Where Can I Get This Weekend

[DR SCHNITZEL]

Just ordered some resistors for my 1600 kg secondaries. This was 2 weeks ago now and they still are not here. Does anyone know what resistors to get and where to get them from this weekend. Im single turbo complete minus mapping once i get these. Its taken 3 months!!! So far:driving

[Prof]

If you order from Farnell (www.farnell.com) or RS (rswww.com) then they will be with you tomorrow.  You could also try Maplins - they have stores in most towns, but may not have the values you want.

[DR SCHNITZEL]

cheers for that Prof.
 
I just need to know what ones to get. there are quite a few to choose from.
 
ANYONE?

[Prof]

I\'d go for 8.2 Ohm and 10W or 15W - but that\'s just me - that\'s based on the injectors having an impedance around 4 Ohms

[DR SCHNITZEL]

I just bought some 7.8 Ohm 12W, will these be ok do you think Prof>?

[Prof]

I just bought some 7.8 Ohm 12W, will these be ok do you think Prof>?

Reckon you\'ll be ok with them.  It\'s not like they\'d be on all the time either - and when they are there not driven on fully - only pulsed - so they will only dissipate siginificant heat at WOT - people don\'t tend to sit with the throttle down hard all the time
 
Make sure they got some \'breathing room\' - bit of air around them

[DR SCHNITZEL]

Ok cheers prof i also bought ones similar to what you suggested but they are 12watt 8.2 they didnt have 8.2Ohm 10w or 15w.
 
what difference will these make? i dont fully understand the maths

[dandan]

I don\'t understand what the resistors are for full stop.
Is this something that requires doing when running 1650 injectors? I\'ve never heard of needing to put something like this in, although I\'m far from the font of all knowledge, could you explain the reasons behind it?

[DR SCHNITZEL]

there was also close to 50,000 types of resistor i could have bought.
 
They essentially reduce current flow so a circuit in the pfc doesnt overheat?
 
Am i right.
 
I thought resistors were simple, but there are tooo many types.

[Prof]

Resistors are basically just a way of limiting current flow in a circuit - if you take a look at Ohms Law - R = V / I or to write that another way - V = IR - you can see that Voltage, Current and Resistance all work together.
 
In the example of your injectors - let\'s keep it simple and assume the car voltage is 12, and the injector Resistance is 4 Ohms.  Without a resistor, the current going through the injector would be 12/4 = 3 Amps !
 
If you wire in an 8 ohm resistor in series, the resistance is now 8 + 4 = 12.
 
The current is now 12/12 = 1 Amp.  So the resistor has limited the current to 1 Amp.
 
 
The reason for the great variety of resistors is that they come in various packages to handle different power dissipatons - and also are made from different materials - Carbon, Metal Oxide, Metal Wire - the choice of material will depend on what the applicaton is  - some materials are better suited to high voltages, some are more stable under wide temperarture changes.  Most power resistors are either metal wire or metal oxide, and come either in a Ceramic housing or an Aluminium heatsink housing.

[DR SCHNITZEL]

Superb, so why is it needed. some people say its not needed for these applications. what are the pros and cons?

[Prof]

Some aftermarket ECU\'s have current limiting built in to the injector drivers, so if you do wire low impedance ones, the ECU is protected.  However, it\'s not necessarily the case that the injector is protected.
 
The Bosch Injectors can take a large current spike to start with, but are designed to operate with a lower \'holding\' current once fired - hence the term Peak and Hold.  If the injector spends too long being fired at the higher current with no series resistor, then it could burn out - but given these things only fire part cycle if at all under normal driving loads - you should be ok - that seems to be peoples experience.

[DR SCHNITZEL]

Great Prof cheers. They arrived today. I think if i can keep my hat on ill fit them tonight. only 3 quid posted for the 2