Battery charging - howto?

[Farrari 4]

I, like most others, have dual batteries. One 125A/H deep cycle house and one smaller wet cell start battery along with a single 60A alternator. The configuration I have at the moment uses diodes along with a smart charger with the sense wired on the start battery.

 

I suspect that my house battery is not getting fully charged, either that or I am drawing significantly more power than my calculations allow for. In my last two handed the house battery voltage dipped below 12V at around midnight so I had to start the noisy smelly thing. What's worse is that the new flash 19" DVD player I bought the wife to seal the upgrade in boat size won't last a full movie

 

My question is - has anyone had a good experience with series regulation like the duo charging system as an alternate to installing a second alternator? Is there a smarter way to charge the house battery so it reaches full capacity?

 

Here is a system I was considering if it works.

 

 

[Jon 360]

Yep been down this track.

I had a smart charger and a VSR but ended up ditching the lot as the VSR would link the engine battery to the 2 house batteries when it reached a set voltage but as soon as they were joined the voltage combined would drop them out again, the problem was that the banks were of dissimilar size and to make it work I would have had to charge the house before the motor bank which I never thought sound practice.

 

So I now just feed a relay off a terminal on the alternator that only becomes live when the alt is charging, this relay feeds a solenoid that links all batteries into one bank, works great and really simple

I also use a 60w solar panel to top off the house batteries when on the marina

 

Ps, I also feed the fridge compressor off this relay so it only comes on once the engine is running and also you can't leave a coil on the compressor running.

[wheels 543]

Before I answer Ferrari, Danaide, just beware that the only way you can link all batteries to make them one bank is if all batteries are identical in type, size and age. Otherwise you will find unequal charging. Also you have to be very careful that one battery in your bank does not end up at an major unequal voltage state, because they won't charge equaly.

 

Personally, I do not like those VSR's because they don't allow the banks to ever come to full charge. The proper use for them is as a Bank disconnect device to ensure you start bank is disconnected before it ever gets too flat. Using them as a charge switch is an expensive waste of time.

 

Ferrari, the best way to charge them is similar to what you already have. But a small mod is required. But to go back one step first.

Is the house bank a real deepcycle battery, or what is called a "traction" battery?

Secondly, 120Ahrs, is not alot. Cycling to 12V will mean you are only getting 60Ahrs of actual usable energy.

Thirdly, when you are using a load drawing a current from the battery and the Volt meter is showing 12V, you can actually keep going. While under a current draw, you can drop the voltage down to 10.5V. It is the Voltage measured at no load that can not be less than 12V.

Righty, so if all the above checks as good, then you have a few other options. First is, if you are using one of the older Diode charge splitters, you need to biff the usless things over the shoulder and seeing as we are in a "Green world" now, over the shoulder with a rubbish bin behind you. A Diode has a voltage loss of 0.7V across it. Seeing as the difference between full charge and flat for a battery is just 0.6V, then you are not actually fully charging the banks. The Alt will be producing 13.8V most likely. But after the splitter, you only get 13.1V and that is not enough to get the Bank to a good full or even fast charge. The new generation splitters are FET's and have no loss at all. And they are not hugely expensive. About $120 I would expect.

Another choice is to fool the Alternator sense circuit. This is a little more difficult to do, unless you have an adjustable regulator. There are add on uints that you can buy, that give those options, but tend to be expensive. However you can place something in the sense line to drop the voltage and trick the ALt to give more Voltage. However, that doesn't solve the charger problem.

The only other thing you can do is get a charger with two outputs. I have seen a few on Trademe just lately for $200 approx.

[shanson 0]

Hey Wheels

 

Do you have more info as to why those VSR's aren;t that good? I used one on my previous boat and it seems to be great. I had 1 cranking battery and 1 house.

 

Also, I'm looking at re-doing the charging/battery's on the new boat, I was thinking about using a VSR to separate the single cranking battery from the 2 X 110amp hour house battery's.

 

I plan to have 2 X 40watt solar panels and currently have 1 X 65AH alternator.

 

In the last boat they all fed into a charging loop, through the VSR to the battery's. In your opinion what would be a good solid cost effective (!) Set-up?

 

Cheers

 

SHANE

[wheels 543]

o you have more info as to why those VSR's aren;t that good?

It is not that they are not any good as in itself. But in how it operates. The VSR stands for Voltage sensitive relay. They have a trigger Voltage. So once the battery being switched out of circuit reaches that trigger voltage, the relay switches the battery out of the charge circuit. So it never gets to see a full charge. If you have cheap n nasty start batteries you don't mind replacing every few years, not a problem. But a big Diesel needs a good start battery and that means expensive and I like making mine last.

