Charging cab / engine battery from Solar panel.

Ive often left all my vehicles for months on end with no charge. Cars get left for up to five or six months, bikes often the same and the motorhome often gets left over winter. I just disconnect the negative lead off the batteries. Seems to work.
Ask any good battery shop and you will be told not to do so.
 
Im having cab battery woes at the moment despite a new Bosch cab battery being fitted in August last year. I think my current style of motorhoming might be adding to the problem. Battery is going for testing next week as is the alternator is it was flat after two weeks sat on the front with it connected. Generally I disconnect it when parked up for some time but often when away in the van we drive from A to B and then stay in one spot for several days or sometimes several weeks. The scooter does all the miles so my concern is maybe the battery is never getting enough charge from the engine.

In the summer we have loads of solar charge though and the MPPT controller often shuts down by mid morning so what would be a simple method of putting in a splitter to top up the cab battery from time to time? Its an old van, 1996 Peugeot Boxer Kontiki 640. A job for an auto sparky I presume. I dont want to spend a fortune as I am not sure how much longer we will keep the van.
the simple way is to fit two high current diodes from the solar panel to feed charge current into both batteries.
 
the simple way is to fit two high current diodes from the solar panel to feed charge current into both batteries.
The problem with using conventional diodes is there voltage drop. Standard silicone diodes drop 0.6 volts and even Schottky diodes drop 0.3V so the batteries never receive a full charge, also if you put a diode in each leg as you suggest then the solar controller looses its power supply when over night ( no solar and no feed from the batteries) and depending on your controller it can reset itself.
For the DIY electronics enthusiast I can recommend this little device which I came up with myself.
PXL_20230329_110611317.jpg
PXL_20221112_145711206.jpg
PXL_20221112_145845363.MP.jpg

It's very simple and consists of a smart bypass diode SM7461 in series with a 12v 200W halogen lamp.
It's fitted between the 2 batteries just like any other battery maintainer but has several advantages.
1, It has NO voltage drop, the cab battery is held at exactly the same voltage as the hab battery.
2, It requires just 2 connections, no neg connection is required.
3, It's extremely efficient and consumes virtually no power in it's self.
4 It can be left connected and doesn't need to be removed when starting like the simple fuse link a la Clive circuit.
5 it's cheap, parts cost less than £15.
The 200W 12v halogen lamp is made up of 4X50W capsule lamps. The pics above are of one I built and used before I moved to a B2B. Worked perfectly.
The halogens fit nicely into a small.piece of perf board, remember to beef up the tracks with solder cos of the current. The diode doesn't need heat sinking because it dissipates virtually no power because it's either hard on ( ohh er missus) or off.
The lamps act as a very low ohm PTC thermistor, (they never light up) and protect the device/wiring in the event of cranking the engine with a flat cab battery and a full hab battery. You're probably best to add a 5A fuse in series with the device.
Merl
 
The problem with using conventional diodes is there voltage drop. Standard silicone diodes drop 0.6 volts and even Schottky diodes drop 0.3V so the batteries never receive a full charge, also if you put a diode in each leg as you suggest then the solar controller looses its power supply when over night ( no solar and no feed from the batteries) and depending on your controller it can reset itself.
For the DIY electronics enthusiast I can recommend this little device which I came up with myself.
View attachment 118821View attachment 118822View attachment 118823
It's very simple and consists of a smart bypass diode SM7461 in series with a 12v 200W halogen lamp.
It's fitted between the 2 batteries just like any other battery maintainer but has several advantages.
1, It has NO voltage drop, the cab battery is held at exactly the same voltage as the hab battery.
2, It requires just 2 connections, no neg connection is required.
3, It's extremely efficient and consumes virtually no power in it's self.
4 It can be left connected and doesn't need to be removed when starting like the simple fuse link a la Clive circuit.
5 it's cheap, parts cost less than £15.
The 200W 12v halogen lamp is made up of 4X50W capsule lamps. The pics above are of one I built and used before I moved to a B2B. Worked perfectly.
The halogens fit nicely into a small.piece of perf board, remember to beef up the tracks with solder cos of the current. The diode doesn't need heat sinking because it dissipates virtually no power because it's either hard on ( ohh er missus) or off.
The lamps act as a very low ohm PTC thermistor, (they never light up) and protect the device/wiring in the event of cranking the engine with a flat cab battery and a full hab battery. You're probably best to add a 5A fuse in series with the device.
Merl
Genius!
 
