Alternator bypass & engine preheater mod

[paulgato]

Bad news: the replacement alternator self-excites at engine speeds above 1500rpm, turning itself on and not turning off unless I stop the engine and wait for a minute before starting it again. This means I can't disable it.

Well, I could disable it by interrupting the main output cable, but that makes it much more difficult to reconnect it, and much more difficult to arrange an ON/OFF switch for it.

It's a used alternator. Didn't cost much at least. A Bosch. I don't think they're designed to self-excite, so I guess the rotor has developed a degree of permanent magnetism over the years, but I'm only guessing.

[oldtamiyaphile]

What would happen if you ran 15v to it, fooling it into thinking the battery was full? Or something along those lines.

[paulgato]

Originally Posted by oldtamiyaphile

What would happen if you ran 15v to it, fooling it into thinking the battery was full? Or something along those lines.

Yes, well, that was my original idea, way back before I got the DC/DC converter that outputs 14v. A simple solution, and it might just work, but I am where I am with the kit I've already got.

1. I could try to repair the alternator I apparently fried a few weeks ago when I tried to ground the field winding to effect an alternator OFF switch. (I wish I hadn't done that!) I'm really not confident of my ability to repair it though.

2. I could also get another used alternator and hope it doesn't self-excite. The last one didn't.

Or I could take the opportunity to work out a method of switching the alternator both ON and OFF. (With the 'old' alternator I could switch it ON OK, but I failed to find a way to switch it OFF while the engine was running. A proper ON/OFF switch would be cool because then I could wire the alternator in with the brake lights or an inertia switch for regenerative braking.)

A 15v feed ought to switch the alternator off, and switching the 15v feed current off ought set the alternator charging again. I think it would work, if I could get hold of the right kind of DC/DC converter to do the job, but 15v is slightly too high for the Odyssey starter battery. When the starter battery in the engine bay warms up to 40 or 50 degrees C, then 15v would overcharge it badly. Odyssey batteries really don't like being charged above 15v I believe. I think I'm too far down the 14v route to change to 15v now.

3. Another possibility is to put the alternator's +ve output through a high current relay (or solid state relay) with perhaps a 2 ohm bypass resistor so it never switches completely off but cuts down to a couple of amps output in the OFF position. That ought to work with any alternator.

4. Or I could search around and find an alternative alternator which will fit, and which is designed to be switched on and off.

5. Or I could just throw some heavy lead acid batteries at the problem, and have such a large bank of batteries that almost all journies can be completed without the alternator. Then I can disconnect all wires from the alternator and just make sure to carry the tools necessary to reconnect the main output wire if and when it ever becomes necessary. In fact this is probably the simplest option, as I have already made provision for fitting a second 105Ah Yuasa deep cycle battery in the spare wheel well. I wasn't sure I wanted to carry around all that extra weight (another 30kg) but from an electrical point of view it would make for a much better system as the batteries would be well within their comfort zone during normal everyday driving, so should last for years. And on longer journies I should have several hours of alternator-free driving time, even with headlights and/or wipers running. There's bound to be a slight mpg hit from the extra 30kg, but it's a 1500kg car and 30kg is only 2% of 1500kg. I very much doubt the mpg hit would be as much as 1%. Option 3 (above) would probably have a similar mpg hit as the alternator would be producing a couple of amps at all times, and the field winding would be energised at all times.

If anyone has any bright ideas, or can tell me how they managed to disable/re-enable their own alternator, please let me know!

[paulgato]

I think I managed to fix the alternator! And I now have a way to both switch it on and switch if off, although not in a regenerative-braking kind of a way.

