Current Regulator Needed

do you have fire insurance?

Eh,no? Do you believe I would need that were I to install such a device?

I suppose an ordinary battery charger does have some kind of current limiting device. Could I use that? Does it operate in AC or DC?

I am just thinking aloud her, grateful for any helpful comment.

Now, if the current regulator in a battery charger operates on AC I could find a cheapo inverter from 24 Vdc to 230 Vac. That would safe the money for the Dc transformer. A cheap inverter would obviously only produce chopped AC ie. modified sine wave. Would a battery charger tolerate this?

http://www.victronenergy.com/battery-isolators-and-combiners/argo-diode-battery-isolators/

an inverter thats cheap will provide 110-120V for small loads but will not work electronics or computers

Will it work on an ordinary car battery charger?

All of my desktop and laptop computers run very well off of a modified sine wave inverter. I have a little and cheap 90 watt inverter for the laptop to run in the car and a 1,000 watt inverter/battery charger in the motorhome. The output of the MH inverter is a 'modified' sine wave. Don't know about the 90 watt unit but I suspect is is a modifed sine wave also.

The microwave runs OK off of it although the current draw is incredible.

The electric blanket, however, I am told, will not tolerate the modified sine wave and the controller will melt.

What voltage is the battery bank you are wanting to charge and what is its capacity compared to the 24 volt system?

Well the 'bank' is currently one battery 115 Ah, 12V. Eventually it will be two batteries, so double that. The truck batteries are both 90Ah.

OK, the leisure battery(s) are being charged by a solar panel during sunny days. As I am running a fridge off the leisure battery (consumption about 8Amp at 12Vdc), the discharge rate is quite high, too high to be compensated by the solar panel, especially on overcast days. Therefore I was thinking of charging the leisure battery on demand off the driving batteries, while I am driving. The alternator produces excess current anyway, so it won't capitulate at an extra 10 Amps or so. So I am not planning to permanently charge the leisure battery off the driving batteries. I am aware that there is a loss, especially if I transform it into ac, only to turn it into dc again. That is why I am asking you guys. You might just have a better idea...

All you need is a common 24 volt to 12 volt converter. They are very common and cheap.

eBay has loads of them!

Eventually it will be two batteries, so double that. The truck batteries are both 90Ah.
Then wire both batteries you want to charge in series and charge them both at once.

Hope my understanding is correct that you have two systems

90AH, 24V (2 in series) starting batteries.

115AH 12V Leisure batteries.

One way is to have only one set of batteries, that is Starting batteries.

Add to this 24VDC to 12VDC Converter of 10A output rating. It shall not cost more than 100 US $.

Also add an energy meter to give you warning moment you have drained (or DC current transducer and PLC with automation) to integrate total current drain or AH drained from starting batteries, such that moment your drain exceeds 50% it starts the engine to charge up starting batteries and supply your leisure load.

10A 12V will means your peak leisure load is 120W. This will also save your 1.5 sq mm wire from burning.

Further please note that the voltage drop in 1.5sq mm wire will not let you charge your leisure battery to its capacity resulting in Memory loss of its capacity (hardening of Pb SO4 or sulfation of batteries) - better do not do that.

Other method is:

Use independent batteries for starting and leisure (as you are doing it).

Connect a blocking diode at charging alternator in line to 90AH 24 V DC starting batteries (so that these are not drained).

Buy a 24V to 12V 7A DC to DC converter.

Connect input of Converter to output of Charging alternator.

Connect output of converter to 115AH 12V Batteries (through your 1.5sq mm wire).

As you run the Van your leisure batteries shall be automatically charged. It shall take 15 to 16 hours to charge up fully drained batteries.

By above ways you shall save up to 3 times the fuel in charging up of batteries as charge discharge cycle efficiency of Lead Acid Batteries is around 65% hence first charging Engine batteries and then discharging these in to Leisure batteries is not a Green Solution.

