.
Fairly certain it's the relay as I've traced the ignition 12v right up to the input of the board and then don't get any voltage across the output plug which is right next to the relay. Also directly connected (temporarily) the 12v ignition source direct to the output plug (to the fridge) and I get power there for the 12v battery mode (i.e. bypassing the relay works).
Regarding the mains electric / hook up, you have to manually turn a knob on the fridge* between gas, electric hook up (EHU) and battery operation. So it can't be on EHU and battery at the same time anyway. And as soon as you're ignition is off, that circuit (12v battery mode) goes off.
I.e. you'd never have the engine running/ ignition on AND the EHU plugged in either (can't think of a reason why - you COULD - but then you still have the fridge switched mode anyway?).
I.e. really can't see the harm in having that 12v ignition switched power source direct to the fridge (and it's control mode knob)...?
I.e. that's the 12v feed that only comes on when the ignition is on.
Fairly certain it's the relay as I've traced the ignition 12v right up to the input of the board and then don't get any voltage across the output plug which is right next to the relay. Also directly connected (temporarily) the 12v ignition source direct to the output plug (to the fridge) and I get power there for the 12v battery mode (i.e. bypassing the relay works).
Regarding the mains electric / hook up, you have to manually turn a knob on the fridge* between gas, electric hook up (EHU) and battery operation. So it can't be on EHU and battery at the same time anyway. And as soon as you're ignition is off, that circuit (12v battery mode) goes off.
I.e. you'd never have the engine running/ ignition on AND the EHU plugged in either (can't think of a reason why - you COULD - but then you still have the fridge switched mode anyway?).
I.e. really can't see the harm in having that 12v ignition switched power source direct to the fridge (and it's control mode knob)...?
- Some newer models have an "auto" mode; maybe they knew that would be the case in future so that's an extra redundancy built in...?!?
You need to know the current consumption of the fridge to be sure but....
Calculating on the safe side, let's work on a fridge max current draw of 10 Amps, your fridge will likely take less
There is nothing to gain but plenty to lose if you power the fridge direct from a vehicle ignition supply, the ignition circuit the fridge is connected to could be over-loaded if done this way, fusebox, wiring or the ignition switch could be damaged
Wiring an ignition controlled relay will prevent the above from happening, obviously the relay must be wired to connect a fused battery supply to the fridge
Due to you only finding an ignition supply at the box there is a possibility that there is already a relay up front that is controlling that supply
If there is no relay up front and definitely no main fused battery supply at the box someone has wired the circuit incorrectly
Calculating on the safe side, let's work on a fridge max current draw of 10 Amps, your fridge will likely take less
There is nothing to gain but plenty to lose if you power the fridge direct from a vehicle ignition supply, the ignition circuit the fridge is connected to could be over-loaded if done this way, fusebox, wiring or the ignition switch could be damaged
Wiring an ignition controlled relay will prevent the above from happening, obviously the relay must be wired to connect a fused battery supply to the fridge
Due to you only finding an ignition supply at the box there is a possibility that there is already a relay up front that is controlling that supply
If there is no relay up front and definitely no main fused battery supply at the box someone has wired the circuit incorrectly
Thanks Polly... I think I finally get it now. Sorry, there IS a main supply / battery supply (fused) into the fridge too.
So I guess the ignition controlled relay "activates" a separate circuit for the fridge - which must be powered from that fused battery source?
I think that makes sense
Trying to rewire in a new relay myself I think is beyond my abilities. Looks like sending away the unit for repair will be time consuming and potentially expensive so think I'll go down the route of getting an auto electrician to take a look and fit a replacement relay for me.
Many thanks!
Ross
So I guess the ignition controlled relay "activates" a separate circuit for the fridge - which must be powered from that fused battery source?
I think that makes sense
Trying to rewire in a new relay myself I think is beyond my abilities. Looks like sending away the unit for repair will be time consuming and potentially expensive so think I'll go down the route of getting an auto electrician to take a look and fit a replacement relay for me.
Many thanks!
Ross
I used to work on motorhomes, and the relay was nearly always triggered by the D+ output from the alternator.
If you can, feed a separate relay from D+ and use the existing fused power supply across the new relay to provide power to the fridge.
Generally, on 12v, the fridge runs at a constant 120 watts, so 10 amps is about right. The element for 240v operation is entirely separate, and no harm can be done by running the fridge simultaneously on any or all of the power sources.
The main difference between the 12v and the other two power sources is that there's no thermostat on the 12v. If you drive for long enough in cool ambient temperatures, it's possible to freeze the contents of the fridge.
If you can, feed a separate relay from D+ and use the existing fused power supply across the new relay to provide power to the fridge.
Generally, on 12v, the fridge runs at a constant 120 watts, so 10 amps is about right. The element for 240v operation is entirely separate, and no harm can be done by running the fridge simultaneously on any or all of the power sources.
