Alternator bypass & engine preheater mod

[oldtamiyaphile]

Originally Posted by paulgato

Jyden, thanks, but a Scanguage is one more thing to have to buy and wire in. Changing the display to read km/litre or litres/100km would be free (or cheaper - I'd have to pay $99 for the full version of the VAGCOM software, but I want that anyway as it will enable me to modify other behaviours of the car too, like idle speed and so on.)


And Clifornia98Civic, that's a great tip about the metal jacket for the Odyssey battery, as my engine bay temperatures do get pretty high now that I have an almost 100% grille block. ... If not, then perhaps I am better off trying to improve the heat-shielding capability of the existing VW battery box (with heavy metal foil on the outside for example? ...or by applying that Dynamat stuff?)

On my Fiat I can switch from Metric to UK units in the same menu that sets the clock etc. I'm surprised it's a back to the dealer job for VW. For maximum accuracy, you can't beat an MPGuino. Mine's picked up things that OBD2 scanners missed. It's cheap, though it has to be wired in. SG2 is plug and play or if the cost seems to high look at Ultragauge or an Android app.

My Transporter has the battery compartment walled off from the rest of the engine bay with a rubber seal against the hood and a cool air intake from above the head light. Although it has thermal properties, Dynamat isn't really intended as a heat shield. Unless you have some lying around, get something intended for the purpose like:

Car Builders - Sound Deadener Heat Insulation Car heat Shields : Kool Mat - Extreme heat barrier (fireproof)

[paulgato]

I have an android app - Torque - and it works for some things. It shows coolant temperature with perfect accuracy for example, and I use it for that regularly, as VW have included only an idiot guage on the dash which shows a needle pointing dead-centre at what is marked as "90" at any temp between 75 and 107. (Thanks guys!) But it is really bad at measuring fuel used or mpg or anything like that. It is kind of useful for measuring engine load. I think the problem may be that in the UK OBD2 didn't come out for diesel cars until 2004 (?) so mine is not 100% compatible with these toys. That's another reason I haven't shelled out on one.

And yes, I have some Dynamat lying around. It has quite a thick foil layer on the outside so it might be useful for dissipating heat. I also have some thin (1mm or less?) aluminium sheet lying around, which might be better. That stuff is super-easy to work with as it can be cut with scissors, ...or tin snips anyway. Looking today, it seems that one end of the battery box gets quite hot and the other end stays quite cool. The battery probably doesn't like that as one cell will be much hotter than the others. Better to spread the heat evenly around the battery with metal sheet I guess. I think the problem is mainly heat radiating off the engine block.

[paulgato]

By the way, I just added a link to my fuelly.com log in my signature (thanks for the suggestion Jyden).

If you click on the link you can see graphs over the last six months or so. You can see that my mpg (Imperial) has jumped recently from 'about 70' to 'about 80'. This is at least a 15% improvement, and it coincides with me starting to plug the car in every night. Difficult to tease out exactly how much of that improvement is due to the alternator delete, but I'm guessing I'm getting at least a 10% improvement from the alternator delete, and the other 5% or so is due to a combination of engine pre-heating and the slightly warmer weather, (...although it was an extemely mild winter anyway with virtually no frost.)

[redpoint5]

You have a great idea to eliminate the batteries from under the bonnet. Using an ultracap would allow you to use a thinner gauge of wire to the batteries in the rear. The car should handle better having the weight more evenly distributed.

Failing this, buy a section of Mylar for insulation. It isn't conductive and does a great job at thermal insulation (and is dirt cheap).

I assume the TDI has glowplugs? If so, you could easily over-run the ability of the supercaps to supply them and then start the high compression motor.

[paulgato]

Oh yeah, Mylar. Good thinking redpoint5...

But I just remembered, I was sent a large sample of Tyvek Reflex 'metalised' breathable membrane a while back. That is very tough, as lightweight as paper, electrically safe and completely waterproof. It is supposed to reject 88% of radiant heat, and it certainly works well as a sun-shade. I could cover the existing black plastic battery box with that stuff.

I was going to get an Odyssey starter/deep cycle battery, and the PC1220 is the one that will fit in my car, but I don't think there is a metal jacket available for that model. I'm kind of leaning away from spending megabucks on a really good replacement starter battery like the Odyssey when a supercapacitor array might do a better job and cost less.

Thanks for mentioning the glowplugs. As far as I know this car doesn't use the glowplugs at all above -5 degrees C, and I use an engine preheater anyway, so I would very rarely use the glowplugs. I didn't use them at all last winter as it was so mild. But when you need them, you need them!

I believe the glow plugs use 50A for a few seconds. If my DC/DC converters put out 25A, then after using glow plugs for five seconds, I'd need to wait another 5 seconds for the converter to have fully replaced the energy in the capacitors. But that wait may not even be necessary. The great thing about capacitors is that they still dump huge currents out even when their voltage has dropped. Even at 9v or 10v, a capacitor array can still start an engine. Also they are not affected by cold weather to the degree that lead acid batteries are.

Some people have combined a small, lightweight battery (LiFePo4?) with a small supercapacitor array to increase energy reserves. But in my case it might be cheaper and easier to simply add another DC/DC converter module to increase the current going to the capacitor array from the donor batteries in the rear.

An interesting article here about starting diesel locomotives with supercapacitors charged via DC/DC converters...

http://www.kemet.com/Lists/Technical...capacitors.pdf

And yes, using a DC/DC converter means the current is always safely limited despite the voltage being good, so no fat cables are required. With my single 12A converter I'm currently just using the existing wiring which feeds the 12v rear power outlet. That is fused at 30A. It would be an advantage to run a thicker wire, especially if I add a second converter, as I will be losing a few watts of energy in that thin wire, but it's only really necessary if I add a third converter module as I'll then be putting 36A through it.

