Regulator to battery fuse rating

[GSJim]

I will be fixing up some bad connectors on the weekend and may decide to connect the regulator output to the battery through an in-line fuse. The main fuse on the bike is 15A, but searching on the site suggests that I might need a larger fuse for the regulator to battery connection when I go direct instead of through the harness. I found a couple of threads about 20A and 25A fuses blowing, but 30A seems rather large considering the size of the regulator wire.

Does anyone have a definitive answer, or is this trial and error?

Thanks.

Jim

 

[kdo58]

http://roadstercycle.com/Roadstercycle.com Videos.htm
I wired and fused like this video

 

[tom203]

20 amp is good- if it blows, you got problems.

 

[Steve]

In the original wiring diagram, the output of the R/R gets split between what the bike uses and the battery. Basically, the bike is going to take whatever it needs and the battery gets the leftovers. The headlight is about 5 amps, tail light and instruments are only a couple of amps, the coils are about 8 amps, the rest (brake, signals, horn) won't matter until you turn them on. The charging system is capable of putting out about 23-25 amps. Since the bike is already taking 15, there will only be 8-10 left to go through the main fuse to the battery.

If you change your wiring to run the R/R straight to the battery, ALL of the current will go through the fuse that you will want to add to that line. After the fuse, the bike will take its 15 amps and the battery will take the rest, but ALL of the charging system's output will be going through that fuse.

Your choice how big to make the fuse.

.

 

[salty_monk]

30A on mine wired direct to battery. I had a 20A & a 25A blow before I got my hands on a box of 30A's.

 

[GSJim]

Steve, I forgot about the split. The positive wire from the regulator is going to carry the same current no matter which way I wire it. The original harness puts the fuses after the split but the direct to battery connection puts the fuse before the split.

Salty_monk, I think it was your post I read about blowing the 20A and 25A fuses.

The Eastern Beaver kits use 30A fuses.

My final decision on wiring will depend on how brittle the insulation on the regulator output wire is. The stator to regulator wires in the harness were well cooked and very brittle.

Thanks for the replies.

Jim

 

[posplayr]

no matter how you do it there needs to be a fuze between the battery and the red R/R output. The R/R can fail short which will provide a short to ground for the battery.

 

[Steve]

no matter how you do it there needs to be a fuze between the battery and the red R/R output.

I don't think anyone is questioning that part. I think the confusion is "why use a 30, when stock is 15?".

.

 

[posplayr]

I don't think anyone is questioning that part. I think the confusion is "why use a 30, when stock is 15?".

.

Just want to make sure he ends up with that after all of the deliberations .

 

[tom203]

30A on mine wired direct to battery. I had a 20A & a 25A blow before I got my hands on a box of 30A's.

25 amp seems way over- I doubt my 650 size stator could deliver 250 watts on a good day, and no matter how I do the math, the R/R would never deliver 20 amps of DC at 14 volts thru its output.

 

[dr_fosg8]

I can tell you this, I rewired my 1100GL the same way you are doing and started with the 15 amp because that was the size of the main fuse for the bike. The 15 amp fuse inline from the R/R would occasionally blow, I went up to a 20 amp fuse and have had no problems in over a year. YMMV, I have no idea about the 650 charging system.

 

[GSJim]

I don't think anyone is questioning that part. I think the confusion is "why use a 30, when stock is 15?".

.

Exactly. Having cooked two stators and a regulator, I'm very cautious about fusing. I will most likely install an inline ATO fuseholder. I can grab an assortment of fuses at the same time. The ATO fuseholder at the local Crappy Tire has 12 gauge wire so it was really the little bit of wire from the regulator that I was concerned about. However, going directly to the battery does not change the current carried by that wire and there is no sign of heat damage yet (relatively new regulator). I don't have the old regulator to check.

Suzuki could have called the "main" fuse something more descriptive, like charging fuse. If I had taken a closer look at the schematic, I wouldn't have missed the split. I used to design electronic equipment and there is no excuse for me to miss something that obvious.

