BC

Interesting. Tons of cars out there with no hood on the back, let alone the pipe hooked in properly. They drive for long periods.

j.kenzie@sbcglobal.net

The fan must move quite a bit of air. The duct and hood might give cooler air, but he fan still pulls air, usually hot air with no hood, from the back of the alternator and discharges through the front. That makes it about the same as an open case design.
Dave

SeanR

Thanks Stan for the check list.

Mrmerlin

Your welcome Sean,
I had an 80 or 81 928 I was working on with a Paris Rhone alternator,
I was seeing charging at 14.3 to 15.1, I started to smell acid after parking the car in the garage,
and upon further investigation the battery was dripping acid out of the vent and filling the battery box.
A new PR regulator brought the charge back to 13. 3 to 13.7 battery stopped boiling.

With a AGM battery you dont have the liquids , it is a gel
but it may get hot sitting in the unvented battery box,
thus the suggestion to hit it with a IR gun after running the system to collect data

Belly pans would be a good idea to isolate the alternator from errant sand/stone/ dust
I had an alternator on an 85 without the air hose but it did have the duct and it was filled with crud,
the leaking PS didnt help.
I had to take the alternator apart to clean out the stones.
This wasnt the first alternator filled with stones and sand.
But good point a lower engine cover would be the hot ticket

TXBenchRacer

MrMerlin I've seen a few boil over over the years many times due to insufficient grounds

My dd is running a twin alternator batt setup pushing a total of 600 amps twin 300 amp units puishing a consistant 15 volts it's been on the road running this setup sense 2008
Not once have I had a single battery or main fuse block issue. 99% of the time people don't use the correct guage wire for the amp load being given.

TXBenchRacer

Lt I've got a few picks in my photo album in my profile

Hessank that's a good question..... In our planning and doing we forgot to take measurements of the amount needed a good rule of thumb is to take the distance between and add 4 feet for the bends dips and curves of the chassis


I'll have some more photos up tomorrow but it's been a hellish nasty hot 105 day so I'm calling it a night

Also side note case temps are no issue with this unit as it has 3 internal fan assemblies...

Koenig-Specials 928

Thanks you. I now have my winter project.

j.kenzie@sbcglobal.net

Hi TX,
The way I understand the stock electrical system is that the long battery cable goes from the starting battery to the starter. It is sized for the starter load. The starter connects to the alternator and then to the jump post and main fuse panel. The alternator runs the cars accessories, and recharges the battery. The charging current is not very great.
I assume for your application uses the battery connection in the rear as a junction point for large amps, and that is the real reason for the larger cable that goes from alternator to starter to battery to amps. When I upgraded my alternator, I upgraded cables from alternator to jump post, and to starter, but I don't run big amps so I left the long battery cable alone.
Am I missing something?
BTW nice job,
Dave

TXBenchRacer

In a ideal charging system the batt runs the system the alt maintains the level the stock unit just is not up to the task at hand when a stock system in under load it has far to much voltage drop

If your not pulling or pushing large loads your in the green
Here is a wire guage chart to help as a rule of thumb you never want to see more than a 3% drop between points if you have 12v at the batt and 11 at the ce then wire guage needs to be increased.
That's ideal there is a small amount of wiggle room
12 (V) x 3% = 0.36 (V)

And thanks I just wasn't happy with what was out there so why settle.

dr bob

The charging current is determined by the impedance of the battery (and cables), and the available charging voltage. Many modern cars charge at 15 volts now, and the batteries seem to survive OK. Regardless of whether you charge at 14 or 15 volts, you should have the battery vented externally. The sizing of cables needs to respect the loads, and the amount of voltage drop you are willing to accept from the cable resistance. The loads at the CE panel are not going to magically increase a lot with a 1 Volt increase in charging voltage (about 6% for the resistive loads like lights and blower motors), so the original wiring ** in good condition ** beteen the jump post and the CE panel will be fine for the original loads there.

Most folks add load at the battery end for high-power car audio, and at the jump post for serious lighting and cooling fan upgrades. The connection between the alternator and the jump post needs to be up-sized for any added loads, with a derate for the fact that it's in a sheath with the other wiring, and for the engine bay operating temperatures it sees.