The main difference between the 12v and the other two power sources is that there's no thermostat on the 12v. If you drive for long enough in cool ambient temperatures, it's possible to freeze the contents of the fridge.
In that diagram is the fuse box the large box at the bottom?
If so no - C & D appear to be the alternator connections and then the red/brown cables is the ignition pulse.
Think of it back in the day with subs and amps (if you ever fitted one) you had a direct connection to the battery but a REM wire that would only turn the amp on when the radio was on - exactly the same process, the REM cable is purely 12v DC with minimal current and the battery cable takes the load.
If so no - C & D appear to be the alternator connections and then the red/brown cables is the ignition pulse.
Think of it back in the day with subs and amps (if you ever fitted one) you had a direct connection to the battery but a REM wire that would only turn the amp on when the radio was on - exactly the same process, the REM cable is purely 12v DC with minimal current and the battery cable takes the load.
Hi, thanks for the response ... nope, the large box at the bottom is the fridge control panel / circuit board itself. The fusebox isn't pictured here*.
The D connection (violet) I can actually see coming into the top of the fridge circuit board itself and can confirm that always has 12v.
The red and brown ignition ones do indeed have 0v with the ignition off and didn't have anything either with it on, until I did the temporary re-wire (relay bypass) to prove that wiring was ok, then I got 12v.
/*I've also attached the fusebox diagram now; it's JP4 (pins 1 and 3 had not voltage across them unless I bypass the relay, RE4). might help! Cheers!!
The D connection (violet) I can actually see coming into the top of the fridge circuit board itself and can confirm that always has 12v.
The red and brown ignition ones do indeed have 0v with the ignition off and didn't have anything either with it on, until I did the temporary re-wire (relay bypass) to prove that wiring was ok, then I got 12v.
/*I've also attached the fusebox diagram now; it's JP4 (pins 1 and 3 had not voltage across them unless I bypass the relay, RE4). might help! Cheers!!
Do you mean JP4 (the plug) or RE4 (the relay)? Here's a photo of them both (relay RE4 centre, JP4 plug to the left):
I've just got hold of a 12v 30AMP 4 pin relay; it's got the the 1, 2 (85, 85) and 3, 5 (30, 7 equivalent, I think) labelling - just working things out but think I may know what needs to go where... will try and put together a diagram and share... thanks again
I've just got hold of a 12v 30AMP 4 pin relay; it's got the the 1, 2 (85, 85) and 3, 5 (30, 7 equivalent, I think) labelling - just working things out but think I may know what needs to go where... will try and put together a diagram and share... thanks again
mrrossi said:
Ok, I've done a diagram with the temp fix / bypass (not ideal) and then what I THINK needs to be done for the fix (new relay); is that right??!?
A thought, if RE4 is tested and proven faulty would it not be better to replace RE4 on the PCBAnyway.....
After removing RE4 (not a good idea leaving it in the circuit) and ensuring battery positive supply is correctly fused, all is good if terminal 2 is negative like 1
Nice fix
Cheaper than getting a pro on the job
Great, thanks...
PCB itself is "scary" to me and I'm trying to avoid touching ! I can cope with the wires themselves but... wouldn't have a clue about replacing or removing RE4. Good point about probably not being ideal to leave in there though... I'll take a closer look / do a bit of googling on how to remove components from circuits. Terrified of breaking something else though!!
PCB itself is "scary" to me and I'm trying to avoid touching ! I can cope with the wires themselves but... wouldn't have a clue about replacing or removing RE4. Good point about probably not being ideal to leave in there though... I'll take a closer look / do a bit of googling on how to remove components from circuits. Terrified of breaking something else though!!
Thanks - I just did a quick google and saw that a soldering iron does indeed seem to be the way to do it. I've only used a soldering iron a handful of times and not have much luck, but that was soldering things together (that never stuck). Just touching it to melt it... yeah I could maybe do that... but need a steady hand (which I haven't got!!) and the components are tiny - may need to get the girlfriend or daughter to help
Ok then
Unfortunately for you the relay is of the plastic sealed type, if it wasn't sealed I was going to suggest that you pull the cover off the relay, remove its armature (moving contact) and cut or break its coil leads where they join to the terminals
http://www.hongfaamerica.com/hq/PDF/HFKC_HFKC-T_en...
Mmmm, RE4 has an open vent hole, water/moisture could have got inside
Unfortunately for you the relay is of the plastic sealed type, if it wasn't sealed I was going to suggest that you pull the cover off the relay, remove its armature (moving contact) and cut or break its coil leads where they join to the terminals
http://www.hongfaamerica.com/hq/PDF/HFKC_HFKC-T_en...
Mmmm, RE4 has an open vent hole, water/moisture could have got inside
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