Camping Interior Heavy duty charging

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Posted: Thu Sep 14, 2006 2:14 pm    Post subject: Re: Can use the split charge to charge all 3 of my leisure b's? 
(Also discusses improvemements to charging efficiency, Leisure Vs Starter batteries, and charging spike reduction)

Ringo: I've currently installed a split charger circuit to charge one of my leisure batteries - but i want to extend it to charge the other two up also.

I know how to do the electrics, but am unsure what rating my alternator is and will I break it.

DiscoDave: As long as the batteries are not totally flat your alternator should be up to it! If you want to upgrade your alt got to the scrappers and get one from a 3 series BMW- 80s type and it should be a straight swap!!

Irish.David: To be honest the weak link in the chain is unlikey to be the alternator. Most of the alternators in these vans have a maximum 90A output. Although this is only at 12v you still need some pretty thick cabling and heavy duty relays to switch this. Most of the time you'll never get anywhere near the 90A from the alternator to the leisure batteries but if you start the engine after days of discharging a number of leisure batteries on the same circuit then you can get some pretty high currents.

After investigating this one my westy i found a number of components that had been fitted that could conceivably run worryingly close to their maximum limits. I can't remember the exact value but the relay fitted in the split charge circuit had a maximum rating of something like 16A. This means that if the combination of charging the battery and running any load (like eber's or stereos) went above about 200W and the relay was running outside it's safe limits. It's worth mentioning at this point that the fridge is on a seperate circuit.

The cabling used was a bit of a joke as well. In my opinion the original wiring in the charging circuit is routed wrongly (although some may disagree). It runs from the alternator to the junction box in the front left of the engine bay and then, through a split connection, on to the main coil connection of the starter and back to the battery through the charging circuit. For a low voltage circuit this is an amazing long and torturous route with plenty of unecessary resistance and, hence, voltage drop. All the cabling for the split charge circuit was under rated and the earth strap for the leisure battery was pretty pathetic.

The affect that age has on all these lengths of cabling is that the resistance goes up and suddenly an increased portion of the alternators output is used heating all the wiring and not charging the batteries. Batteries don't last as long as they never get a full charge as the voltage from the alternator is reduced before it arrives. Starting is also more sluggish as the main starter cables resistance means yet more lost energy.

None of this presents any huge danger as it's highly unlikely any of these problems would cause a wire to burn through it's insulation but i'm always extra careful in dealing with unfused wiring.

My solution was to totally rewire the 12v charging/starting cabling in the van. The only place i could find the stuff i needed was

I replaced the starter cable with the 475/0.4 starter cable. Overkill as it will carry 415A but it's almost a 2m run from the battery to the starter so I wanted some more that capable of turning the starter without wasting it all by heating up (van now starts in all conditions with under 2 turns of the crank).

I ran a direct connection from the alternator to the starter terminal of 126/0.4 which, again is overkill, but i'd rather overspec than underspec. I ran a spur of 44/0.3 to the junction box in the engine bay from the starter terminal to supply the engine which can deal with much more current than the engine will need. I then rewired the whole split charge system using 126/0.4 and a relay capable of switching 70A. The voltage between the alternator and battery is now down to 0.04v

Finally i replaced the earth straps on both batteries with 16x32/0.3 and added an extra strap on the engine. I've seen quite a few examples of upgraded wiring where the earth strap is original which renders much of the wiring pointless.

I apologise for the size of this post but there is quite a bit on here about sluggish starting vans and dodgy electrics. Might be worth adding the main starter cable as a possible culprit.

(Phew, I need a sit down after that!)

Ringo: Thats awesome - thanks very much.

I have fitted the split charge myself so im confident that its spot on. Im not sure what thickness the cable is but will have a look in the shed tomorrow. Im pretty sure its way over spec'd - something like 90A rating. However, i will double check as i built the circuit for no more than 30A.

I got an automotive relay from the noddy shop and its only rated 30A. Also, i have inline fuses of 30A.

