CALCULATING EXCESS ELECTRICAL CAPACITY

Gs1200robc

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Hi all,

i currently have a 2008 gsa twin cam, i have to say its the best bike i have ever owned.

Like many of us i have the standard lights, fog lights, heated grips etc as well as this is run a sw-motech tank bank that is electrical fed to provide charging for my iphone and i use a icom PMR radio which is powered via a 12v socket.

I am trying to understand what spare capacity the bike has for other such devices such as sat nav etc without affecting the charging of the battery.

Now form what i have read the twin cam gsa has a peak output of 700 watts. At peak i am pretty confident everything is ok, but on longer trips i am rarely at 'peak' more like between 3000 - 5000 rpm.

so doing a bit of GUESS work (please feel free to correct my guesses if you know what they should be) here is a list of what i think i am using:

Standard features of the bike 350 watts?

Heated Grips 100 watts
Fog/Aux lights 35 – 100 watts (each)
IPhone 5 watts
GPS 10 watts
Icom Radio 10 watts

all in i make that 608 watts in total..... now obviously i don't run all these all the time, eg the aux lights are not on that often and the icom radio is only at 10 watts when transmitting.

So can anyone tell me how i can measure the wattage output at 3000rpm and 500rpm so that i can see what i have to play with.

obviously i have read posts on changing to HID lights but i just want to try and understand what the bike has to offer without mods.

any help would be great.
thanks
gs1200robc
 
Can't help you with the electrickity stuff but if it's a 2008 it's not a twin cam....
 
I may be wrong, but I asked a dealer if the bikes leccy output varied with engine speed. His mechanic said that it would give full output at any revs above tickover.
 
2008 GSA is not a twin cam.

Watt is the rate at which work is done. To give you an idea use the formula W = V x A (Volts multiply with Ampere). The alternator output should be about 13.5 to 14.5 V and can be measured across the battery poles with the engine running. You need to determine the current draw when the items are switched on. In any case the alternator would produce the 700 Watts at little over idle speed, current testing on an alternator is carried out at about 2000 rpm or so and the Voltage output should be a bit higher, less than 15 V. The voltage regulator in the alternator would adjust the voltage through the coils to produce the the current that is demanded by the accessories until it is at maximum and will then start drawing current from the battery to top up the demand.
 
Standard features of the bike 350 watts?

Doubt that.. Lots less..
Headlamp on dip/main 55/110watts..
Rest of bike another 50watts to run ignition & speedo functions.
Indicators very intermittent so hardly worth mentioning.
I had a F800GS with 400 watts available & it was loaded with almost every electrical item u needed & it must have been near its limit, never any trouble.
I think you can safely assume to go ahead with adding electrical items.
 
Don't worry about it.

Your iPhone charger, MP3 player, GPS device, charger for your camera and the like won't add up to diddlysquat.
 
Wapping said:
Don't worry about it.

Your iPhone charger, MP3 player, GPS device, charger for your camera and the like won't add up to diddlysquat.
Click to expand...

Indeed.

I run my (real) twin cam with lights, spots, grips, heated jacket and gloves, and it copes just fine :)

As soon as you get above tick over, the charge rate goes right up. The modern alternator is driven by suitably sized pulleys, unlike the crank speed antique on airheads.
 
HID x 2 Heated Grips Heated Jacket Phone and Sat Nav = No Problem :thumb


How old is the alternator belt ? It might be worth sticking a new one on
 
Gs1200robc said:
Hi all,

i currently have a 2008 gsa twin cam, i have to say its the best bike i have ever owned.

Like many of us i have the standard lights, fog lights, heated grips etc as well as this is run a sw-motech tank bank that is electrical fed to provide charging for my iphone and i use a icom PMR radio which is powered via a 12v socket.

I am trying to understand what spare capacity the bike has for other such devices such as sat nav etc without affecting the charging of the battery.

Now form what i have read the twin cam gsa has a peak output of 700 watts. At peak i am pretty confident everything is ok, but on longer trips i am rarely at 'peak' more like between 3000 - 5000 rpm.

so doing a bit of GUESS work (please feel free to correct my guesses if you know what they should be) here is a list of what i think i am using:

Standard features of the bike 350 watts?

Heated Grips 100 watts
Fog/Aux lights 35 – 100 watts (each)
IPhone 5 watts
GPS 10 watts
Icom Radio 10 watts

all in i make that 608 watts in total..... now obviously i don't run all these all the time, eg the aux lights are not on that often and the icom radio is only at 10 watts when transmitting.

So can anyone tell me how i can measure the wattage output at 3000rpm and 500rpm so that i can see what i have to play with.

obviously i have read posts on changing to HID lights but i just want to try and understand what the bike has to offer without mods.

any help would be great.
thanks
gs1200robc
Click to expand...

