Parallel Alterntors for faster charge.

I contribute to a british canal boat forum and they have gone to 26 pages on how to paralled alternators .

What they do is use 50 mm2 cable between the batteries and the alternator to up the baulk current and when the starting battery is charged they connect it and its alternator to the bank . Charge currents are generally doubled ( but be aware that over 25 A per 100AH will heat the batteries ) These boats typically have a 100ah starting and 4x 100ah for the house battery ..

The problem that has taken 26 pages to NOT sort out is that when the start battery is joined to the house battery its voltage drops and the contactor chatters ..In this circuit when the start battery reaches say 14.2v set by the vr the zener conducts and charges the capacitor .this then discharges through the Unijunction and triggers the SCR which switches the contactor .The SCR will not switch off until the ignition is turned off ...and that was another of their problems making it auto reset . If you are clever enough to make it you are clever enough to make some mods.....have fun. Yes I know I missed the earth off the central block of electronics ....yes and alternators has 2 As

 

I did it differently, by use of a comparator and using a zener to set the referance voltage, out of comparator to an opto coupler which turned on hard to drive the relay. I like your way though, it is simpler and less components.

 

Seeing as you invited me over here to continue this discussion...

Nope, that's wrong. The problem that has taken 26 pages to not sort out (whilst veering off into all sorts of wonderful diversions) is how to stop the parallelling once the domestic batteries have reached acceptance stage in order to avoid excessive gassing of the start battery.

Once again, no. In this circuit the contactor will close almost instantaneously and might just as well be connected directly to the engine electrics - it serves no purpose and won't disconnect the engine start battery when it needs to be disconnected.

Regards,
Tony

 

So what your are saying it has taken 26 pages because the peole do not know there batteries properly. Perhaps you do not understand your Unijunctions. Certainly the circuit does what it claims to do ..fires a SCR when start battery reaches a pre determined voltage ..ie is charged
The starting battery will not gas if its voltage is not allowed to go over 14.7v . so there is no point in disconnecting it from a gassing point of view . However when the start battery connects to the well discharged house bank it will discharge into it as the housebank is at a lower voltage.....you just need two solenoids one to disconnect the start and one to connect the house ....but watch how you do your switching it as alterntors should not be run disconnected .

In my experience the start battery takes only a few seconds to replenish the 0.008 AH (100a for 10 sec) used for starting ...the system will not parallel until the start battery reaches the voltage that has been set by VR

Perhaps the attached photo is the real solution ..!!

 

There is a relationship between the size alternator (in this case alternatorS) that is required to charge a specific size battery (or batteries in parallel).

To be honest, any specific battery can only charge so fast up to it's regulating voltage which is usually fairly quick since an alternator can pump quite a bit of amps, from there on the battery will draw the current it requires depending on how much charge it needs.

The only reason I can think of for using so many alternators in parallel (good grief) is if you have some application that does require continuous big currents, like a big beer fridge or something sensable...

 

I only put the 4 alternator on as a joke ..but these canal boat guys have to run the engine 6-8 hrs a day even if tied up as the 400ah of battery does take time to charge after a night watching the telly running pumps etc..if they can reduce this time it saves on engine and diesel fuel

 

Expensive Tv ! For a moment there I was wondering what people did before Tv but it occured to me back then they all had anything from 6 to 27 kids, so yes the canal boat guys save a fortune running those alternators. Just thinking about it, if I was a canal boat guy I'd run that telly 24/7

 

If you have a automatic regulator then when it sees 13.8 it will tail off the charge as it is supposed to do. It doe'snt matter if you got 6 alternators they will all see13.8.

The current from an alternator is exited by the current crossing the slip rings. This can be controlled manually to boost the charge output regardless.

On some auto regs there is a sensing wire that senses the voltage , I have cut his and fitted a rehostat that fooled the reg in to thinking the batt voltage was low. I was then in charge of the output without the heavier gear required directly controlling to current across the slip rings exiter circuit.

Is'nt that right Pistn?

 

Which would be pretty much instantaneous as I've already stated. Just replace your circuit with a switch.

You show not only a stunning lack of reading ability but also a staggering ignorance of battery technology. If you want to boil your batteries then fine, go ahead - why don't you rename your circuit "Battery Boiler".

It's probably a waste of time, because you've already demonstrated that you can't read a thread, but if by some chance you do want to fully understand why you are wrong you might want to take some time to read the technical sections of this site.

Regards,
Tony

 

Davej, please put up your circuit, in the spirit of "more ideas is better"!

With a comparator, you can add some positive feed back to create some 'hysteresis' or 'different thresholds for on and off', and solve the 'chatter' problem with the relay ...

 

Hi terry. Here's a simple circuit that should work fine, PLUS incorporate the most important feature of un-parallelling once the domestic batteries get into acceptance to avoid excessive gassing of the engine start battery.



Note that this circuit is currently untested but there's no reason to believe it won't work as required.