Im quite happy with the fuse rating (if it blows i'll investigate) but i will have to change the relay.

My engine battery is in the engine bay - so thats cool. Im going to change the main battery lead when i get one made up.

So what i have to really think about is handling in excess of 30A if the leisure batteries are flat.

First things first - check the rating of the cable i fitted and double check the earth connections. I will see what to do then.

Thanks for your time Dave - I was thinking on completely the wrong wavelength here but you've put me straight.

Jolly Boy A: Could you install a switch to select which LB is charging? A bit of a faff having to change over but at least it means you won't be overloading the alternator.

Ringo: Not a bad idea that. I had considered it honest!

What i do now is charge the two batteries that arent connected to the split charge system with a battery charger. After i have done this i could switch them "in" to the split charge circuit. If i think i have flattened the batteries (i.e parked up for a week) then i could switch them "out" until i have charged them from the mains.

First though, im going to investigate if i can wire them in permanently.

Irish.david: As long as the batteries are wired in correctly there's not really any need to charge them seperately. As long as they're connected correctly it's not really possible to "overload" the alternator in the way i think you mean. The alternator will supply a maximum of 90A in any given situation. Doesn't matter how many batteries you connect (within reason), it's not going to give any more. That's assuming of course that the batteries are serviceable and aren't shorted across all the cells (v.unlikely).

If you think of the batteries as containers you can either fill one of them up at a time or wire them in parallel and fill them all at the same rate. Either way the total volume in the containers is the same.

Once again it comes down how much the wiring can cope with. As longs as there is wiring from the alternator to the Lb's that can cope with 90A maximum then I think you're better off keeping them wired together.

lhd: This is very interesting. I too would like more than one leisure battery, but I know nowt about electrics. I was going to go down the generator route, but would much prefer to add an extra battery. My van is a Westy 1.6d n/a and the main starter battery is in the engine compartment, unlike my brothers Autohomes Karisma ( petrol) which is located under the seat where my leisure battery is. Due to location, I am limited in the size and power of the leisure battery and was wondering if I could change this. It is such a pain having to drive around just to charge the leisure battery, and as previously stated the Eber does seem to suck the life out of it. Is anybody capable of drawing a diagram including wire & relay ratings that an idiot could follow................. What I was thnking of was relocating the main battery under the seat and putting two large leisure batteries in the engine compartment, as this is the only real available space to locate them without losing storage space.... Also as the weight of the driver,and units are all on the n/s This would be ideal in trying to equalize the weight distribution. many thanks ....

Irish.david: Fitting a second leisure battery is quite easy in theory. All you need to do is connect the second leisure battery in parallel (positive to positive and negative to chassis) with the existing leisure battery. The thing to remember is that when you do this the current required to get both batteries from discharged to fully charged is doubled. So i'm afraid that we're now back to making sure your cabling and switch charge relays can cope with the extra current.

As far lhd's query about moving batteries from location to location, it's just a matter of re-routing and replacing the cables. Trouble you're going to have is that moving the main battery further away from the starter is going to cost you. If you check the prices on the website i mentioned earlier, high current starter cable is expensive. You could go with cheaper stuff but as a rule of thumb, the longer the run of cable the higher current it needs to carry and the thicker and more expensive it is. The other problem is that it's not practical fitting a fuse on a cable of that current rating. This means that you have to be very careful routing it as if it rubs away the isulation and shorts on the chassis you are going to be in for the mother of all firework displays.

If i was you i'd keep the starter battery where it is and add some batteries under the empty front seat or under the rock and roll bed. Then add a split charge relay in the engine bay and run a single length of 126/0.4 from the relay and parallel up the leisure batteries.

On the subject of batteries, i'd like to add that for 95% of van users leisure batteries, or deep cycle batteries are a waste of money. These batteries are intended for use in equipment that is run once and then not used again in months, like caravans, boats, golf carts etc. They have thicker electrode plates that regular batteries and have a lower power density. As long as you run your van once a fornight then an ordinary car battery (63Ahrs fits well under the seats) will give you better performace for much less money.