The battery to starter cable needs to consider the alternator capacity, the expected loads at the battery end including the fuel pump, injection, cooling fans, plus whatever a user adds in the way of audio or other loads, plus the normal charging load for the battery. The cable is exposed for virtually its whole length, so doesn't need a derate for temperature if installed in the factory location.

The alternator to starter cable also needs to consider alternator capacity and the same loads as the battery to starter cable, less the starter load. It gets a derate for heat and sheathing. The 8mm stud on the super-capacity alternator would bother me if I were regularly using full alternator capacity, but that's not something easily changed. When you fabricate and install cables, use lugs with the correct hole size, add copper washers, and install them so the highest-load cable is closest to the alternator on the stud. With heavy cable there, I'd use a self-locking nut to keep engine movement from loosening the connections there.

The cooling will be critical under high loads. As much as it sounds like overkill, I'd probably go shop for a marine duct-mounted bilge blower to add to the hose from the front wheelhouse, especially for a car that was going to be running but standing still while showing off a mega sound system. Fabricating a shroud will be a challenge in the tight quarters under the car, especially considering the open-frame design of the big alternator.

dr bob

When designing real electrical gear, consideration is always given to available short-circuit current and protection devices. Therea re no protection devices in these circuits, so one has to decide how big a meltdown and fire can be "acceptable".

jcorenman

Dave, this is correct. The only missing piece is that I suspect he is feeding the big amps from the battery.

Normally, the battery supplies high current (around 400 amps) to the starter for 3-5 seconds to start the engine, which maybe uses one amp-hour (out of a capacity of 20-40 depending on battery age). Then the battery slowly recharges as the engine is running, while the alternator supplies all of the vehicle loads. Most of those loads come off the CE panel, but some-- engine electronics in particular-- are direct from the battery.

One reason that there are lots of different experiences floating around is that battery charging depends on temperature, and time. When a battery is discharged it will happily accept very high currents and use that energy in the chemical reaction to recharge itself. But once charged, if the charge voltage remains high, then all the battery can do is convert that energy into heat, and decompose the battery water into oxygen and hydrogen (and sulfuric acid into something stinky).

The battery's "float voltage" is the voltage where it no longer accepts any current, once charged-- it can be left on the float voltage forever, just maintaining its 100% charge. A higher voltage will push current into the battery, heating it and breaking down water. That float voltage for a flooded lead-acid battery is around 13.4 volts at 25C (77F), and a couple tenths higher for AGM's.

And that float voltage depends on temperature, dropping around 4mV per deg C. Not a lot, until the battery starts getting really warm. That is spelled "thermal runaway".

Some people drive a mile to work or to the store with temps in the 50's or 60's, others start the car and then drive ten hours across a couple of states with temp's well over 100. The factory system has to work, for both.

I think the stock system is aimed at charging the battery a little over float, and then aggressively cutting that back as temperatures increase-- hence the common complaint of low charging voltage. But for the case where we start the car and then drive across three states in the summer, it works pretty darned well.

There is usually no battery temperature sensor in automotive applications, but it is common for cruising sailboats where the goal is to recharge the "house bank" (typically 500-1000 amp hours) as quickly as possible. The point of control is at the alternator regulator, so-- for cars-- building the temperature compensation into the alternator is the simplest solution.

What TX is doing here makes a lot of sense, for his application-- supplying huge amounts of current with nearly-constant voltage to his sound system. If his amps are connected directly to the battery then he needs big fat wire all the way from the alternator to the battery. He also wants an AGM battery (Optima or whatever) for lower internal resistance-- because the batteries will still need to help during the peak of the bass notes, when brains turn to jelly-- and he wants a high charge voltage to help the battery recover charge quickly. And that alternator is a true work of art, I wish I had one for the boat when we were screwing around with rewound truck alternators.

But 14.8 volts is too high a charge voltage, long term. Once the battery recharges it will just start heating, in its little box sitting next to the exhaust pipe and bathed in the hot air from the engine and radiator. The hotter the battery gets the more the float voltage drops, and the more current it will accept and turn into heat. It might last an hour or two, or longer if the temp's are cooler.

