Battery problem

[Deleted member 12051]

This device is just a pair of diodes on a box. Pretty good diodes that can carry 10 amps (or more with a heatsink added), but diodes none the less. I forget how much voltage they drop. I may remember to measure it later.
It's clever in that it won't let electricity flow from one battery to the other, but if you put a voltage on the input, the battery with the lowest voltage will get the charge.
Unfortunately, that may not be what you want. If one battery is fully charged, it's voltage will be perhaps 13v. The other battery is only half charged and the charger would be bringing it up to 14.5v in the bulk charge phase.
This device will push power into the wrong battery in this situation.
But a bigger problem is that if you connect an mppt solar controller to its input, the controller won't work: they require a power feed from the battery to start up, and this device stops them getting any power at all.
This device has its uses, but if you are keeping the batteries maintained in a long period of layup, a wire with a fuse or a 21w bulb in line is a better approach.

Last paragraph h on how this could be done?

 

[harrow]

0.7 volts

 

[in h]

Last paragraph h on how this could be done?

It's really easy. Use a wire that will reach from one circuit to the other. Doesn't have to be to the battery terminals: the current will be very small, so any circuit that is powered by the engine battery will do, and any circuit that is powered by the leisure batteries.
At some point in the wire (where it will be convenient for you) fit an indicator bulb. A proper bulb, not an LED! You could solder the wires to the bulb, but probably most people would prefer to use a bulb holder.
One connection to each battery's positive side, neither to earth.
An indicator bulb is normally 21 watts, so it will be designed to run at about 1.5A in normal use. That means it will have an impedance of around 8 ohms when running, perhaps 6 ohms when cold.
Assume that one battery is at 12.0v and the other is about 14.5v (on boost charge) so the voltage difference will be 2.5v. That means the bulb will pass a trickle charge of about 0.5A. Very low, but enough to keep an idle battery safely maintained.
Of course, a 55w spotlamp bulb would give a higher current (about 1A or slightly more), but few people have them in their spare bulbs set.

 

[Deleted member 12051]

So are you saying. The engine battery has a trickle charge from the two solar panels on the roof. Is this what you are describing or is this another add on?

 

[in h]

So are you saying. The engine battery has a trickle charge from the two solar panels on the roof. Is this what you are describing or is this another add on?

Not as specific as that. It will very slowly trickle charge whichever battery is lower than the other, no matter what is charging either of them.
It's akin to joining the batteries together, but only with a very slow wire.

 

[Markd]

We are a long way in and have lost track of what starter battery charging arrangements are.
My personal preference is for direct solar top up using a regulator with two outputs rather than some fancy arrangement that runs the risk of preferentially robbing charge from the leisure batteries.
On brand that has a good reputation is Votronic and a 250w MPPT regulator is c£100.
MPPT regulators deliver 20-30% more charge to batteries than PWM types so can easily 'pay for themselves'
If you don't have MPPT regulator and want to add starter charging getting a Votronic is a good value way of killing two birds with one stone.

 

[trevskoda]

Im getting a bit mixed up sorry,are you wanting to charge from solar both les and eng battery or from a onboard mains charger,my van does both ,if you tell me what you want i can draw up a w dia to work,i do need to know what bits you have so far.

 

[Deleted member 12051]

Im getting a bit mixed up sorry,are you wanting to charge from solar both les and eng battery or from a onboard mains charger,my van does both ,if you tell me what you want i can draw up a w dia to work,i do need to know what bits you have so far.

as far as I’m aware:-
I have a wired system to the starting battery, with an in-line fuse incorporated. When the fuse is inserted in the engine compartment the solar panels will charge both leisure and engine batteries. I have to remove the fuse on start up or else it blows if I don’t follow this procedure. This was on instruction from previous owner. My leisure’s are in full working order. Therefore my engine battery was to diagnose if it was goosed or just flat because of long standing over the winter.
I’m at present charging the engine battery to full capacity and then monitoring on any loss of voltage over the next coming days. My onboard system allows me to charge engine with EHU. I’m still awaiting delivery of 25amp fuses and don’t even know if they will correct my system monitor from showing 0 on the screen.This is all I can say about the engine that I know of.
Trev, I am looking for something that will keep my engine battery topped up as an alternative over the static months and your offer of diagrams etc would really be an asset to have without worry of no start up or drainage. My leisure’s are situated (very tightly) on the external part of the van and all electrics under the seat internally obviously. Your onboard mains charger sounds easier than all other technical advise which I know would require an electrician to do. I have challenged a lot of things with this van being a woman but I’m sure in layman’s terms I could follow what you’re describing. Heres hoping I've detailed to you, only what I know to date
.