On one hand I have a complex set up, but at the same time I have kept it simple. I simply have a FET charge splitter and the Alt, Battery Charger, Solar Panels and Wind Gen after they have been regulated all go through that splitter and charge both banks to what they require as they require.

Originally the VSR was made to be a safety device to stop the start bank from ever being discharged below a safe starting point. But it seems to have crept into the use that you guys are now taling about, where it allows charge to enter the Bank and then once it reaches a srt point, it switches that bank out. Or another setup is to switch the Alt/chg from one bank across to the other. But same issue with the trigger voltage.

[shanson 0]

Thanks Wheels

 

what is this FET battery charge splitter you speak of?

 

Did you buy a commercial unit or make one yourself?

 

Cheers

 

SHANE

[Farrari 4]

Righty, so if all the above checks as good, then you have a few other options. First is, if you are using one of the older Diode charge splitters, you need to biff the usless things over the shoulder and seeing as we are in a "Green world" now, over the shoulder with a rubbish bin behind you. A Diode has a voltage loss of 0.7V across it. Seeing as the difference between full charge and flat for a battery is just 0.6V, then you are not actually fully charging the banks.

 

Thanks Wheels. My smart charger has been tweaked to take into account of the 0.7v drop. It is one of those three stage chargers so puts the bulk charge in somewhere near 14.5V + 0.7V. I know the MOSFETs are the new world but I figure the losses through the diodes are minimal (heat mainly). Perhaps I'm wrong there. I am interested in your 10.5v comment though. I always understood that 50% capacity was the threshold before damage to a deep cycle battery would occur and this related to approx 12.2V unloaded. I don't understand what the internal resistance of the battery would be to work out what this relates too under load but figured anything shy of 12V was starting to get dodgy, but again I have no real world experience to back this up.

 

My biggest concern is that the battery voltage sense for the smart charger is wired off the start battery. I am assuming that this means the bulk charge is going to get cut short because the smaller start battery is going to be fully charged relatively quickly while the house is still under cooked.

 

Danaide, I too am not keen on using a VSR but for a different reason that Wheels alluded too. The batteries are very unequal and I suspect it would cause long term damage to one or other. I actually have a manual bridging override 1/2/both switch that I can use in emergencies if required.

 

I like the idea of a series regulator as it will in theory charge both batteries using three stages independently to 100%. I actually like the idea of having two separate alternators better but this is kinda expensive and would take a lot of re-engineering work. According to Nigel Calder's book the only downside to series regulation is that the house requires sufficient charge before the start regulator can kick in.

 

At this point this is all theory. Has anyone used series regulation successfully or am I barking up the wrong tree?

[wheels 543]

My smart charger has been tweaked to take into account of the 0.7v drop. It is one of those three stage chargers

Excellent.

Diodes are different from Resistors. A resistor "resist" the passing of current and thus the loss is given off as heat. A diode is more like a "switch" in some respects, that takes a certian level of voltage before it "triggers" and starts to conduct. It does not have a resistance to current flow, outside of it's normal conduction losses, which is small.

I always understood that 50% capacity was the threshold before damage to a deep cycle battery would occur and this related to approx 12.2V unloaded.

It's complicated and is what actually determins the difference between a start battery and a deep cycle battery. A start battery can give up its current quickly, so turning a high current demand starter or winch motor is what it is designed for. But it does not tolerate deep discharge. A deep cycle battery is slow at giving up current, but it will give a current over a longer period consistantly.

All Flooded Lead Acid (FLA) batteries will start to deteriorate as soon as the charge starts to drop below 12.4V. The lower the voltage they aquire, the faster the sulfation rate.

Because a deep cycle gives up it's current slowly, the Voltage actually drops further while under load than in reality what it has actually given up. All battery measurements should be undertaken after an hr or two under no load. You will notice that if you switch off anyloads, the battery voltage will slowly rise again. The same applies the opposite way also. Charging volatges will be high just after charging and the best most accurate time of measuring the condition of a battery is with no load and no charge after a 24hr rest period.

 

I would switch that sense wire over to the House bank, but monitor you start bank that it is not being over charged.

 

Shane, i bought a splitter. I will see if I can find the name of it and post it here.

[Rafin 2]

We've got an electric frig. and were always having a flat house battery with conventional Yanmar 50amp alternator and a VSR that gave the start battery priority. Eventually (after much experimenting) fitted another house battery for more storage capacity, added a 90amp alternator I got off trademe for $30, fitted an off/on-individually/on-all-together battery isolating switch and removed the VSR. System now works well and gives us the back-up of being able to connect all 3 batteries together via the isolating switch and use one alternator if one fails.