Jim

 

[posplayr]

Steve,
I don't think the GS electrical needs more than 15 amps . I have measured about 11 amps to the electrical and 4 amps to the battery (average) at 4000-5000 RPM. (I measured this back in 2009 on my GS1100ED)


The fuse depends on how you connect the battery, R/R and electrical together. For a stock configuration it seems to be 15 amps between battery and everything else.

You have to remember that on a cycle by cycle basis (of the 3 phase AC) that when the regulator shunts (or open for series) there is no current flow from the R/R and the battery has to make it up. So at 5000 RPM you can figure on

• Battery will charge 4 amps (average) discharge 11 amps (peak)
• R/R will provide 15 amps average and turns off to zero (minimum)
• The GS electrical (lights, coils, etc) always needs 11 amps.

The main shorting problem is between the battery and everything else. All of the electrical is fused a second time in a multi fuse box system. So the biggest threat is the R/R shorting and grounding out the battery with no other fuses.


I know we have discussed this about what is the difference between running a R/R direct to the battery v.s. to the harness. At the moment it is not clear to me what people do with the normal harness connection when the run the R/R right to the battery through an inline fuse. We have seen people needing 20 amps in this configuration though.

It could be because of the thermal blow properties of the fuse. that when you are continuously running 15 amps through a 15 amp fuse it will blow. So you have to raise the fuse to 20 amps.

In a stock configuration you would use the battery currents I mentioned above in which case 15 amps has a safe margin.

Obviously there is a better short protection with a smaller fuse so retaining the stock "T" configuration and a 15 amp fuse is always preferable to me if you can get the voltage drops low enough in the fusebox and connector blocks.

Jim

 

[GSJim]

Obviously there is a better short protection with a smaller fuse so retaining the stock "T" configuration and a 15 amp fuse is always preferable to me if you can get the voltage drops low enough in the fusebox and connector blocks.

Jim

I think I should check the condition of the existing regulator positive wire before making a final decision. The stator to regulator wires in the harness were definitely overheated (discolored and brittle insulation) but I didn't think to check the regulator's red and black wires.

I would also prefer smaller fuses, which is why I asked my original question.

Thanks.

Jim

 

[tom203]

I think I should check the condition of the existing regulator positive wire before making a final decision.

I would also prefer smaller fuses, which is why I asked my original question.

Thanks.

Jim

Start with 20 amp fuse- carry some extras, but I can't see how a 25 amp would be needed, unless the R/R output spiked for some reason.

 

[Steve]

I would also prefer smaller fuses, which is why I asked my original question.

Not sure why smaller fuses would be "preferred", you really need to go with what is necessary.

Since you have changed the wiring of your bike by re-routing your regulator output straight to the battery, please re-read my post #4.

Feel free to put in as small a fuse as you "prefer" or feel comfortable with, but also feel free to have a supply of larger fuses on hand.

Either way, please report back on your findings. If a smaller fuse does, indeed, work, some of us who are advocating larger fuses would appreciate knowing that a smaller fuse will work.

.

 

[GSJim]

Not sure why smaller fuses would be "preferred", you really need to go with what is necessary.

Since you have changed the wiring of your bike by re-routing your regulator output straight to the battery, please re-read my post #4.

Feel free to put in as small a fuse as you "prefer" or feel comfortable with, but also feel free to have a supply of larger fuses on hand.

Either way, please report back on your findings. If a smaller fuse does, indeed, work, some of us who are advocating larger fuses would appreciate knowing that a smaller fuse will work.

.

By "smaller fuse preferred" I was thinking about using the original wiring and stock T for the regulator output as suggested by posplayr. I have to stop posting before my first coffee is consumed.