The problem with using conventional diodes is there voltage drop. Standard silicone diodes drop 0.6 volts and even Schottky diodes drop 0.3V so the batteries never receive a full charge, also if you put a diode in each leg as you suggest then the solar controller looses its power supply when over night ( no solar and no feed from the batteries) and depending on your controller it can reset itself.
For the DIY electronics enthusiast I can recommend this little device which I came up with myself.
View attachment 118821View attachment 118822View attachment 118823
It's very simple and consists of a smart bypass diode SM7461 in series with a 12v 200W halogen lamp.
It's fitted between the 2 batteries just like any other battery maintainer but has several advantages.
1, It has NO voltage drop, the cab battery is held at exactly the same voltage as the hab battery.
2, It requires just 2 connections, no neg connection is required.
3, It's extremely efficient and consumes virtually no power in it's self.
4 It can be left connected and doesn't need to be removed when starting like the simple fuse link a la Clive circuit.
5 it's cheap, parts cost less than £15.
The 200W 12v halogen lamp is made up of 4X50W capsule lamps. The pics above are of one I built and used before I moved to a B2B. Worked perfectly.
The halogens fit nicely into a small.piece of perf board, remember to beef up the tracks with solder cos of the current. The diode doesn't need heat sinking because it dissipates virtually no power because it's either hard on ( ohh er missus) or off.
The lamps act as a very low ohm PTC thermistor, (they never light up) and protect the device/wiring in the event of cranking the engine with a flat cab battery and a full hab battery. You're probably best to add a 5A fuse in series with the device.
Merl

I dunno what any of that means but do you have any plans to move to North Yorkshire? This village is lovely. :D
 
Quite possibly Trev but Ive been doing it for decades with no real problems. The problems seem to occur when you forget to disconnect them. Hab batteries seem to last about six or seven years, cars or bikes about the same generally.
Very true but better to look after them as getting expensive these days
 
There is a cheap way using diode blocks which i had before going votronic, cast about £18 if i remember, there is a slight voltage drop, made by kemo.
charge splitter.jpg
kemo 174 reg .jpg
 
Sorry there's a typo in the circuit above. The smart bypass diode is SM74611
 
That figure rings a bell, David. I found that mine never worked; in Summer, the LB was fully charged by the Solar, but we were never parked up for long enough for the VB to run down after journies of 100 miles+ to reach Rallies etc; and in Autumn/early Winter, the LB didn't get enough Solar to reach 0.5v in excess of the VB when the latter really needed it, resulting the ECU failure after 2 weeks parked in late October/early November. The new ECU was fitted around mid December and you fitted the AMT12-2 in early January 2022, since when the AMT12 has been able to keep the VB fed sufficiently, even in January and February; and by March, the extra daylight has kept the LB at around 13.5v and the VB at 12.95v to 13.1v whilst parked up [i.e. 2 x Jan/Feb periods in succession]. I did plug the VB into the mains recharge for about 2 hours in January after the M/Home had spent some 7 weeks parked during a really cold and dark spell, dropping the VB to 12.87v and the LB to 13.1v

Steve
Always found that with 2x100W solar panels for the LBs, the Battery Master kept the VB up to scratch over 4 winter months with all the usual drains, including Growler alarm.
 
Always found that with 2x100W solar panels for the LBs, the Battery Master kept the VB up to scratch over 4 winter months with all the usual drains, including Growler alarm.
Don't have the roof space for a second Solar Panel [existing Panel is 180w] and the Lithium 120Ah Battery is normally adequate for the Vehicle Battery maintenance, with the AMT12-2 set to almost constant current supply [9 seconds in every 10 seconds]. The problem was leaving the M/Home unused for 7 weeks in one hit; and the EHU 2 hours boost was very much a defensive measure having blown the ECU in November 2021, and not wanting to risk a repeat of the cost and aggro!

Steve
 
Always found that with 2x100W solar panels for the LBs, the Battery Master kept the VB up to scratch over 4 winter months with all the usual drains, including Growler alarm.
Now "Growler" around here has two slang meanings, one is a Pork Pie and the other is a part of a female, neither of which normally have an alarm on them, cept maybe at Barry's house???
 

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