This alternator problem was driving me nuts, I have to say. Having destroyed the original, working alternator - which I could disable simply by leaving the ignition feed wire disconnected, and re-enable simply by stopping and plugging the wire back in - I then got another 2nd hand alternator (Bosch) only to find that it self-excited at 1500 rpm, so couldn't be disabled. I hunted around, phoned around, became quite amazed at the lack of good information out there on which alternators self-excite and which don't, and eventually found a guy in an alternator and starter motor re-manufacturing company who was very certain that Bosch alternators sometime DO self-excite, but that the alternative brand for my car, Valeo, NEVER self-excite. They had a reconditioned Valeo on the shelf and I bought it. But, (Arrrgh!) the Valeo also self-excited, and not just at 1500rpm but at ANY engine speed at all, even at 800 rpm tickover. I sent it back and they refunded my money, but so frustrating!

So, really, this was driving me bananas. I read on ecomodders somewhere that a guy had experimented with simply leaving all wires disconnected from his alternator, and his alternator died within weeks. Apparently doing that (with a self-exciting alternator) will drive the voltage up in the alternator to 40v+ as it tries to charge an apparently completely flat battery (wires disconnected = "looks like a flat battery that needs every ounce of power we can produce guys!").

And then I had a stroke of luck - just a couple of days ago. I hadn't been able to identify the original alternator as it was obviously a reconditioned, after-market one and had no numbers or maker's name on it. However, on closer examination, I realised that it looked very similar to the used Bosch alternator I had bought as a first replacement. And in fact, the voltage regulators were interchangeable. So I did some testing, swapped the regulators over, and tada! the old one seemed to be working fine with a different regulator in it. So it looks like the only thing I damaged by shorting one of the wires to ground was the regulator.

(Now I did my testing as far as I could, and I did apply a good dose of logic to the issue, but I STILL don't understand what is going on. As far as I can understand, the symptoms I was getting indicate that at least one main output diode in the rectifier MUST be shot, and yet my substitution results show a completely working alternator - with no symptoms of blown diodes - when I put a good regulator in. So I conclude that despite reading up on alternators online as best I could, I still have not come to understand how they work - at least not the Bosch ones. Not a comfortable state of affairs for my engineering ego, but I can accept it. I now have a working alternator, and the 'repair' only cost me £50 for a used alternator, out of which I was able to steal a good regulator. But man! that was driving me crackers. I have literally lost count of the number of times I have now changed the alternator. I think my neighbours were beginning to think I had some kind of alternator fetish going on. I could quite literally and not metaphorically do it blindfolded now, and it is not a particularly easy job on that Golf TDi.)

So all is good. And a bonus is that on testing to check the old alternator still didn't self excite and would remain OFF with the ignition wire disconnected, I discovered, ...that it actually DOES self-excite, but only at engine speeds over 4000 rpm, which is why I had never noticed it doing so before.

This means that I have no need of a switch and wiring to control it. I can simply leave the ignition wire disconnected permanently, and if battery voltage does ever get dangerously low while driving - to the point where I am nervous about being able to re-start the engine if I switch it off - all I have to do to switch the alternator on is to blip the throttle and rev briefly to 4000 rpm. In normal eco-driving I would never rev that high, so I would never inadvertently switch the alternator on. (The red-line is just 4,500 rpm.) That is just nicely serendipitous. I was due a bit of luck like that.

So, I'm back in business, driving alternator-free full-time again. Just driving around locally the VW dash display is pegged at the maximum it can show, which is 99.9 mpg overall average. I know that display is somewhere between 6% and 10% optimistic, so, well, I'm getting something over 90mpg overall average in reality I guess. That's mostly driving around on short local journies for work with tools in the back, so I'm happy enough with that for the time being. The hot weather helps of course.

I'm also very close to having the 2nd battery and charger, wiring, etc. all finally installed, but that's for another post. I'm currently running the system with, ...but I'll split that into another post, as this one is long enough already...

[California98Civic]

Congrats. You know you're an ecomodder if you will spend weeks learning what none know about alternators in pursuit of a few more mpg! Victory!!

[paulgato]

So, just in the last few days I've been driving around with a dual battery system comprising a 68Ah Odyssey AGM battery in the standard engine bay position, and a 104Ah Yuasa YPC100-12 AGM in the spare wheel well. Both batteries are charged up every night and the rear battery feeds power to the front battery through a 12A DC/DC converter at 14.0v while driving.