 

[in h]

We are a long way in and have lost track of what starter battery charging arrangements are.
My personal preference is for direct solar top up using a regulator with two outputs rather than some fancy arrangement that runs the risk of preferentially robbing charge from the leisure batteries.
On brand that has a good reputation is Votronic and a 250w MPPT regulator is c£100.
MPPT regulators deliver 20-30% more charge to batteries than PWM types so can easily 'pay for themselves'
If you don't have MPPT regulator and want to add starter charging getting a Votronic is a good value way of killing two birds with one stone.

MPPT gives better performance from your panels, but if you have 100W of panels, it would be cheaper to add another 100W of panels than replace the controller. That assumes there is room on the roof, of course. But it would give 100% more output for the same money.
The Votronic controller is fairly good (I have one, as a spare) but it only does multi-stage charging to one battery. The other output is a small trickle-charge to the "other" battery (you can choose which gets the main charge and which is "other").
My suggestion for a bulb in a wire connection is slightly less effective, but just as useful for a long-term layup. It's also about £100 cheaper and easier to fit.

 

[in h]

as far as I’m aware:-
I have a wired system to the starting battery, with an in-line fuse incorporated. When the fuse is inserted in the engine compartment the solar panels will charge both leisure and engine batteries. I have to remove the fuse on start up or else it blows if I don’t follow this procedure. This was on instruction from previous owner.

I don't really understand this. When you have the fuse inserted it lets the solar panels charge both batteries. That means that it must be connecting each battery's positive terminals together. That makes sense.
Of course it means that if you run the leisure battery flat, the engine battery will be flat too, which is far from ideal in normal use. But I can see good reasons for joining them sometimes, such as now!
What I don't understand is why that fuse would blow if you started the engine.
Normally, there would be a split charge relay cutting in when the engine started, which would effectively take all the current away from that fuse. Have you ever tried it and seen the fuse blow?
I'm also a bit surprised that you are having to wait for a replacement fuse to be delivered. Most vehicles have a few spare fuses supplied in the fuse box.
Maybe yours didn't, or someone used them without replacing them!
It really is a good idea to have a small stock of replacement fuses of various ratings. I'd not buy cheap Chinese ones from ebay, though: they tend to be made of extra-thin metal and don't make a good contact with the fuse holder.

 

[Markd]

It does sound as if there's a direct hard link between leisure and starter batteries.
Therefore if the fuse isn't removed before starting the engine the leisure batteries join forces with the starter battery which of course slows the fuse.

All the more reason to get a dual channel such as Votronic. With 120W panel their smallest MPPT charger which is c£90 would cope.
Arguably with 3 leisure batteries more panel power would be a good idea if there is space.
A 250w Votronic is c£125 and could cope with the voltage from panels in series to avoid recabling I to the van.

Given the age of the van I doubt whether the original mains charger is actually capable of coping with 3 leisure and a starter battery which would be 400Ah capacity if they all get low.

 

[in h]

It does sound as if there's a direct hard link between leisure and starter batteries.
Therefore if the fuse isn't removed before starting the engine the leisure batteries join forces with the starter battery which of course slows the fuse.

Not in my experience, it won't.
Yes, in theory the starter current would drop the engine battery down enough to cause a hefty current through the wire, but it will probably be limited by the resistance of the wire to under what a fuse can manage.
You have to remember that the fat cable to the starter solenoid comes direct from the starter battery, and the cable to the other battery is probably long and small, though it does depend on how thin the wire is and how hefty the fuse is.
I've only done it once (by mistake) and the fuse didn't blow.

 

[trevskoda]

The voltronic is good and thats what i have,however i also have a battery to battery relay with a switch in the cab so i can connect all batterys together,handy if you find starter battery low and a boost from les batterys will get you on the move,it will also let you charge from solar to all batteries,but you must remember to switch of when camping or you will drain the starter battery,here is a dia of it,i have used the neg side to switch which means no live wires in cab,just earth the switch, proper heavy battery to battery cable should be used.

 

[Markd]

I bow to greater knowledge and experience.

 

[trevskoda]

I bow to greater knowledge and experience.

Hi loads of ways to solve a problem,my post is also handy for jump starting a second van as all batteries linked when required.

 

[wildebus]

I can do the same thing with my setup, except I can turn my relay on and off via the Internet and also set it to either stay on or set a timer for it

 

[trevskoda]

I can do the same thing with my setup, except I can turn my relay on and off via the Internet and also set it to either stay on or set a timer for it

Yes you know your stuff and i read and learn from your posts wildebus.