Re: Current regulator needed

All right, the voltage converter restricts the current by design. I have not thought of that. Anyway, I have found something called a constant current source. These are commonly used to regulate LEDs. I could stick one of those in, just to be on the safe side. As it happens, I have installed a 3-wire cable. How about using two of those, connected to a voltage monitoring device, which will operate a relaiy switch, depending on the battery voltage. Should the voltage be too low due to the voltage drop, the third cable, connected to the plus of the charging battery will be disconnected by the relay. This will be likely the case, whenever the engine is off. When I run the engine though, the alternator is charging with a higher voltage, which in turn will turn the relay on and allow the current to flow into the constant current source, form there into the converter and into the leisure battery. Sounds good to me. What do you think?

Now, does such a thing as a voltage monitoring device exist, how is it called and where do I find it?

Google voltage comparator op amp.

I do not know your electronics background. However, the circuits you are asking for are well within the average electronics "nerd" or hobby level. Pretty straight forward. However, if you want "canned" circuits on the cheap, it gets rather messy.

Your 24volt system will easily charge a 12volt system with a PWM chopper buck converter circuit. I would however ensure the 24volt system is charging before enabling your circuits, or you will kill the 24volt battery. This could be done with a voltage comparator circuit watching when your vehicle batteries are above the normal "ignition off" level.

For any home-made-circuit, be sure to supply from a fused circuit so that when the unexpected happens you don't have a fire.

key words "buck converter" "PWM motor control"

sample find:

http://www.ecnmag.com/articles/2009/12/designing-buck-converter

A buck converter is a voltage converter that steps down the voltage in a dc circuit, am I right? Sorry about this, I am in Germany/UK and the terminology here is somewhat different from Canada.

These can be found quite cheaply here, so no problem.

I am now concerned about the voltage control of the charging batteries as well as the leisure battery(s). You mentioned a voltage comparator circuit. What is this and where can I get it? I mean, a charge controller, as used in solar charging systems, has both functions. I would however need two of them, one for each battery (as they are of different voltages) and as they are a little costly I would be looking for cheaper alternatives. Especially as they only need one function each, one for undervoltage protection, one for overvoltage protection. Any ideas?

A "buck" converter is one that will "buck" or hold back against the source -so the ouput could be a lower voltage or a controlled current flow, or a current limited voltage source. You can combine both characteristics so the unit limits the maximum current flow that it will output in attempting to achieve the desired voltage output.

I have never dabbled with PV panels, and the only ones I have examined have been "toys" about 1 square foot. But , the concept of a large array requiring its output to be both current limited and regulated makes sense, so your suggestion that one of these regulators between the 24v vehicle source and the 12v battery seems logical.

The next idea would be if you already have such a regulator for the PV Array, perhaps when it "rains" you could either switch from the PVA and supply the regulator from the vehicle - but that would take careful analysis of the characteristics of the regulator. If that is feasible, then you could perhaps even use 2 large diodes and do a wired OR circuit, one diode in line with the PVA array, one diode from the vehicle, joined at the input of the PVA regulator.

Things are getting complicated. Constant current sources are not needed for lead acid battery charging, and not good for variable loads.

Voltage and current control is already a part of your Van alternator charging system.

With one of the Van's batteries & the additional battery you will have enough capacity to run all "leisure" items for at least 12 hours, probably more, as the fridge would switch on / off.

What ever you decide to do, please make sure the connecting cables are of sufficient cross sectional area to handle the load current. A quick blow fuse would also be a good idea.

What do you mean by variable loads? The load is not variable, far from it. I mean, that is the sole reason why I want to install a constant energy source. Just one extra security to ensure that I don't overload the circuit by definitely just taking 8 Amps and no more from the charging batteries.And once it is ensured that the load is always just 8 Amps, by means of a fuse, a constant energy source and a voltage converter, I shoild be very much on the safe side with 1.5mm square, don't you think?

However, I would need devices to monitor the charging batteries, to ensure that they don't discharge too low, and also for the leisure battery(s), to ensure that they don't get overcharged. I have got a charge controller for my solar panels, which has got both functions. They are a little costly, especially as I would need two of them, one for each battery. Are there any devices with a single function, one to protect from undervoltage, one from overcharging, which are a little cheaper? How are they called and where can I get them?

If you are using this to run a refrigerator, TV etc then you should not consider it as a constant current load- even though they may be drawing more or less the same current always.