Things we learned along the way; one b section belt won't drive a 90 amp alternator for long, we didn't have room for 2 belts so now use the original poly V pulley, fitted a pulley from a power steering pump to front of crankshaft and bought a $30 belt from Repco.

Leaving the VSR in the circuit resulted in the original 50amp alternator shutting down as soon as the 90 amp kicked in so I removed the VSR. Now we have 2 independent circuits and total of 140amps charging ability.

A 27hp Yanmar stalls when cold driving both alts at low revs., 140 amps needs around 2.25 hp. When batteries are down we start the engine at idle and the 90amp alt doesn't charge, gun it to about half throttle and the 90amp alt kicks in, after only a few seconds engine is warm enough to return to idle and drive both alternators and engage transmission.

It is helpful having an engineer on the crew too! However the engineering work was relatively simple. The alternator is mounted on an extension of the front port engine mount and everything can be easily unbolted. We've done about 200 hours in the year since this was finished and it seems to work fine.

[Guest]

Excellent thread and some great advice from Wheels, but I just wanted to "amplify" on a couple of his points which I don't think are quite correct.

Diodes are different from Resistors. A resistor "resist" the passing of current and thus the loss is given off as heat. A diode is more like a "switch" in some respects, that takes a certian level of voltage before it "triggers" and starts to conduct. It does not have a resistance to current flow, outside of it's normal conduction losses, which is small.

Once a diode is conducting in its forward direction it is EXACTLY like a resistor. A typical diode used in a charging setup has a voltage drop of 0.7 volts as already mentioned, so if you were charging at say 50 amps the power dissipated in the diode is given by P=IE i.e. amps times voltage so it would be 50 * 0.7 = 35 watts in this case. There is only one place for this wasted power to go and that is as heat. So diodes used in any application must have the correct rating to be able to dissipate the heat generated - this is called the maximum total dissipation. Sometimes heat sinks are used to allow the diode to dissipate more heat. So you are losing some of your alternator output as heat through the diode with a simple setup like this. As Wheels say, a diode is like a switch, but perhaps more like a one-way valve - it conducts current in one direction only.

 

Secondly, 120Ahrs, is not alot. Cycling to 12V will mean you are only getting 60Ahrs of actual usable energy.

Thirdly, when you are using a load drawing a current from the battery and the Volt meter is showing 12V, you can actually keep going. While under a current draw, you can drop the voltage down to 10.5V. It is the Voltage measured at no load that can not be less than 12V.

Wheels is dead right about the no load voltage being the way to measure the true discharge level. But to suggest that you could have a voltage of 10.5V under load in the situations we are talking about is optimistic. A start battery will drop to between 9.5 and 11V while cranking the starter, but that is drawing anywhere from 100 to 500 amps depending on the motor. Our Yanmar 4JH4-TE (75hp) starter motor has an initial current draw of 450 amps when starting, dropping to about 250 amps and 10.5V once the starter has the engine rotating. If you take your deep cycle or traction house battery to anywhere near 10.5V under typical house loads of 10 to 20 amps max, you will kill it with sulphation in no time. The standard table of no load battery voltage vs available capacity goes like this:

100% 12.6 to 12.7V

75% 12.4V

50% 12.2V

25% 12.0V

discharged 11.8V

 

At typical house loads (say 10 amps for example) on a traction battery of 120 Ahr capacity you will see a loaded voltage at the battery of around 0.2V to 0.3V less than the no load voltage. Discharging to 12.0V under typical load would mean about 12.2V at rest which is around 50% discharged which is a good compromise of usable capacity vs length of battery life.

 

Cheers

Pete

[Guest]

Wheels - re the VSR's I have one in its box that came with Energy (see attached pic) that the previous owner was going to use for the solar regulator. Panel is 15 w onto a single 200A/hr gel acid (no start bank as its an 8hp outboard + charger and is pull start) Cut in is 13.7V cut out is 12.8V.

 

Wrong application (?) and should I bin/sell it and get a specialist charge regulator/solar charger? I have a diode in-line on the + to stop discharge at night.

 

Thoughts appreciated.

[Farrari 4]

EE, my understanding of a VSR is that it will connect two batteries together when the voltage rises beyond a threshold (i.e. under charge). It is intended to connect two batteries together when charging and disconnect them when not to protect the start battery. It doesn't sound like this is what you are trying to achieve.