I had been testing out this system using a spare 70Ah Bosch car battery instead of the Yuasa with reasonable results, but I have to say I am seriously impressed with the Yuasa YPC100-12 104Ah battery. It seems to pump out power for hours without significantly dropping voltage. The YPC range are designed as deep cycle batteries for traction use, and the thick lead plates show in the weight (30kg).

(When I have all the wiring done and completed in a permanent kind of a way I'll post some pics of it here. It's all a bit messy right now.)

So, my dilemma is the following. I have made provision to fit TWO YPC100-12 batteries in the spare wheel well, either attached separately to two DC/DC converters (one each to give a max of 24A) or else simply in parallel, both feeding the one 12A DC/DC converter, ...or else again, simply in parallel with the starter battery with no DC/DC converters involved.

The DC/DC converter has some real advantages over a direct parallel connection by the way...

1. The current flow is automatically limited to a nice safe 12A, so no need for heavy cables or large high current fuses for safety. Also the fact that 14.0v is available means that a moderate voltage drop across cables is not a big issue, again meaning that the car's existing light guage wiring can be used without problems.
2. Current can only ever flow in one direction - from rear to front.
3. Voltage in the car's main system generally remains quite high, which means headlights, etc. run at close to full power almost all the time.
4. The two batteries are always isolated from each other.
5. This converter automatically reduces output as the donor battery voltage drops, so it limits Depth of Discharge to about 60%, which protects the donor battery from damage.

However, the converter is only 'up to 92%' efficient, so I am losing about 10% in the conversion. I have tested and found that in fact the efficiency is at least 90%, and the modest heat generated by the unit is not a problem in the enclosed space of the spare wheel well. But it would be nice to have a more efficient system. (In fact, even on the hottest day with the car stood for hours in the sun, the temperature in the wheel well - under the load area floor - remains remarkably cool and even. It really is the best possible place in a car to install a battery, ...or to keep your picnic hamper or your road kill I guess. Or even a spare wheel.)

If I had two of the Yuasa batteries I would not need to worry about the 10% efficiency loss.

[Edit: oh no wait - mistake! The conversion loss is worse than that because to produce 12.5A at 14v that corresponds to 14A at 12.5v, so the total draw from the battery in amps is something like 20% higher than the output. In other words, if it is to last the same number of hours as a directly connected battery, a battery using a DC/DC converter will need to be 120Ah instead of 100Ah.]

So, is one rear donor battery enough, or do I add a second Yuasa battery in parallel? The usual rule of thumb with lead acid batteries is, "the more you use, the less you lose". Battery longevity is closely correlated with a low average Depth of Discharge. For everyday local driving use, a single (new) Yuasa is more than enough, especially as the car will be plugged back into the mains for recharging as soon as I get home every evening. But on longer journies both batteries (donor battery and starter battery) could become fairly deeply discharged, and may remain that way overnight at my destination unless wherever I am staying can provide me with overnight mains power to the car. With two rear Yuasa batteries, an overnight stay with no charging facilities would present no problem as the Depth of Discharge will be much lower (20% rather than 40%?) and damaging sulfation is much less likely to occur. So, for example, on a weekend beach trip with no facility for plugging into the mains I should be able to get there and back on one charge without any issues.

The weight of a second Yuasa battery will in theory have a cost in terms of slightly reduced mpg, but since I live and work in a fairly flat area, and since my car is already quite heavy I don't think that extra 30kg is going to cost me very much extra fuel at all. (30kg is less than 2% of the vehicle's total weight, so the maximum theoretical, worst case scenario mpg hit is 2% - and that's if I am climbing hills constantly and never coming down again! - but in practice it's going to be well under 1%.) Also, I'm thinking of long, cold, dark and wet or snowy winter work days with headlights on, windscreen wipers and cabin heater going full blast, and I kind of like the idea of not having to ration my electrical equipment use for the sake of saving the batteries. And, I know that if I ever feel the battery charge is getting low, and especially if it is dark and rainy and horrible out there, I can get a little nervous, and that means I am liable to speed up a bit so as to get home before the voltage drops too low. Overall I think more amp hours is going to be better for mpg as well as for safety and comfort. (Another advantage of having more lead than I absolutely need is that I can safely forget about the regenerative braking idea!)