As far as eber's flattening batteries goes thats a sure sign that something is wrong. I've only had experience with the B2L/D2L thats fitted in westys but once they're up and running they should only draw 15W. This means that on a fully charged 63Ahrs battery they should be able to run for about 50 hours (i know i'm over simplifying the maths but its a rough estimate). This suggests two things might be wrong.

The first is that the B2L/D2L is fitted with a temperature switch that means when the eber is up to temperature it shuts down the glow plug and saves lots of power (150W to 15W). The spark/heat in the eber is enough to continue combustion. If your temperature switch is faulty then the glow plug stays on and it keeps drawing 150W. These switches can fail as they get older and cause this fault.

The other, and more likely problem, is that the leisure battery is never getting fully charged due to losses in the wiring. The way to test this is to measure the voltage at the alternator with the engine running and compare it to the voltage at the main and leisure battery. The difference is due to the loss in the cabling. It's been mentioned previously that a drop of 0.5v is acceptable but this still means that if the alternator is supplying 90A (unlikey but possible) the cabling is "eating" 45W of power. Also if a 12v battery is only getting a charge from a 13v supply it'll probably never charge to full capacity.

After rewiring the whole starter/charging system in my van i've got the voltage drop from 14v down to 0.04v for the main battery and 0.07v for the "leisure" battery. I'm hoping that with one more "tweak" I can reduce this further.

Its more hassle but if you've got a significant voltage drop at your leisure battery, before adding more batteries, i'd recommend re-doing at least some of the wiring.


PS : If you upgrade the split charge relay make sure there is a diode in series with the relay coil, either in the relay or fitted yourself. When a coil is de-energised it can spike up to a few thousand volts which, if not diode protected, could fry the alternator. Sorry for another endless post.......

(I think he needs to sit down again after that...)

dbroada: I have to admit to not taking in all of irish.david's post but do have a couple of comments to make.

I don't entirely agree about deep cycles being a waste as they do stand repeated discharge more readilly than a starter battery. My one year old starter became dead after 5 total discharges, Fortunately the factors I bought it from replaced it free as it was less than 18 months old and I have now tracked down most of the causes of the current drain. Admittedly a deep cycle will also suffer if repeatedly discharged. Of course it is better to not totally discharge so either type will do.

Next, using an alternator is not going to fully charge a battery. As the voltages converge the current getting into the battery gets less. As a "rule of thumb" you will only get about half the AmpHour capacity out of a battery. If you really need more capacity (and have deeper pockets than me) you should be looking at intelligent chargers instead of a alternator based option.

Oh dear, I've just re-read that and it looks like I'm trying to appear clever. irish.david clearly knows his stuff (more than I do) but I'm just trying to show a few options.

if you do deeply discharge your batteries you would be better off using a diode separation unit rather than a split charge so that the main battery doesn't try to charge the flat batteries with a big current surge. _________________

dbroada: How long would a normal car battery last if the van is used on a regular basis?

I was going to say that this is a "how long is a piece of string?" question - but it isn't really. If you have a piece of string and cut off an inch a day you will eventually see that it's going to run out. Our little chemical reaction in a box will, under the right conditions, fully restore.

Another problem is being able to determine the state of our battery. A volt meter and/or a hydrometer can tell if the battery is empty or full but neither can tell "how full". Also, 2 devices of the same wattage can discharge a battery in different ways. In other words, no real way of telling.

From what I have read it is leaving the battery in a discharged state that is the problem. There are enough people around who have used starter batteries as leisure batteries with no problems to conclude that under "normal" use you should be able to get through the full warantee period. (Halfords do 7 year warantee batteries don't they?)