 

I have seen a couple of other good threads around here on solar charging. It might be worth while doing a search.

[Farrari 4]

At typical house loads (say 10 amps for example) on a traction battery of 120 Ahr capacity you will see a loaded voltage at the battery of around 0.2V to 0.3V less than the no load voltage. Discharging to 12.0V under typical load would mean about 12.2V at rest which is around 50% discharged which is a good compromise of usable capacity vs length of battery life.

 

Thanks Pete.

 

My current arrangement leads me to believe that the bulk charge phase will be shortened due to the smartcharge regulator sense being wired on the start battery, the end result being a longer time to charge the house battery (more motor time ). If I shift the sense to the house I would highly suspect that I will overcharge the start battery and shorten its life considerably.

 

Are there any other options I could consider in lieu of installing a second alternator?

[Guest]

Not sure how big your engine is Farrari - maybe 30 to 40hp if it has a 60 amp alternator? We've gone the dual alternator path with the standard internally regulated 80A alternator that comes with the engine and a second 120A with external smart regulation. The first charges the start battery and the second the house bank (440 Ahr - 4 x 6V traction batteries). But I know there is a lot of work in fitting the second alternator (although the bigger Yanmars come with mount points for a second alternator as standard - you need to get or make brackets though). I favour this system for redundancy as well as solving all the issues that are the basis of this thread. If one alternator or regulator fails you can simply run on the "both" switch until you get the problem sorted (with a bit of unequal charging etc).

 

Sounds like you already have an external regulator if you are charging at 14.5 + 0.7 V = 15.2 V. No standard internal regulator will charge at such a high voltage (unless being fooled by a couple of diodes in the circuit of the sense wire to make the sense voltage look lower) but most of the latest smart ones go up towards this value. This is the way to drastically shorten your charge times, but you do need to keep an eye on the battery water as they will gas a lot more at the higher voltages. This gets to the nub of your problem I think in that moving the sense wire to the house battery will allow you to get a faster and better charge, but your smaller start battery will be bubbling away at 14.5V or higher while the house battery is accepting bulk charge. It might not last too long especially if it is one of those that is supposedly "maintenance free" and requires breaking the plastic seals to get to the cells.

 

There are products out there that have the latest MOSFETs built in and outputs to two battery banks. One is the Sterling "Alternator to battery charger" from the UK. This claims to be the most advanced in the world. It even works with an internal regulator by fooling the sense and then splitting the output across the two banks. They are not cheap though - something in the range of $400 to $500. Here is a link to them - http://www.sterling-power.com/products-altbatt.htm. We use an older sterling product - the Advanced Digital Regulator which is about half the price, but this just charges one bank and it is the regulator for our house bank and second alternator. Have had it 3 years since it replaced an Ample Power advanced regulator that failed in the middle of nowhere north of Vanuatu. I had an old truck regulator on board which kept things ticking - albeit at lower charge rates.

 

So $500 would go a long way to fitting a second alternator. I'm not familiar with the Duocharge unit so can't comment on how it compares to the Sterling product. Just looking at it on the Balmar website it does not seem to have the diagnostics and setting flexibility of the Sterling unit. You can of course build the series unit yourself if you can find a good design and buy the bits, but although you might get it working, the commercial units have loads of great diagnostics - flashing LEDs, remote meters etc that you are unlikely to be able to do yourself. If you are planning long offshore trips I would bite the bullet and add the second alternator.

 

Cheers

Pete

[wheels 543]

Things we learned along the way; one b section belt won't drive a 90 amp alternator for long,

Correct. Once you go to 75A and above, you need to look at twin belts. But that is not always easy. You can look at another version of a belt though. A flat belt called a Serpentine belt. It has ribs along the length of it. NOT a toothed belt. The name comes from the fact that it can run around idlers using the back of the belt and so the path can be all over the place. These flat belts can deliver a tremendous amount of power while still using a single flat pulley and are extremely efficient.

 

Once a diode is conducting in its forward direction it is EXACTLY like a resistor.

Pohopetch, I understand exactly what you are saying, I am just trying to keep it real simple. The Diode goes in the sense line. NOT the main current supply line. So it does not see the full Current output of the Alternator's charge circuit. Hence why using the Diode instead of a Resistor. Plus that forward conduction loss of 0.7V (for a normal Silicon diode) remains constant no matter what the voltage and current in the sense line does, where as a Resistor is not going to remain such.

 

EE, Firstly, are you sure there is not already a Diode in the Panel? Most do these days. You certainly don't want two in the circuit as you are wasting energy across the diode.