Note also that the only purpose for doing this is to enable the domestic bank to get up to acceptance voltage faster; once they're into acceptance then you only need a comparatively small charge current (for a long period of time) to fully charge them. Most folks never achieve full charge because it takes several hours on a large bank.

Switching the parallelling ON at a certain voltage isn't important in the application this is designed for (narrow boats), it can switch on instantaneously if you wish (which is what Pistn's circuit would do). It's switching OFF when required that's important.

Oh, and there was no problem with "chatter from the relay" in this application - that quote was another result of Pistn's inability to read a thread. Also, 50mm sq cable from alternator to battery would only be on a relatively small installation. Larger boats would have more like 120mm cable.

Regards,
Tony

 

There is a lot of disinformation and old wives tales on the net about battery charging, and this is a good example.

It's absolute rubbish to state that a (12V) battery will not gas if kept 14.7 volts and it is the kind of comment that could only be made by someone who's never actually studied the subject. It doesn't matter if 1000 web sources state the same, all it would mean is that 1000 web sources are all wrong.

The gassing voltage of a wet cell battery is an inverse function of the state of charge. The average gassing voltage of a 12V battery throughout the range 50% to 100% is 14.4 volts. That is a FACT, not an opinion.

I came to this forum at Pistnbroke's invitation partly in an attempt to help clear up such fallacies.

Regards,
Tony

 

As to never studying the subject I use to lecture a 30 hr course on battery testing , maintanence and charging ...alslo lectured on canal boat wiring to the employees of some of the companies who now produce fancy chargers ....as for qualifications both practical and technical I got shedloads .

In the old days of dynamos you raised the battery volts to 15.3v but had to top up the battery every week as it gassed . With increasing maintanence intervals the makers reduced this voltage to 14.4v (14.7 in japan) to prevent gassing and hence loss of water . This resulted in the battery only being 80% charged relative to the old dynamo 15.3v days.

Sure the start battey will be charged fast its only supplied 0.008 ah to start the engine ....(100A for 10 sec )

Sorry dont see what D1 is for as the output from W is half wave recifed AC anyway (relative to earth )and a reverse current cannot flow back into the alternator ..or maybe you did not know that ....ha ha... are you trying to say the voltage at W falls when the start battery is charged and the relay drops out ...??? dont think so ..1watt thin filament bulb ,thats a reliable component ...perhaps if we could see the alternators /contactor connections and the batteries is might make some sense ......????

An explanation of the circuit is required with a fuller diagram ...

 

Attached is the circuit, as i'm writing this from work, i trying to remember the circuit from memory, and thus no resistor values.

This idea of the circuit is to sence the charging voltage on the battery. The zener is used to set the referance voltage for the comparator, if the charge voltage rises above the referance voltage it start to provide current to the optic relay, which turns on hard when enough current to turn it on.

The Variable resistor on top of the comparator are your offset, your adjustment to how much of a difference between the two voltages to when to turns on the optic relay. You could also add a time cct between the optic relay and the comparator to build in a time delay to stop relay chatter, most likely a 1-2 sec delay.

I used a 5v regualtor to power the comparator, but i believe it can work up to 16V or maybe more so is not realy required.

I had this device working great on the breadboard hooked up to me desktop power supply, but when i soldered onto a board and put it into the car it would turn on all the time, quick testing showed that the zener referance voltage was at 11.90 V when i needed it to be around 12 V, the offset didn't have enough adjustment to compensate, i could shove a normal diode under the zener to bring up the voltage, or change the resistors value for the offset.

The capacitors are just for filtering any spikes, these IC's are analog devices so can handle noisey power supplies, but it is good practise to always filter them.

The Comparator is a LM311 and the optic relay is HFS2A213DN, both from jaycar. I haven't done anymore work on this device as i've been too busy so will be interested if anyone can clean the design up some. I'm not sold on the use of voltage refeance and will look at current sensing in the future, as i would like to control the current and direct it where i want it to go.

Dave

 

I think you picked too high a voltage for the Zenner dave...you dont want the have a 14v zenner but a lower say 4.7v and a potential divider....what you have done dave is produce a VSR voltage sensitive relay without the capacitors timing to stop the chatter ...VSR often lock on for 20 sec once activated to stop cycling chatter...If you want to stop chatter there can be no substitute for an SCR..if its on it stays on ..

What some of these canal boys are doing is fitting an external regulator set higher than 14.4 ..if its connected too long the battery gasses and the plates get blown apart by the gas ..bad idea .acid goes pink with bits of disintegrated plate material...what they forget is below 14.4v the switching transistor in the Alt Volt reg is on so you have full rotor current ...Alternator output current is determined by cables and state of battery....current drops as battery voltage rises and then at 14.4v the reg prevents furthur rise in output voltage to prevent gassing

Used one of your comparitor chips a long time ago to clean up signals from the first Russian Satellites ..worked great until they coded it !!! Great weather for us dave ..not rained for 5 weeks now ....