Constant current sources normally vary the output voltage to maintain a fixed value of current.

Can you tell us the type of load ? we may be able to better understand your requirement.

"As the van operates at 24 volts" ??

My F350 truck has 2 batteries, but I am only at 12 because they are in parallel.

What make is your van? I am curious as to what make/model is using 24volts.

Many years ago I made a small chopper circuit that reduced the 12vdc vehicle voltage to 6 volts rms to operate a glow pulg on a VW gas heater. A similar circuit could be used. (I used a 555 timer to make a 10khz pwm chopping frequency and ferrite chokes and a capacitors to smooth the ripple current on both the input and the output. Adjusted the duty cycle until I measured the 6vrms with a true rms meter. With some additional amplifiers you could measure the current and adjust the duty cycle for the current required.)

It is a Mercedes 709, slightly ancient as manufactured in 1988. 353000 kilometers and still going strong...well as strong as a 90 HP engine can go pushing 6 1/2 tons along. It is rather a light truck than a van, made in Germany and driven in UK for most of it's life.

Again, the question is what is the vehicle starting and charging system voltage? A simple current limiter is a circuit breaker. I had truck that had an alternator that was 12 volts and a starter that was 24 volt. The three AC taps were fed to a transformer unit that upped the voltage to 24 volts to charge the second battery for the starter.(12 to 24 volts) The 24 volt output line from the transformer had a simple 20 amp auto resetting circuit breaker. The entire truck was 12 volt with the exception of the starter and starter solenoid that were fed by the 24 volt terminal of the battery pack. That system was made by Leese Neville. Another option is to piggyback another alternator to the existing 24 volt alternator. Just use a extra groove pulley on the existing alternator and run a belt between the two alternators. All the charging you could ever need for the current or future needs.

Electric controllers used for RC cars, boats and planes may help you further....they can handle surprisingly large currents.

Since you have a 24 V system, you probably have 2 x 12 V batteries in series for the van electrical system.

You can connect "one" battery to your leisure battery.All batteries will be charged when the engine is running.

Effectively you will have 2 batteries in parallel for your leisure load. Switch the battery ( from the 24 V system when voltage drops.)

For interconnecting the batteries - buy jumper leads. Do'not use 1.5 sq mm wires.

( if you do, sleep with the door open you may be able run out when the wiring catches fire ). Calculate a maximum of 1000 amps / sq. inch.

You can install the battery close to the existing batteries so that the cable can be short, but space...and the cable can be small dia as per the load requirements.

Gajanan Phadte

I doubt the van "operates" at 24 volts. some trucks have 24 volt starters but a 12 volt system. 2 batteries in paralell except a heavy relay/contactor to switch from paralell to series for starting. You could add another 12 volt alternator for the liesure batteries or, depending on the existing alternator setup, add isolation diodes off the alternator battery terminal feeding vehicle and liesure batteries separately to keep the vehicle batteries from discharging when not being driven.

It is a light truck, rather than a van. A Mercedes 709, made in Germany, possibly never been imported to North America. Believe me, everything is 24V, I had to get a voltage converter to operate the 12V radio and the fridge off the charging system.

Sounds to me like you already have you 24 to 12 down converter. You just need to repurpose it a bit.

Personally I think you are over complicating what should be a simple off the shelf system.

They make them... http://www.powerstream.com/DCC-2412.htm

Another choice is to exchange your single voltage/single output alternator for a dual output unit.

My motorhome has a dual output alternator that supplies 70 amps to the chassis batteries and 70 amps to the coach batteries (2 X 6 volt 225 amp-hour Trojans).

The charging wire to your coach batteries is entirely too small and you will cause a fire at some point. You should be using very heavy wire, something at least like the battery cables used in a 6 volt system.

A good place to find this wire and the connectors is at a car stereo installation shop. They also build systems with multiple batteries because the car battery is sometimes not sufficient to run their stereos. They probably have two-output alternators available. Believe me, the place to save money is NOT in the battery wiring.