 

[Deleted member 12051]

The voltronic is good and thats what i have,however i also have a battery to battery relay with a switch in the cab so i can connect all batterys together,handy if you find starter battery low and a boost from les batterys will get you on the move,it will also let you charge from solar to all batteries,but you must remember to switch of when camping or you will drain the starter battery,here is a dia of it,i have used the neg side to switch which means no live wires in cab,just earth the switch, proper heavy battery to battery cable should be used.View attachment 80585View attachment 80586

Hi Trev love this idea. I don’t feel confident enough to tackle this one alone. My friend said once over this horrible period he will come and look at applying your method/diagram. Again, thank you

 

[Deleted member 12051]

I don't really understand this. When you have the fuse inserted it lets the solar panels charge both batteries. That means that it must be connecting each battery's positive terminals together. That makes sense.
Of course it means that if you run the leisure battery flat, the engine battery will be flat too, which is far from ideal in normal use. But I can see good reasons for joining them sometimes, such as now!
What I don't understand is why that fuse would blow if you started the engine.
Normally, there would be a split charge relay cutting in when the engine started, which would effectively take all the current away from that fuse. Have you ever tried it and seen the fuse blow?
I'm also a bit surprised that you are having to wait for a replacement fuse to be delivered. Most vehicles have a few spare fuses supplied in the fuse box.
Maybe yours didn't, or someone used them without replacing them!
It really is a good idea to have a small stock of replacement fuses of various ratings. I'd not buy cheap Chinese ones from ebay, though: they tend to be made of extra-thin metal and don't make a good contact with the fuse holder.

I don't really understand this. When you have the fuse inserted it lets the solar panels charge both batteries. That means that it must be connecting each battery's positive terminals together. That makes sense.
Of course it means that if you run the leisure battery flat, the engine battery will be flat too, which is far from ideal in normal use. But I can see good reasons for joining them sometimes, such as now!
What I don't understand is why that fuse would blow if you started the engine.
Normally, there would be a split charge relay cutting in when the engine started, which would effectively take all the current away from that fuse. Have you ever tried it and seen the fuse blow?
I'm also a bit surprised that you are having to wait for a replacement fuse to be delivered. Most vehicles have a few spare fuses supplied in the fuse box.
Maybe yours didn't, or someone used them without replacing them!
It really is a good idea to have a small stock of replacement fuses of various ratings. I'd not buy cheap Chinese ones from ebay, though: they tend to be made of extra-thin metal and don't make a good contact with the fuse holder.

Hi h. Yes I have experienced the fuses blown/melted on 2 occasion. I have a printed card which I have in front of my speedo to remind me about the said fuse on before start up, since my forgetting thus before Like you I don’t buy anything Chinese especially my van parts. I’m high risk and can’t get to a garage so I ordered them online and arrived yesterday. There weren’t any spare fuses at all in the box. I do have a collection of spares of my own but not 25amp - ordered 6 of these to replenish. Today, weather depending, I will insert the 2 fuses, check system monitor (holding my breath to show engine battery level). Engine battery charged and now I’m monitoring any drainage. To pick your brain again, what is the voltage after fully charged should that reading be on my multi meter? I ask, as once again I’ll repeat what I’ve discussed earlier - if it drains down and needs a new battery then so be it.
Would it drain on a daily basis? I have disconnected the solar to it as this would top it up. This has been my first encounter with batteries but I’m getting pretty knowledgeable as time goes on. Thanks to you and others being patient with me.

 

[in h]

To pick your brain again, what is the voltage after fully charged should that reading be on my multi meter? I ask, as once again I’ll repeat what I’ve discussed earlier - if it drains down and needs a new battery then so be it.
Would it drain on a daily basis? I have disconnected the solar to it as this would top it up.

The voltage you see on the battery is only an indication of its actual state of charge after it has rested for several hours, with no charge current or discharge current.

The voltage you see when it is being charged is really what the charger has decided it should be.

As the battery is charged, a good charger takes it through three or four charge stages: at first (or second for some chargers, that start very slowly), it pushes power in as fast as it can, and the voltage will go from about 12.0v slowly rising through the 13v range, then when the battery voltage reaches about 14.54v, it controls the charging at that voltage for a while. Some chargers have a fixed time for this phase, some measure the current needed to maintain the voltage at that.
Either way, when the charger is satisfied that the battery is full, it then backs off the voltage to about 13.7v. Some even have a further "back off" phase, dropping to about 12.8v after a few days

So even if all that made your eyes glaze over, the takeaway is that the battery is fully charged when its charger lets the voltage reach 13.7v, but only the SECOND time it reaches that voltage, on the way DOWN from 14.54v.

After the battery is full, if you disconnect the charger and the load, the battery should sit there at around 12.8v for several weeks or months. Unless it is faulty, or unless something is taking power from it, the battery should be 75% charged after six months doing absolutely nothing.

The starter battery normally powers the radio in the dash, the alarm (and maybe the ECU if it is a newish van), so it could possibly run down after a month or two, even if nothing is actually switched on.

In general, the old Zig chargers used to cook batteries if left on all the time, but modern hookup chargers or modern solar charge controllers shouldn't. If the battery is being left at 13.7v or maybe 13.8v when the solar has filled it up, that's fine and I'd leave the solar panel connected.

If you join the two batteries together with your magic fuse, the solar controller will look after both of them.