The worst case is if when camping you discharge your battery deeply. When you start the engine and the relay kicks in there is a chance that a fuse will blow. (Caused by the good battery trying to charge the flat one). Now you drive home and park for a week without realising that you have a flat battery. You can only do this a couple of times to render either type of battery useless.

I have googled for "lead acid battery charging" and come up with many (often contradictory) articles. This one - [1] - makes some sense to me.

TonyTech: Warning Re: using a diode as spike protection

Ideally the diode should be reverse biased across the relay. i.e. connected across the coil in a direction that does not conduct when the relay is activated. (White line on diode to +ve)

Putting a diode in series will drop 0.7V and my result in the relay not activating.

Irish.David: Final comments

Sorry i left the discussion for so long but i was doing a bit of holidaying over the weekend.

Apologies for the diode setup mistake. As Tonytech said it needs to be reversed biased in parallel with the coil.

As far as the leisure battery situation goes, with my usage pattern a normal car battery is a better bet. I tend to run the van at least once a week for long enough to fully charge both batteries. If i'm ever parked up for long enough to really discharge the 2nd battery (so the interior lights are dimming) i'll try and run the engine for about 15-30 mins to give the 2nd battery a hand until i next need to do a bit of driving.

The problems using car batteries as a 2nd battery will only really appear if the battery is sitting in a discharged state for a period of time. Once the charge nearly runs out on a normal battery the internal plates start corroding due to galvanic action and damage occurs. This process isn't particulary quick so as long as you put a bit of charge on the battery before too long then the damage is minimal. If you forget to turn the sidelights off at night and wake up to a flat battery you can jump the van and re-charge the battery without any real damage to the battery. If the van will be sitting unused for a long period then fully charge the batteries and disconnect the earth straps.

If your batteries are discharging themselves when you're not using the van then you've got a problem somewhere. You can check this pretty easily.

First, with the engine and all equipment in the van switched off, disconnect the earth strap of the battery you want to test. At this point, i like to tap the connector of the earth strap against the -ve terminal of the battery just to ensure there's not a major problem. If you do this and get big sparks, then you've either left something on or there's a big problem somewhere. If you connect a meter to a setup in this state there's a good chance you'll kill the meter. A few little pin pricks of light are ok.

Next set your multimeter up to read current. On most meters this involves plugging the test leads into different sockets than you would to read voltage. Start with the highest current rating on your meter and touch one lead to the connector on the earth strap and the other lead to the -ve terminal on the battery. The reading on the meter should be below 0.1A. If it is then set the meter up to read the lower of the current readings and connect the terminals to the same place. Depending on what equipment (alarm, immobiliser, central locking, etc) got installed on the van will determine how much current is leaving the battery, but on my van i'd be worried if was over 10mA and ideally it should be well under 5mA. Higher values means that even with the key out and the doors locked your battery is discharging.

Something else was mentioned in an earlier post that illustrated a problem that quite a few people are having that could appear to indicate a faulty battery but could actually be something else.

Quote: using an alternator is not going to fully charge a battery. As the voltages converge the current getting into the battery gets less. As a "rule of thumb" you will only get about half the AmpHour capacity out of a battery

While it's true that when the voltages converge the current going into the battery gets less, i don't entirely agree that you only get 1/2 the Amphour capacity from a battery charged by an alternator. Intelligent chargers merely regulate the voltage so the most efficient current flow is delivered to the battery at any given point. Lead acid batteries are amazing flexible and can accept a vast range of charging currents with neglible loss in capacity. Intelligent chargers are more suited to the more "prima donna" type of batteries such as Ni-MH or Li-ion which have an stupendously high capacity in a tiny space (which scares the hell out of me). Alternators are designed to output 14v (about 1v above the open circuit cell voltage of the battery) so the battery can get almost fully charged during a decent journey.

Electrical cables have resistance that's proportional to their length ie longer cables higher resistance. In an electrical circuit the higher a components resistance then the more voltage is developed across it. This is why in almost all cars the battery is close to the alternator and starter.

