Split charge relay (1 Viewer)

[Snowbird]

Have fitted a new split charge relay onto the camper. Fused it at both ends with a 15amp fuse,but it blew the fuse so replaced with 20amp fuses. All seems well now. What fuses are recommended on these things.

 

[scotjimland]

Have fitted a new split charge relay onto the camper. Fused it at both ends with a 15amp fuse,but it blew the fuse so replaced with 20amp fuses. All seems well now. What fuses are recommended on these things.

Hi Dave .. depends on the cable size..

The function of a fuse is to protect the wiring from overheating and going on fire, (due to a short or overload), so the answer depends on the max current rating of the wire, the insulation class and the ambient temperature.. .. this applies to any circuit ..

Most probably yours is 2.5mm cable which is rated at 17A ,at 30deg C, so a 20A fuse is on the upper limit, but should be fine.... so check wire size and if it is less than 2.5mm , stick with 15A fuse.

 

[Snowbird]

Ta Jim, the wire is fairly thick heavy duty,the type used for spotlights etc.
There is a fuse at the relay end and a fuse at the leisure battery end. The original 15amp fuse blew at the relay end so I swapped it for a 20amp. Then the 15amp blew at the battery end so I swapped that also for a 20 amp.Have run it up this morning and all seems well.

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[Wildman]

thinking about this, you are getting a lot of current possiblly being drawn when you start up (depends how the relay is switched) or a low battery that takes a boost to charge it. Are your batteries ok? where is the relay powered from?

 

[scotjimland]

thinking about this, you are getting a lot of current possiblly being drawn when you start up (depends how the relay is switched) or a low battery that takes a boost to charge it. Are your batteries ok? where is the relay powered from?

yes, that is a good point ..

the problem is that the standard blade fuse isn't designed for surge loads .. it blows fairly quickly ..
I had the same issue with a euro van , once every once in a while it blew the 20A charging fuse.. so I up'd it to 25A .. yes, I know that is naughty .. and I don't recommend.

It would be better if converters fitted a DC MCB or indeed a slow blow fuse, might be worth considering if it's a persistent problem.

 

[Snowbird]

Hy Roger, The relay wont open till it senses power from the alternator,which incidentally is a high output 110amp joby. I think the alternator was trying to push more juice into the batteries than the 15amp fuse would take. The leisure batteries were down as have had little sun,so maybe that was the problem. Since fitting the 20amp fuses all seems well.

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[Snowbird]

Latest update on this is,the 20 amp fuses have started blowing now.
Would an auto electrician be recomended or has anyone any thoughts to save me £45 an hour.

 

[scotjimland]

Hi Dave..

do you know what charge is in the batteries.. you mentioned little sun, I rather suspect that they are low and the fuse is blowing due to the high charge current when you start the engine rather than a cable fault .. can you measure the voltage at the battery terminals ?

edit

are both fuses blowing ?

 

[artona]

Hi Dave..

do you know what charge is in the batteries.. you mentioned little sun, I rather suspect that they are low and the fuse is blowing due to the high charge current when you start the engine rather than a cable fault .. can you measure the voltage at the battery terminals ?

edit

are both fuses blowing ?

This happened recently with my split relay. The fuse was actually burnt rather than just gone. It happened after a prolonged stay on site off hook up so I think the batteries demanded a huge supply

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[chrisgreen]

if you have fused it on the load side(battery)and its that fuse that's blowing,if it was me i would remove the fuse altogether,and just leave it fused on the switch side,or put the biggest fuse you can in it,an altanator will throw a huge current if it needs to,you say you got an 110amp alt when your switch relay switch's to your hab battery the fuse cannot handle the current and if your hab bats are low the current will be huge,to start with:thumb:
let the relay take the load thats why you got a switch relay:thumb:
another thing are you useing a heavy duty switch relay?

 

[Snowbird]

Hi Dave..

do you know what charge is in the batteries.. you mentioned little sun, I rather suspect that they are low and the fuse is blowing due to the high charge current when you start the engine rather than a cable fault .. can you measure the voltage at the battery terminals ?

edit

are both fuses blowing ?

Hi Jim, Theres 12.5 in the liesures,have had an amp meter on the relay wire and theres 25 amps going in.Have put 30 amp fuses on and one of them has now blown.

 

[Snowbird]

if you have fused it on the load side(battery)and its that fuse that's blowing,if it was me i would remove the fuse altogether,and just leave it fused on the switch side,or put the biggest fuse you can in it,an altanator will throw a huge current if it needs to,you say you got an 110amp alt when your switch relay switch's to your hab battery the fuse cannot handle the current and if your hab bats are low the current will be huge,to start with:thumb:
let the relay take the load thats why you got a switch relay:thumb:
another thing are you useing a heavy duty switch relay?

Will try that Chris,have fused it at the relay where the wire comes out to the lesures and just before the leasure bank.Its doung my shed roof in now:Sad:

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[Snowbird]

This happened recently with my split relay. The fuse was actually burnt rather than just gone. It happened after a prolonged stay on site off hook up so I think the batteries demanded a huge supply

Hi Stew,I never have hookup so maybe thats the problem,the battery bank is asking to much of the fuse.

