mk3 build thread

[B-chi]

My laptop has died so I can't post up pics. I did have 4 powerplants but was only running 2 of them & I've now got a fusion nv in a 3cuft box tuned to 30hz. made from Inch thick mdf & a 2 inch baffle with the subs recessed in.

I'll see if I can email the pic to photobucket. 

[B-chi]

[IMG]http://i369.photobucket.com/albums/oo137/B-chi/Golf/photo.jpg?t=1247658818[IMG]

[autoelec]

Thanks for the reply.

Deep cycle batteries are what some people call Marine batteries, they are not ideal for this use and not much good for starting cars on a regular basis either, I just hope this helps someone before they buy the same type.

There is a lot of missunderstanding about electrics, its not voltage drop you get from high resistances its current drop, there is a big difference between the two.

Going big on the cables does reduce resistance and allow higher currents to flow but go too big and they become too stiff and can suffer from fatigue fractures internally where the engine moves for example. As there is a maximum of 70 amps from the alternator regardless of the cable size going that big is a waste of time and money, something to remember for next time.

Regarding soldering, its an urban myth that its not a good idea to solder, all joints should be soldered, just crimping any connections is not a good idea and can cause crackling and poor performance due to the higher resistance connection - allways solder all connections, crimps are only for connectors that must be removable.

Thanks for taking my posts in the way they were intended, just trying to help

[B-chi]

I thought marine batteries were designed to withstand salt corrosion and that they can be deep cycle or engine start or both. How else would they start boat engines? Also these batteries are suited to large ups battery banks. Where they'll be discharged then recharged & kept floating until there discharged then recharged again.

If The current goes up, doesn't the voltage drop. If my alt puts out 70amps but has high resistence through small cable, the current getting to the battery will be less than if the cable was thicker with less resistence, surely?

Also in aerospace applications all the connections are just crimped. The vibration causes solder joints to fail apparently. Crimp connections, done properly, are better as they are pretty much copper on copper. Solder is not as good a conductor. Spoke to my old man who works with space satellites & such

[autoelec]

Marine batteries are deep discharge batteries, but are desiged for powering auxillary systems only, you use different batteries for starting the engines, yes I do own a boat and have 1st hand experience of this in addition to my industry training and more than 30 years of experience.

Quote "If The current goes up, doesn't the voltage drop" NO, the two are seperate, voltage remains the same throught the circuit only the current changes. Resistance causes a reduction in current flow, it does not change the voltage.

Try the following, get a multistrand cable connect it in a heavy duty circuit then cut all the strands except 1, the voltage will be the same, but it wont allow sufficient current to flow. Think of current like you would water flowing through different sizes of pipe, compare how a hose pipe and windscreen washer tubing can flow different amounts of water through them.

A lot of people are confused by this.

A few years ago I worked at Rolls Royce as a Queens Flight engineer and inspector on helecopter systems, you are correct that crimps are used in such applications, however the current requirments are lower, the cables and connectors very carfully matched, they are also subject to regular checking and testing and regularly fail and have to be repaired or replaced. A very high percentage of cables fail testing at their regular "flight hours" inspections.

You are also right that solder does not conduct as well as copper, however a soldered joint is more suitable for the hostile environment in a car so the benefit gained outweighs the very minor downside.

A properly soldered joint has a much longer lifetime than crimps and when done properly, without excess solder flowing outside the joint will not affect the strength of the joint, a badly soldered joint with solder flowing down the inside of the cable through capilary action is another matter. Its all about using the correct temperature for the solder being used and the correct size of soldering iron for the job.

If soldering was such an issue why are so many circuits such as ecu's and amps soldered inside? They dont use crimps inside the amps do they?

I specialise as an auto electrician and car electronics and diagnostics.

Eric

[russ-vdub]

Wow really interesting read. I'm an electonic engineer so can understand whats going on. Thanks for the info Eric, even tho its not my thread lol!

Loving the standard of installation B-Chi, its really nice to see things done properly for a change, the amount of bodge jobs i've seen is just unreal! Good work lad, look forward to seeing more

[B-chi]

I thought Current and voltage are linked, you cannot change one without changing the other. Ohm's law!

Can't deep cycle also be suitable for engine starting. I know optima do them. Doesn't deep cycle just mean the battery is capable of discharging more than a standard battery without damage.

My deep cycles havebeen working fine starting the car for the last few months. I also know people with proper big installs that have been starting cars with deep cycle batts fine for years.

When I start the car the voltage drops to just under 12v. When a big bass not hits that 2 can drop the voltage so isn't starting jut the same as a heavy bass note. It requires a large amount of current to start the engine. Well I've got upto 2500 amps on each of my batts for 5 secs!

I'm nit trying to claim to know everything. I like to learn about things I'm interested in & some of what your saying goes against what I've learnt so far.

[autoelec]

None of us know everything, I learn new things every day.

Ohms law is all about the relationship between voltage, current and resistance. What you are seeing is called voltage drop, the voltage should be the same throught the circuit, check at any two points on the system, if it varies at all you have found a high resistance in the circuit, that should be fixed.

The fact that your battery voltage drops is down to the load put upon it by the high resistance starter and the amps, the battery can only provide a limited output, that is where it all gets complicated to explain.

This is why there are different types of battery, made from different materials, there are some batteries that are a compromise between a deepcycle battery and high power battery that aim to provide a mid-way house between the two, most battery manufacturers offer them, but ask about capabilities and my experience has been that the answers become a bit vague, they normally suggest that you are better using the correct type for the purpose, but you can use these multi-purpose if you want.

My own experience is that the multi-purpose batteries tend to have a shorter life when used in a fast discharge environment such as starting and other high power uses like amps. I can only suggest you contact the battery manufacturer to get advice based upon the best type for the particular purpose you have in mind.

I bought 4 deep cycle gell filled batteries for my boat (at £225 each) that were supposed to ideal for my boat with 2 for starting and the other 2 for lighting, tv, fridge etc, the two used for starting only lasted just over a year, the manufacturer declined the warranty on the basis that they were only intended for occasional starting and as I was starting both engeines about 4 times every weekend that they had been excessively used.

I have fitted dual optimax batteries to a number of 4 wheel drive vehicles, 1 yellow top and 1 red top, one for starting the other for the winch with great sucess. I fitted  split charge systems at the same time.

Eric

[ianw3321]

Current drop ouch

[ianw3321]

On a serious note bichi, although I admit that I am inexperienced with car audio I am however a qualified auto electrician with city&guids etc, and have been a hifi enthusiast /modder / diyer for years and while everything you say about ohms law, voltage drop and keeping resistances as low as poss to minimse the dreaded voltage drop which is as relevant in hifi as it in car audio but where I disagree are your views on soldering. In my opinion copper to copper crimped connections are a no no as copper oxidises leading quickly to a dodgy connection as for solder it is not brittle it is soft, standard solder may not conduct as well as copper but specialised hifi silver loaded solder available on ebay and elsewhere is. Such solder and gold plated connectors are the norm in hifi. I can however see the practical problems of soldering in the car. If you must use crimped connections then silver plated cable (which does not oxidise like copper) and plated connectors although expensive are a must for high quality audio appliications. Your further views on this subject would be appreciated.