Imagine that a car has a 20cm run of cable between the alternator and battery. The alternator is producing 14v and the voltage at the battery is 13.9v. This means that there's a voltage drop of 0.1v in the cable.

Now imagine in a van that the cable, battery and alternator are the same but instead there's a 2m run from the alternator to the battery. This means that there will only be 13v developed at the battery as a full 1v is lost in the cabling.

If 13v is being developed at the battery and the open circuit cell voltage is about the same then the battery isn't going to get anywhere near fully charged.

As has been mentioned previously the alternator's on our vans are just plucked from cars so aren't designed to cope with this extra cabling distance. When the vans were new then this probably wasn't such a problem as the new cabling had a low enough resistance so the losses were negligible. 15 years on the resistance of the cabling has increased and the voltage at the battery has dropped.

Again this is easy to check. Start the engine then set your multimeter to voltage measurements (make sure you do this or the meter is going to come to a violent end in the next step) and measure the voltage being developed at the alternator terminal. Just touch the red wire to the main alternator terminal and the black to the metal on the alternator body. Make a note of that and then measure the voltage being developed across the batteries on the battery terminals themselves. Any difference between the alternator voltage and the battery voltage is the cable losses.

An acceptable loss of 0.5v has been mentioned in previous threads. To be honest 0.5v would get the battery nearly fully charged on a long run but i'm slightly obsessive over cable losses so i re-wired my van. If you own a petrol van then you can probably make a big improvement on the voltage drop just by running a direct cable from the alternator terminal to the main terminal on the starter motor. If you want to do this make sure you disconnect and secure the earth straps on both batteries before re-wiring.

You don't need special cable. If you can get hold of some 13amp mains cable and splice the live, neutral and earth together you'll get a fairly high current cable and should notice a big difference at the battery.

On the subject of draining the main battery by starting the engine with a deeply discharged 2nd battery and a split charge circuit i'm afraid that it again comes down to the cabling. If you're getting nearly the full alternator voltage at both the main and 2nd battery with the engine running then you'll never drain the main battery. The alternator will hold the voltage at a level so the 2nd battery gets all it's charge from the alternator and the main battery will charge at a slightly slower rate. Personally i don't have my split charge circuit fused (to be honest if you know the cabling's ok then i don't see the point). I'd strongly recommend against a diode seperation charging system for the 2nd battery. The voltage drop across a forward biased diode is going to severly limit the voltage that can be developed across the 2nd battery.

Another point mentioned was starting currents. Even if you take into account the mechanical losses i don't think that you'd get anymore that 200-300A continous current for the starting motor if the engine is healthy (800A could occur as a peak when the solenoid engages). My reason for overspecing is that at a small premium to myself i can drastically reduce the stress on my starting system by ensuring that it gets almost all the power to start the engine when i turn the key. And it'll last longer than the van. It's worth noting that it looks like VW used the same starting cable for the 2m run that it would use on a 30cm run in a car.

Although i have no hard evidence for this i can guess about the setup of the electronics in DJ engines using 80's electronics as a guide. The current draw for the electronics on DJ's should be almost neglible (no more than an amp plus the fuel pump). They should also be resistant to voltage drop. The control circuits in the ECU will almost certainly run on 5v switching 12v outputs. Both these voltages will be regulated so as long as the cabling isn't broken the engine will run. As the supply also feeds the HV side for the spark plugs it's almost certainly filtered for spikes as well. I could be wrong about this so this is not to be taken as fact.

Once again, i apologise for such a long unwieldy post. I'm leaving the country again tomorrow so maybe this thread will be able to die.


PS : Popeye - The eber's have an undervoltage protection in them. Assuming the fans blowing, try the fuel pump and failing that the glow plug.

HarryMann: Vehicle Wiring Products lists: Relays with diode. These relays have a diode in the coil circuit to protect against voltage spikes in sensitive circuits. Supplied with loose bracket