 

[chrisgreen]

Hi Jim, Theres 12.5 in the liesures,have had an amp meter on the relay wire and theres 25 amps going in.Have put 30 amp fuses on and one of them has now blown.

the wire from your alt to the cab bat is not fused?if it is it will be a huge fuse around 150 amp,so going on this the wire from your alt to your hab bat has to handle the same load i would use a heavy duty relay (150 amp)and if it worry's you an inline fuse rated at 140 amps.
what you need is jim to work out what cable size you should run to take a 110 amp load and use this as a starting point,he will need the lenth of the cable run:thumb:
you say there is 12.5 in the bat,the alt will sence this and only throw out what it needs to replace the lost power out the bats.
do some thing for me messure your hab bat when the alt is running,if its 13.8 volt the bat's are not fully charged,and will go up to as much as 14.5(with alt running) before you bat's are charged:thumb:

 

[chrisgreen]

Hi Stew,I never have hookup so maybe thats the problem,the battery bank is asking to much of the fuse.

correct:thumb:

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[chrisgreen]

Will try that Chris,have fused it at the relay where the wire comes out to the lesures and just before the leasure bank.Its doung my shed roof in now:Sad:

ditch the fuses,or put huge fuses in, and only one:thumb:
my little charger runs 70 amps max,the cable's i use are rated at 800 amp
no fuse, straight from the alt to the batteries:thumb:6m in lenth:thumb:

 

[jonandshell]

Expensive, but resettable!
-Obviously sort out the underlying fault first!

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[jonandshell]

ditch the fuses,or put huge fuses in, and only one:thumb:
my little charger runs 70 amps max,the cable's i use are rated at 800 amp
no fuse, straight from the alt to the batteries:thumb:6m in lenth:thumb:

And what happens when that cable gets chaffed and shorts to chassis?

Hope you have a good fire extinguisher!

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[chrisgreen]

And what happens when that cable gets chaffed and shorts to chassis?

Hope you have a good fire extinguisher!

so your are saying the cable WILL get chaffed or might get chaffed, and short to the chassis,when fitting any high ampage cable through a motorhome you must ensure it WONT get chaffed,all down to the instalation,do it right,do it once:thumb:
but i see your point,and as i said put a fuse in it if worried:thumb:
my cables do not run through the motorhome,so no worry of fire:thumb:

 

[chrisgreen]

Expensive, but resettable!
-Obviously sort out the underlying fault first!

Link Removed

no good, it will not handle the direct current from a 150amp alt,it will trip every time the switch relay pushes the power to the the hab batteries:thumb:

 

[bigmillie]

I have used "meter tails" for mine 100 amp double insulated with a 100 amp split charge relay

charges 2 x 110 amp leisure batts up to 55 amps :thumb:

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[chrisgreen]

I have used "meter tails" for mine 100 amp double insulated with a 100 amp split charge relay

charges 2 x 110 amp leisure batts up to 55 amps :thumb:

:thumb::thumb::thumb:

 

[pappajohn]

I have used "meter tails" for mine 100 amp double insulated with a 100 amp split charge relay

charges 2 x 110 amp leisure batts up to 55 amps :thumb:

i hope the cables are well supported !

domestic meter tails are only around 7 or 9 strand 25mm2 (older one were only 16mm2) and wont stand much movement before working loose.

even domestic wiring has been known to come loose due to thermal expansion and cooling.

 

[Snowbird]

OK guys here's an update...I left home this morning,traveled 20 miles,stopped and checked everything as an old truck driver always does.
Found the 30 amp fuse blown in the split charge relay.
Changed it for the same fuse,started engine and left it on tick over for 10 mins watching the battery gauge,all was well so set off again and drove 150 miles,stopped and checked the battery gauge again...bingo,its still charging the batteries from the split charger.
Am now of the opinion that its the initial bang from the alternator that's blowing the fuse....Should I throw the fuses away????...The wiring is all in trunking,so no chance of it chaffing against earth. Am a belt and braces man:Blush:

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[chrisgreen]

OK guys here's an update...I left home this morning,traveled 20 miles,stopped and checked everything as an old truck driver always does.
Found the 30 amp fuse blown in the split charge relay.
Changed it for the same fuse,started engine and left it on tick over for 10 mins watching the battery gauge,all was well so set off again and drove 150 miles,stopped and checked the battery gauge again...bingo,its still charging the batteries from the split charger.
Am now of the opinion that its the initial bang from the alternator that's blowing the fuse....Should I throw the fuses away????...The wiring is all in trunking,so no chance of it chaffing against earth. Am a belt and braces man:Blush:

rewire a new fuse holder in and use a bigger fuse,ditch the blade fuse holder:thumbr if you are happy that you will never get a short ditch the fuse altogether:thumb:

 

[scotjimland]

Am now of the opinion that its the initial bang from the alternator that's blowing the fuse....[HI]Should I throw the fuses away????..[/HI].The wiring is all in trunking,so no chance of it chaffing against earth. Am a belt and braces man:Blush:

Absolutely not .. chaffing and shorting to chassis is not the only risk.. if for any reason the cable is overloaded .. meltdown and fire !

try to source a slow blow or anti-surge fuse or change for a DC MCB

 

[Snowbird]

Absolutely not .. chaffing and shorting to chassis is not the only risk.. if for any reason the cable is overloaded .. meltdown and fire !

try to source a slow blow or anti-surge fuse or change for a DC MCB

Whats a DC MCB Jim.
I did manage to get some slow blow glass fuses and fuse holders,but they are only 20 amp. Havent tried them yet.

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[scotjimland]

Whats a DC MCB Jim.
I did manage to get some slow blow glass fuses and fuse holders,but they are only 20 amp. Havent tried them yet.

Same as you have for the AC circuits in your RV or at home.. (Miniature Circuit Breaker)

http://www.gepowercontrols.com/eu/product_portfolio/residential/minature_circuit_breaker/mcb_ep100uc.html

another style, as given in an earlier post which is easier to install and designed for automotive use as it fits straight into the existing fuse holder Link Removed