1/ peak output from your alternator doesnt occurr at the same engine speed as peak engine bhp. Indeed your alternator will likely be able to give you poeak output from something like 2k rpm
2/ starting the bike takes very little out of the battery and so there is little to replace. Once that has happened, the engine demand wont be that big - maybe 50w
3/ your heated grips will be 50 watt max for the pair. The poser spotlights from Nippy Norman are 55w eacg so 110 total. Other bits using your figures make 25 w so a total of 235 say 250 to be safe
4/ your spare capacity would be 450 watts at full alternator output but you would be daft to rely on this. Say 300 to leave a decent safety margin.
5/ but then of course if you are using spotlights you should be using headlights and sidelights too
 
Add a voltmeter to your array. If it's less than about 12.4 volts, turn a few things off. But as Wappers so accurately said, phone chargers and sat-navs use shag-all. It's the stuff that is like a portable arc-welder that's using all the juice.

BTW, your grips probably aren't 100w. See how long you can grip a 50/60w bulb even with a gloved hand.
 
I'd be surprised if the OP's grips dew anything like 100 watts.

By way of example, Oxford Products' quite popular aftermarket heated grips, with their variable control, only draw:
Current drain: Average 3.6 amps per pair (up to 2.0 amps each - 28-30 watts)
Click to expand...

Whilst R&G's offering draw 4 amps or 48 watts, about the highest I can find.
 
this tweaked my curiosity...
I can run my Garmin GPS or phone from the PC USB, which is 5v. A quick google suggests that max current for a PC USB is 100mA-500mA.
So P=IV -> 5V x 0.5A = 2.5 W (Maximum).
I found that interesting :)
 
Any small voltmeter will do the job but ideally get a solid state type as more likely to cope with the weather on a bike. The black lead goes to earth (bike frame) The red lead goes to a circuit that's live with ignition on (rear light for example) and the last lead goes to a wire that's live when the lights are on (either lights a back light or dims the display).

It's that simple. For anyone worrried about damaging the bike, a professional job should be low cost because its a simple job.

You can get LED displays that show red for low volts amber for just enough and green for normal to indicate the system volts. But a gauge that give numbers or especially a moving needle lets you see any changing trends such as the battery degrading.
 
Gs1200robc said:
Hi all,

i currently have a 2008 gsa twin cam, i have to say its the best bike i have ever owned.

Like many of us i have the standard lights, fog lights, heated grips etc as well as this is run a sw-motech tank bank that is electrical fed to provide charging for my iphone and i use a icom PMR radio which is powered via a 12v socket.

I am trying to understand what spare capacity the bike has for other such devices such as sat nav etc without affecting the charging of the battery.

Now form what i have read the twin cam gsa has a peak output of 700 watts. At peak i am pretty confident everything is ok, but on longer trips i am rarely at 'peak' more like between 3000 - 5000 rpm.

so doing a bit of GUESS work (please feel free to correct my guesses if you know what they should be) here is a list of what i think i am using:

Standard features of the bike 350 watts?

Heated Grips 100 watts
Fog/Aux lights 35 – 100 watts (each)
IPhone 5 watts
GPS 10 watts
Icom Radio 10 watts

all in i make that 608 watts in total..... now obviously i don't run all these all the time, eg the aux lights are not on that often and the icom radio is only at 10 watts when transmitting.

So can anyone tell me how i can measure the wattage output at 3000rpm and 500rpm so that i can see what i have to play with.

obviously i have read posts on changing to HID lights but i just want to try and understand what the bike has to offer without mods.

any help would be great.
thanks
gs1200robc
Click to expand...


What is it you need to run that needs the answer to this question? HID's won't make any difference to power consumption if that is what you are worried about.

If it's of use, I run Gerbing Heated clothing in winter, and at full pelt they consume 136W (Jacket 77W, Trousers 44W, Insoles 15W). Over the last few years have had no power issues running all that with HIDs, GPS, Phone etc on a GSA.
 
Last week I went from Oxford to Stafford late at night in around freezing conditions. I had a microfibre T shirt and fleece top under the winter bike jacket and normal trousers under the bike troose. I should have used fleece leggings, but other than that I was warm enough over a 2 hour run.

So heated gear is nice but unless you ride sub zero in thin (i.e. summer) bike gear there's really no need. I'm not after a thread hijack just saying that additional electrical load isnt needed (though no doubt nice to have) until the weather gets really bad.
 
The 1200 twins all use a car-type alternator that has an electromagnet for the rotor. The regulator is able to vary the field current (the current in the rotor electromagnet) to obtain the required output. So it can charge the battery fast even at low revs and wont over-charge or place excess drain on the engine output when not needed.

Your standard motorbike alternator uses a permanent-magnet rotor whose output increases linearly with engine revs. They rely on dumping excess power into a heat-sink when its not needed.
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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