(More of an issue than the very slight mpg hit from the extra 30kg is that the rear of the car will sit a little lower, and will LOOK laden, which is a concern for me because I keep my work tools in there and the last thing I want is for someone to break in to see if there is anything worth stealing. But I can fit uprated rear springs to this car very, very easily and very cheaply, so that is hardly an issue. In fact I had been thinking of replacing them anyway, partly so the load area always looks empty even when it's full of tools, and partly because the springs creak annoyingly. I had thought the creaking was coming from the (leaking) shock absorbers so had those changed last winter, but no, it's the springs or the spring mounts.)

OK, so I am leaning towards fitting a second Yuasa battery in parallel with the first one. The two might not last TWICE as long (in years) as a single battery, but should last significantly longer. If I lived in a hilly area I might hesitate, but an extra 30kg on the flat isn't going to make much difference.

(Did I mention I was impressed by this Yuasa YPC battery? So far, I'm more impressed than by the Odyssey battery, even though the Odyssey 68Ah battery was £200 and the Yuasa 104Ah battery was only £138. Both are good I guess. Time will tell.)

If anyone has any advice or ideas on this I'd be glad to hear...

[paulgato]

Originally Posted by California98Civic

Congrats. You know you're an ecomodder if you will spend weeks learning what none know about alternators in pursuit of a few more mpg! Victory!!

Yeah, victory - kind of. Temporarily and personally. But it's a shame that it seems there is no easy and universally-applicable way to safely disable an alternator - which means each person has to re-invent an individual solution, more or less.

It seems I was lucky with my first alternator in that it doesn't self-excite at normal engine revs. And lucky that I could repair it.

Some people say you can cut into the field wires inside the alternator - like the wires connecting to the brushes for example, but I can tell you on these Bosch alternators there is no way to do that as the brushes are not replaceable and are permanently fitted inside a sealed plastic moulding which is part of the regulator. Valeo alternators could have their field wires cut into in that way though.

Some people could remove the belt, but many will find that belt also drives essential kit like power steering pumps or even engine water pumps.

Some people will be able to fit an adjustable voltage regulator, and turn it right down to 12.2v or so. Those are available for the slightly earlier (?) Bosch alternators, but not for mine, and not for Valeos or any other make as far as I know, unless your alternator uses an external regulator.

My original idea of using a 15.0v DC/DC converter OUGHT to be universal, and ought to prevent the alternator from putting out any current until the voltage drops. And that ought to be a universal solution that requires no knowledge of alternators and no modification of the car's electrical system in any way.

Converters are not efficient though. And apart from the inherent conversion inefficiency, there is also the fact that 10A at 15v (150w) will actually draw from the battery 12A at 12.5v (150w) PLUS whatever the converter's own power consumption is - say 10%. So to provide 10A at 15.0v will likely take 14A from the battery. (I know that my converter which provides 12.5A at 14v draws a full 15A from the battery at 12.5v.)

[redpoint5]

Originally Posted by paulgato

So, is one rear donor battery enough, or do I add a second Yuasa battery in parallel?...

I know that if I ever feel the battery charge is getting low, and especially if it is dark and rainy and horrible out there, I can get a little nervous, and that means I am liable to speed up a bit so as to get home before the voltage drops too low.

If anyone has any advice or ideas on this I'd be glad to hear...

Since you have a self-exciting alternator, I wouldn't bother expanding your battery capacity. If you get nervous about getting low on charge, or you go on an extended trip, just engage the alternator.