A Solar regulator is absolutely the best way to go. Several reasons why. The first is that it has that same ability as a Diode to stop voltage going back the otherway at night. Depending on the quality, this can be done from simply a diode, to more sophisticated means with no loss.

Then you have three different means of regulation. El Cheapo is a simple regulator that looses the excess energy as heat. You don't want that. Second is a PWM (pulse width modulation) that regulates the energy in a far more efficient way, but heat is still wasted to a point. These are still a good Regulator and will work fine. But if you don;t mind spending the bucks and want the most of everything your panels can produce, you need to look at an MPPT (Multi Point Power Tracking). This one works well because Solar panels don't. They do not produce Voltage and Current uniformaly. Current peaks at a different point to the Voltage peak. So this cleaver little device "tracks" those points and alters how it gains the power from the panel. The output remains relatively constant, while the input changes. The other tricky thing it does is that the Resistance of a Solar panel changes also as the voltage goes up and down. The regulator alters the way it presents itself as a load to the panel. So it can still gain a good amount of power even when the Sun is dropping or a shadow is cast on the panel that the panel output is dropping away.

 

Ferrari, the VSR's (voltage sensitive relay) use depends on the trip points. So for instance, the 13.7V on 12.8V off unit that EE has shown would work like this. The alternator starts producing 13.8V when it is putting out full power. The VSR cuts in and both banks charge. The Engine shuts off and the battery being used as the "reference" battery will start to drop.Once it reaches 12.7V, the switch cuts out seperating the two banks again. Now in theory, that will work. But in reality, the different banks will not accpet the same charge and you can risk having a bank either overcharged or undercharged and certainly different to each.

 

And yeah, some Maintenance free batteries are called that, simply because you can do no maintenance, even though it probably needs it. It is a simple FLA that you can never top up. Only Gell and Glass mat is maintenance free. And although most of us probably won't come across them, so are the new Litium Ion.but that is a whole new story with a whole new way of charging.

 

And finally, there is an inherant fault in many of those alternator multi step regulators that you all need to be very aware of. I don't know about the Stirling product, but many, including a very well known and expensive unit, have no overvoltage protection. And if they fail in that area, and they do, they can cause a lot of damage to your electronics. One that failed here took out 11K worth of onboard electronics.

[wheels 543]

Apart from twin Alts, I don't believe there is a better way to split a charge than these.

 

http://www.studer-inno.com/?cat=mosfet_ ... _splitters (the unit I have )

 

http://www.thetoolboxshop.com/0-852-06- ... 3500-p.asp

 

http://www.alphatrononline.com/Battery_Isolators.cfm

[Farrari 4]

The Diode goes in the sense line. NOT the main current supply line.

 

Ummm .... my diodes are in the main power feed between the alternator and the batteries. I understand that some have a diode on the alternator sense as well to counter the 0.7V drop but not in my case as my smart charger takes care of this.

 

Wheels, I do hear you on the KISS approach though. It's worth some further thought. I only have a 27HP VolvoPenta and it already gets loaded when I charge the batteries and flick in the freezer clutch at the same time. I'm not sure how it would cope with dual alternators + freezer. Food for thought.

[wheels 543]

Right, so I better be clearer here then.The diode I am talking of directly above is purely the one that goes in the snes line and causes the Alt to raise it's Voltage by that amount.

The main splitter Diodes do indeed go in the main Charge line.

 

Alternators have different cut in RPM's. So you can change the cut in point by altering the pulley size. Or if you look at it another way, you can alter the pulley so as the engine needs to rev a little higher to get the Alt to Charge. Thus the Hp is higher. Diesels Hp is based on RPM. Certainly having a major load on the engine at idle is not good for engine for long periods is not the best for the engine.

[Guest]

Cheers Wheels.

 

MPPT (Multi Point Power Tracking) is $350 plus gst - ouch.

 

http://www.cteknz.co.nz/tabid/319/CategoryID/572/ProductID/1980/Default.aspx

 

Given power usage hasn't been a problem (LED's, no fridge, one of the 5 day ice boxes instead and pull start on the o/b) I think I'll give it a miss and do my usual 'switch the panel on in daylight' gig for now. Good solution though - nice little unit and claimed 30% higher output.

 

I havent run out of juice (yet) - the autopilot is the heavy drainer but the panel would never keep up anyway so I keep auto pilot for only when I need to go forward or get a beer which doesn't take long. Everything else is now within reach thanks to lots of colored string

 

Thanks

 

EE

[Guest]

Anyone want a brand new VSR?

 

Circa $102 retail.

 

$40 will do it.

 

PM me

 

EE