All it would take to make this perfect would be an external voltage regulator for the alternator, with remote sensing of battery voltage, and temperature. That moves the point-of-regulation from the alternator, where it doesn't matter, to the battery where it does. Then, as the battery reaches full charge and starts warming up, the charge voltage drops accordingly. These kind of regulators are common on larger boats. I've never seen one used for an automotive application but this would be the perfect application. Here's one choice: Xantrex.com (no affiliation).

Cheers, Jim

Alan

Jim, agreed - I had made the same point in a previous thread on this. 14.8v is too high for a general usage model - maybe it will be OK here. For me in Phoenix it would eat batteries very fast - I'd suggest its a not a great idea for anyone who needs great reliability for year round use in varied climates.

Now you could use a different or variable regulator in a similar set-up but set to a lower voltage.

Dr Bob - the case vented styles usually have 2 fans one at the front and one at the back.. they pull from both ends and eject from the middle case vents - a shroud at the back like the stock one would still feed cooler air to the regulator and rectifiers - the biggest heat sources - so well worthwhile (I'd do this in similar to stock config). Not sure if this one is configured like that - but I'd think it would have to be...

You only get more current out of a big power alternator if the voltage is higher - if the voltage is the same - the current will be the same. You reap benefits when the stock unit would have collapsed its output voltage under load - and the higher power unit doesn't and also if you just set the voltage higher.

Now some folks think if they had a higher voltage regulator they would get more current (and more stable voltage) - simple change to make... bolt in a new regulator...!

Well if all else is the same - a higher voltage will inded give you more current but only until you hit the ~same thermal limit in the regulator (which will now happen sooner - due to the higher current you have been pulling = more power dissipated). Then the voltage drop will be likely be higher - all the way down to about where you started out under worst case conditions.

What's needed is either a differently thermally compensated regulator, or a smarter regulator that better manages charge current & voltage. (perhaps better battery sensing for voltage & temp)

You also need to understand that the power dissipated in the recifiers is pretty much directly related to the current level (the voltage across the diodes is close to fixed). So the more current it sources the more power = more heat. The cooling capability can't be improved that much in the same space - so you will need rectifier diodes that can live at much higher temperatures. This is possible to a degree, traded against higher cost, however there is also a tradeoff against lifetime. Super high output in a similar configuration likely means lower operating lifetime before failure. I'd be very surprised if that is not the case here. However most customers probably don't use substantially higher output current than they had before (under most conditions) mitigating this substantially.

Generally a higher nominal output voltage is not really at all beneficial - it can create battery lfe issues, can create reduced lifetime issues on other components - esp headlight bulbs, but also delicate (aged in our case) ECU's...

Jim a remote sensing regulator would certainly be a good improvement - so also would be a remote direct electric fan cooled rectifier pack - keeps them away from the challenging engine temps and low/hot idle arflow . An alternate would be an additional air blower on the shroud intake end as Dr Bob suggested.

Alan

SeanR

Some problems with reading comprehension is apparent in this thread.

I don't know how one gets the impression that he's going to be sitting in a parking lot with his stereo cranked up with the engine idling all day. Not the intention at all on this. This is someone putting his money where his mouth is and doing what every one keeps talking about. Improving an anemic electrical system and not just tossing some junk yard Ford alternator on there and calling it good.

I find it amusing that some of the comments from Alan were addressed even before he posted about it. The alternator is quite smart, it isn't pumping out 15v/270 amps all the time. If the car has everything cranked up, the alternator is meeting the demands of the car. Modern tech meets up with 70's tech. I kinda like it.

Alan

I have seen no answers... maybe you can point them out... What was stated about this alternator suggests it is powerful but not smart - thats what I read on the other post - maintains high voltage even at hot conditions (idle or otherwise). That equates to much less temperature compensation at much higher voltages.

The stock system is a bit over aggressive with its compensation but that is its only charging regulation... now the alternator will maintain a higher than battery float voltage more or less for ever.

This actually isn't a good thing. I don't think it would be so wise for many other folks to spend the money to do exactly the same - expecting its the ultimate solution....

Now the install prep sounds interesting, and well done - the premium alternator also sounds interesting ($$$) - I'd just suggest a lower nominal voltage for reliability.

Alan