I'm no expert on DC->DC converters, but it seems like running 14v from the converter would have the effect of trying to charge your starter battery. A lead acid battery at near full charge is only 50% efficient at accepting a charge. The same goes for discharge.

[Daox]

I agree with Redpoint5. You really don't need the extra battery. I used to have a 40 mile (65 km) commute, and I did easily with one group deep cycle 24 lead acid battery, no matter if I had headlights, wipers, fan, etc. on it did fine. You have 2x the capacity I did.

[paulgato]

Originally Posted by redpoint5

Since you have a self-exciting alternator, I wouldn't bother expanding your battery capacity. If you get nervous about getting low on charge, or you go on an extended trip, just engage the alternator.

Yeah, you're probably right Redpoint5. If I wanted to go for cross-country mpg records then a second rear battery would be cool, but for daily use - and it's daily use patterns that determine overall fuel use - then I had already calculated that a single rear battery of 100Ah would be about optimum. The trouble is I kind of DO want to go for cross-country mpg records on occasion (he-he!) because it's only on longer journies that the highest possible mpg is achieveable, ...but I'll resist the temptation. (It's bragging rights really - you know, being able to rock up at a friend's place 200 miles away, ask to plug into his house supply, and announce I've averaged over 100mpg on the way there. )

Having made a space for two batteries in the rear, with two clamp-down arrangements, etc. - and having effectively ended up with a couple of 'spare' and 'free' batteries in the course of this process - I could just add a second rear battery when I go on a long trip, but for normal short journies leave it at home to save weight. (Another advantage of using DC/DC converters is that I can drop in ANY 12-ish volt battery to increase capacity, even if it is a different size, age, condition, etc. or even a completely different type, such as gel or LiFePO4, because the batteries can all be completely isolated from each other, and can be charged by different chargers.)

I have, for example, a cheap 90 Ah AGM battery that came with a 4-year warranty and which failed after a few months. It's the one I have now replaced with the Odyssey from another supplier. I don't want another of those cheap AGM's because they don't seem to last, and I can't get a cash refund, but I can return it and get them to send me a good gel battery for example which I can drop in on longer journies.

Originally Posted by redpoint5

I'm no expert on DC->DC converters, but it seems like running 14v from the converter would have the effect of trying to charge your starter battery. A lead acid battery at near full charge is only 50% efficient at accepting a charge. The same goes for discharge.

Yeah, kind of. 14.0v is more like a 'float' voltage than a properly efficient charging voltage. In fact, because when driving there is always a load of at least 6.4A, the actual voltage seen by the starter battery at the moment (may change after fitting a larger cable front to rear) tends to be no higher than about 13.5v, although if I leave the converter active while I'm parked up during the day (which I do sometimes if I know I've been depleting the starter battery more than usual) then when I come back the starter battery voltage will often show 14.0v.

I didn't know about fully-charged lead acid batteries being less efficient than partially charged ones. (Did I understand that right?). Are you saying they are also less efficient on discharge when full? The point of the DC/DC converter is more to prevent the starter battery from being discharged rather than to charge it up. In fact the starter battery is always slightly depleted as it is used for starting the engine, and also for any other peak current demands over and above 12A, such as use of electric window motors, wipers, blower, lights, indicators, etc.

I've deliberately set up the wiring for this system so that I can experiment. I've run (just been doing that today in fact and I'll complete tomorrow) ...I've just run a 35mm2 (2 guage AWG) cable through from rear to front so that I CAN connect rear and front batteries in a direct parallel arrangement, to see if that is more efficient. The current pair of batteries, although of slightly different types (both AGM but the Odyssey is pure lead) OUGHT to live happily together in direct parallel, sharing the same charger, etc. I might find I like running the system like that, in which case I can just use the DC/DC converter on longer trips with a third, drop-in, 'random freebie' battery - just whatever battery I have lying about. On longer trips I won't be carrying my tools in the back so there would be no issue of the rear end sinking low and looking temptingly full. (There's been a spate of thefts of tools from vehicles in my area recently so I worry about these things.)