On my motorhome, there is an isolation relay (rotary) that will isolate each battery system. There is a third, momentary relay that will connect the chassis and coach batteries together if the engine needs an extra starting boost because the chassis battery will not deliver enough current (as when it is very cold outside or the chassis batteries have been drained) When the Chassis battery is isolated, it opens the circuit between the battery and the entire chassis (starter motor, driving lights, etc.) and with the momentary relay. The other side of the momentary relay has a heavy wire to the coach batteries. So with both isolation relays closed, if I push the Start Boost button on the dashboard, the momentary relay parallels the two battery systems.

The whole point of dual batteries in a RV is to prevent draining the chassis battery to the point you cannot get the vehicle to start.

You can't regulate current, you can only regulate voltage. This may be helpful in your search.

I would use a voltage regulator as was used on vehicles with a generator.

Adjust the "cut-out" to make the connection to the camper batteries at 13 volt and the current bobbin to 10 Amp. This way current will only flow to the camper batteries when the voltage of the vehicle charging system is higher than 13v. The cut-out will prevent current flowing back to the cars batteries [It works like a diode]

I have not done this but it should work.

There is a simple method, already mentioned by someone, that is to parallel the single battery with one of the two series batteries (supplying 24 volts)....

Also already mentioned, if at least one diode, large enough to carry the worst case current flow, is used to prevent back feeding, it will just get the battery charged by the vehicle's alternator, but not discharged by the vehicle....a fuse might also be a good idea - just in case! Heavy duty wiring is also needed.

The battery will not be 100% fully charged (which I see as a good thing personally!) due to around 0.6v loss when using a silicon diode....In fact I personally would add two diodes in series to drop the applied voltage by around 1.2 volts.....you would end up with a battery not being charged much above 70% capacity, but also not gassing either.....safer!!!

Also, the battery will usually have a far longer lifespan between replacements.....though this also relies on original quality as well as any previous usage.....

Buying one with a 30% larger capacity will sort out the fact that it will not be fully charged if the capacity is important....

A simple method means that it is easily understood and also less likely to go wrong!!!

It would not be difficult to drop the 24 volts and use it to charge the third battery electronically, but it would be more complicated and open to failure.....

A possible simple method here would be to use a 12 volt light bulb in series with the third battery, the higher the wattage, the higher the charging current. It works basically as a resistor, the lower the resistance, the higher the current.....

Never ever tried it myself, but you would still need the diode to prevent back feeding, but even this could be replaced with a relay working off one of the pins of the alternator that basically monitors the alternator output, no signal = drop the relay.....the bulb, when lit, would be an indicator of charging or not.

I forget which pin but if I remember correctly it is chassis ground when the engine is running and plus voltage when not......so connecting a 24 volt relay between 24 volt battery plus and that pin would only connect the third battery when the engine is running....

It is basically the pin that drives the red ignition lamp behind the steering wheel that show red if the alternator is not charging, but goes out when the engine is running.....

My apologies if I have not made it very clear, anyone requiring more infos, just ask.....

Charging a deep cycle battery (or any battery for that matter) to 70% is not a good idea if you want a long life. What you don't want to do is discharge it very much below 70%.

Good charging systems have 3 levels of charge, at the end, when nearly fully charged, the charging system should go into 'Float Mode' to keep the batteries topped up but not boil off the water.

To really get the maximum life out of your batteries, you need to equalize them from time-to-time as well.

Go here to learn a bit more:

http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

We took great care with the batteries on the submarine for good reason.

Actually, I have a battery for my caravan that I bought either in 2000 or 2001, that is still going strong. I charge to around 13.4 volts, then stop charging till it drops to 12.6 (which is the onset of sulphation according to some battery makers), then recharge to 13.4 volts.....

It is a leisure type which helps further......but the charging cycles I use should be good for a car battery as well....another plus is that you can as good as ignore temperature....within reason of course.

Sulphation is basically a question of how long a battery is left UNDER 12.6 volts.....with a car for example, most are recharged a few seconds later - little damage......

Causing gassing is to my mind a great problem for batter life.....once you go above 70% capacity, gassing starts....

But that is just my opinion. You do your thing and I will do mine......

If my caravan battery died tomorrow, it would still have been a relatively long life.....there have been older ones, but seldom in my experience.