I haven't changed the regulator positive wiring yet, just the wiring between the stator and regulator. I thought that going directly from the regulator to the battery through a fuse was a "best practice" for the GS, but as usual you guys have given me more to think about. The final decision will depend on the condition of the regulator positive wire and the wire in the harness. I don't have the original regulator to check. As far as I can remember, the regulator failed shorted and blew the 15A main fuse.

If I make any changes I will update my project thread.

Thanks.

Jim

 

[Steve]

I haven't changed the regulator positive wiring yet, just the wiring between the stator and regulator. I thought that going directly from the regulator to the battery through a fuse was a "best practice" for the GS, but as usual you guys have given me more to think about.

We still consider direct wiring the regulator to the battery to be "best practice".

It's just that, if you do that, you are changing the fusing requirements. The regulator output will not be changed, but, as pointed out earlier, the fuse between the regulator and the battery does not appear until AFTER some of the regulator's output splits off to power the rest of the bike.

It is my opinion that the only reason there is a 15 amp fuse in there in the first place is because before the bike is running, ALL the current to run the bike (lights, ignition, etc.) will be going through the MAIN fuse. After the bike is running and the stator/regulator are doing their thing, only battery-charging current goes the other direction through that fuse, and it probably does not need to be as large.

However, when you wire the regulator directly to the battery, you still need to have a fuse between the battery and the regulator, but ALL the regulator's current is going to be going through that fuse, not just part of it, as before, in the original wiring.

.

 

[posplayr]

We still consider direct wiring the regulator to the battery to be "best practice".

Steve, I can NOT disagree with someone wiring directly to the battery especially if they have one of the older style fuse boxes. However, when you consider the single point power and grounding and all else being equal, I would maintain the "T" as it minimizes current flow between the R/R and battery (on both the + and ground sides). This makes the charging voltage higher if there is corrosion between the R/R and battery. Of course with big leads and clean contacts it will matter little.

It's just that, if you do that, you are changing the fusing requirements. The regulator output will not be changed, but, as pointed out earlier, the fuse between the regulator and the battery does not appear until AFTER some of the regulator's output splits off to power the rest of the bike.

It is my opinion that the only reason there is a 15 amp fuse in there in the first place is because before the bike is running, ALL the current to run the bike (lights, ignition, etc.) will be going through the MAIN fuse.

You are correct that the main fuse has to be sized to run the whole bike. This current is 11 amps when not running and 11 amps peak when the R/R goes into regulation. If it really took 15 amps then the 15 amp fuse would probably blow much more often than it does in practice.

After the bike is running and the stator/regulator are doing their thing, only battery-charging current goes the other direction through that fuse, and it probably does not need to be as large.

As noted above, even when the bike is running, the battery has to supply the full 11amps when a SHUNT R/R shunts or a SERIES R/R opens.

However, when you wire the regulator directly to the battery, you still need to have a fuse between the battery and the regulator, but ALL the regulator's current is going to be going through that fuse, not just part of it, as before, in the original wiring.

.

re my original comment: as a general rule if there is a fault condition you are trying to protect against using a fuse(i.e a battery short), the higher that fuse is the less protection you have. I'm sure there are exceptions but a fuse blowing a 15 amps is better than 18 amps running through a 20 amp fuse and making something hot because it is below the 20 amp fuse current.


Even though we have berated the GS charging systems grounding at length, I think that the (+) power split at the "T" with the main fuse isolating the battery from everything else is good practice and arguably the best practice.


When the R/R is charging the Battery, this schematic minimizes the number of connections and the amount of current between the R/R and Battery while still keeping a fuze between the battery and everything else.

The "T" is really the corresponding point on the positive side as the single point ground is on the negative side. It avoids "current sharing", or in other words splits off the currents as soon as possible (on the positive side) and consolidates them at the last point (on the negative side).

The R/R is still directly across the battery, but of course it is through the stock harness.

 

[salty_monk]

The bike I had fuses blow on used an Electrex stator (the higher rated one) & a Mosfet FH012 RR if that helps...

I haven't tried anything lower than a 30 on my Skunk (STock Stator with an FH012).