I think I could just try the capacitor array with the glowplugs one winter morning by deliberately leaving the engine pre-heater switched off, and if the car doesn't start easily then I could add another DC/DC converter module at that point, but somehow I don't think it would be necessary.

[paulgato]

I just spoke to a technical guy at Enersys in the UK about their Odyssey car batteries.

A longish and useful conversation in many ways, and he was interested enough in the fuel-saving project to take some time over the issue.

(This is often the case in my experience. These deeply knowledgable technical guys sit there all day answering the same old questions from non-techies about standard applications, and when someone has an interesting and novel application for a product they will often take a real interest and put their best thinking cap on to come up with a solution. I love engineers!)

It turns out that no, there is no metal jacket available for the PC1220 battery I wanted to use, and yes, without a metal jacket the maximum ambient temperature for the battery is 40 degrees C, whereas with a metal jacket the Odyssey batteries can operate at 80 degrees C.

But the "Aha!" moment came when he explained why. The metal jacket is NOT a heatshield. It is a mechanical restraint which prevents the battery physically expanding or 'ballooning' when the plastic casing heats up. When that happens the battery plates start to separate and the battery fails. These batteries can cope with high temperatures as long as they are mechanically reinforced.

So, we've been talking/thinking about heat shields and insulation, and that may help to some extent, but the main thing is to physically reinforce the battery casing, especially at the ends. I said to the guy, "So, if I were to put a square aluminium plate at each end of the battery and wrap glass fibre and resin around the whole thing, then that might do the job...?" He said, "That would do it."

[California98Civic]

Originally Posted by paulgato

I said to the guy, "So, if I were to put a square aluminium plate at each end of the battery and wrap glass fibre and resin around the whole thing, then that might do the job...?" He said, "That would do it."

I had learned about the expanding problem during my own long conversations with the Odyssey techs, but this home-remedy never came up. Thanks for that. I have a smaller Odyssey battery I could adapt in this way.

[paulgato]

I've decided not to use glass fibre, just in case I need to return the battery under warranty. But if your battery is out of warranty California98Civic, then the fibreglass would be the easier option.

I phoned a local aluminium fabricator shop and found out how cheap aluminium plate is. They can cut me four rectangular plates - 6mm thick for the battery ends and 3mm thick for the long sides. Gonna cost about £15 total. I have some 3mm thick angle aluminium pieces about 70mm wide left over from a previous project, which just happen to be cut 130mm long, so just perfect for this. I shall epoxy bond and/or bolt those angle bits onto the 3mm thick long-side plates, and then I can slide those three-sided long-side pieces over the thicker end plates, thus holding the battery together securely, end-to-end. A few machine screws will hold the long-side pieces to the end plates, ...but one could equally well use gaffer tape or cable ties, as it is mainly end-to-end expansion we need to worry about.

The tech guy said that although the casing can sometimes expand in the sideways direction, expansion is only usually an issue in the lengthways direction as that is when plates start to separate. He said that the base and the top of the battery don't need reinforcement. In fact he said that when they test batteries at high temperatures they use two metal plates at the ends, clamped together with four threaded rods and nuts, and put the battery in the 'oven' like that to test.

That home-made metal jacket will be fully removeable if I ever need to return the battery under its 3-year warranty, and it is slim enough that the battery will still fit in my existing battery tray/clamp and existing battery box with no modification.

[Edit: Then again, if I use four plates rather than two, then wrapping with glass fibre will not involve glueing anything to the battery itself, so it could all be removed if necessary by cutting through the fibreglass at two corners. Much less work than all that drilling and bolting! Also there would then be no exposed conductive surfaces that could cause shortcircuits.]

[oldtamiyaphile]

I used to work in aluminium, I would use stainless rivets as the quickest way to build such a box. As I read your post I was thinking, since ambient air temps here reach 45C (and under bonnet temps must be approaching 80), I'd just rivet an alloy box together in about 1/2hour, and save the mess of fiberglass. All depends on what you're comfortable with I guess. You could also get powdercoated aluminium to reduce the risk of shorts.

[paulgato]

Yes, I'm not that familiar with using rivets, and I don't have a riveter tool. It sounds like a good and satisfyingly quick process, although I'd be concerned about any protruding rivet heads, especially on the inside, as these plates will potentially be pressing hard against the battery wall. Maybe flush rivets are available?

In general I'm a fan of screwing and glueing (epoxy) for aluminium. The screws clamp the glue joint while it's setting, and then give some security against sudden catastrophic failure in service. If the glue line fails the joint will become loose and visibly wobbly before it gives way completely, and the epoxy prevents those miniscule movements which can cause mechanical joints to work themselves loose or strip threads over time, ...as well as providing a waterproof seal that protects against corrosion. Aluminium doesn't normally corrode if it's out in the open, but if two surfaces are close together - or if a paint layer is broken - then corrosion can happen in between. (This may not apply in sunny Australia or sunny California!)

Fortunately, here in rainy England we don't often need to worry about 45 degree weather! I used to monitor under-bonnet temperatures as I was aggressively blocking my grille even in summer. It was all within acceptable limits except on long drives on summer days when occasionally I would see the under-bonnet air temp creep up past 50 degrees towards 60 degrees, at which point I would stop and pull off some of the foam blocking the grille. Even at those engine bay temps the engine itself was never even close to overheating, and the fan would almost never cut in.

But 50 degrees, yes that's not unusual, and that's too hot for the Odyssey batteries unless they are clamped together in some way. The tech guy I spoke too didn't think that temperature would shorten the life of the (clamped up!) battery significantly, a) because it's not being CHARGED at high temperatures (charged at night from the mains) and b) because those elevated temps only apply while driving, which only accounts for about 5% of the time.