Charging/split charge relay problem

davef said:
Thanks for replies - looks like I should replace the VSR with a dc to dc charger. There was no habitation battery or charging when I got the camper, so I fitted the wiring and VSR using cabling to take 60A mistakenly thinking this would be the max that would flow from the alternator without considering the starter batteries could send large additional current. The 2.5di were fitted with 70A alternators, and there is little enough power from the engine without the extra load of a more powerful alternator! The Renogy unit looks interesting in that with 2 switches on the dash I could turn it on or off and at full power charge or at half charge., so will probably go with that. As Trev suggests maybe waiting for the starter batteries to charge back before turning it on.
The current set-up has been running for 8 years and this is the second time it has blown the fuses in that time - originally I fitted 2 x 25A fuses - but probably the habitation battery has rarely got very discharged, having a solar panel topping it up, and only powering led lights, water pump, and Propex heater. But of course the solar panel is of little benefit at this time of year.
Click to expand...
My setup costs about £10/15 bucks and works 100%, yes buy expensive b2b unit if you like, me i like to keep my pennies in the pocket.
Good luck with the job.
 
trevskoda said:
My setup costs about £10/15 bucks and works 100%, yes buy expensive b2b unit if you like, me i like to keep my pennies in the pocket.
Good luck with the job.
Click to expand...
I agree Trev, your system gives excellent bang for the buck.
Here's a question to ponder ; With all the fancy tech we have on our vans these days do you think we'll eventually be able to monitor the charge/discharge current from the alternator? I was thinking something like this could be really useful but I guess we'll have to wait for technology to improve before we'll be able to get such a device eh.
 

Attachments

  • amp meter.jpg
    amp meter.jpg
    72.1 KB · Views: 16
Pudsey Bear said:
Should be easy enough to implement Merl, old cars and bike used to have an ammeter

Click to expand...
I can imagine the conversation at the fiat dealership.
"Boss, a customer wants me to fit vis ere Lucas Ammeter, but vere's no instructions of how to connect it to the ECU and how to it interfaces wiv the CanBus."
 
You'd know better than myself Merlin but would it need to involve any of that at all?

It's just wired in series with the output I thought.

And I assume the ECU would be monitoring that anyway so it might be possible to just have that feed into a dash gauge somehow.
 
Pudsey Bear said:
You'd know better than myself Merlin but would it need to involve any of that at all?

It's just wired in series with the output I thought.

And I assume the ECU would be monitoring that anyway so it might be possible to just have that feed into a dash gauge somehow.
Click to expand...
No ECU or canbus Kev, I was simply being a sarky twat.🙄
Ages since I had awt to do with one (mid 70s on my first Austin mini) dead simple, it just went in the charge lead from alternator to battery AFAICR, with the fusebox connected to the alternator side so it then showed the difference between current generated and current consumed. Without the engine running but with lights/ wipers on it this showed the discharge current.
 
merl said:
I agree Trev, your system gives excellent bang for the buck.
Here's a question to ponder ; With all the fancy tech we have on our vans these days do you think we'll eventually be able to monitor the charge/discharge current from the alternator? I was thinking something like this could be really useful but I guess we'll have to wait for technology to improve before we'll be able to get such a device eh.
Click to expand...
Yes you can via a shunt on the negative of the chassis battery, a shunt would have to beefy enough to cope with starter current. a shunt would also be required on the negative of the aux batteries and the currents aggregate.

Alternatively an easier option would be a current clamp on the cable between alternator and battery.

loads to read here
gmw.com

Current Clamps: What they are, the different types, and their applications

In this article, you’ll learn the ins and outs of current clamp technology, and the best types of current clamps to use in challenging environments.
gmw.com gmw.com
 
merl said:
Not sure how the van batteries could contribute to charge current into the hab battery TBF?
I'm thinking it probably wouldn't be possible to blow a 60A fuse with a 70A supply, fuses need their rate exceeding before that fatigue eventually and some of the current would inevitably have to go to the van batteries too.
As I said previously, I think it's more likely the fuses were taken out by a heavy REVERSE current coming FROM the hab battery to the starter motor, this would happen if the VSR operated incorrectly.
Just a theory mind :unsure:
Click to expand...
An alternator is connected to the chassis battery positive the relay is connected to the chassis battery positive.
when the relay is engaged the chassis battery and alternator are both connected in parallel with the aux battery.

The current flow to the aux battery is also from both sources hence dead easy to blow underrated fuses or in extreme cases melt inadequate relays or wiring hence why the fuse should alway be the weakest link.

if the aux battery is heavily discharged then a lot of current will flow from the chassis battery to supplement the alternator for a relatively short period of time (or until any underrated part of the circuit fails) then the current will gradually tail off as the two voltages equalise.

hth.
 
Thistle said:
An alternator is connected to the chassis battery positive the relay is connected to the chassis battery positive.
when the relay is engaged the chassis battery and alternator are both connected in parallel with the aux battery.

The current flow to the aux battery is also from both sources hence dead easy to blow underrated fuses or in extreme cases melt inadequate relays or wiring hence why the fuse should alway be the weakest link.

if the aux battery is heavily discharged then a lot of current will flow from the chassis battery to supplement the alternator for a relatively short period of time (or until any underrated part of the circuit fails) then the current will gradually tail off as the two voltages equalise.

hth.
Click to expand...
Hence i used h duty battery cables and big trip fuses at both ends, mind you i dont run my les batts down much so no real problem, but my sys works without being over complicated and expensive, not that im tight or anything, squeek.
One thing for sure is when all linked and running engine i have jump started a few folks with flat batteries in big 4/4 jeeps.
 
Thistle said:
if the aux battery is heavily discharged then a lot of current will flow from the chassis battery to supplement the alternator
Click to expand...
Current flow is driven by PD (potential difference) ie no PD = no current.
The alternator potential will always be higher than the cab batteries potential therefore current will always flow from the alternator INTO the cab batteries
Current Can't travel in 2 different directions along the same conductor so no current can flow from the cab battery while the alternator is running therefore the cab battery can never supplement the alternator with current to the hab battery.
Current flowing to the hab battery therefore must be no higher than the output current of the alternator (70A) minus whatever is flowing into the cab batteries.
A little counter.imtuative for sure but you canny defy the laws of physics captain.😊
 
Thistle said:
Yes you can via a shunt on the negative of the chassis battery, a shunt would have to beefy enough to cope with starter current. a shunt would also be required on the negative of the aux batteries and the currents aggregate.

Alternatively an easier option would be a current clamp on the cable between alternator and battery.

loads to read here
gmw.com

Current Clamps: What they are, the different types, and their applications

In this article, you’ll learn the ins and outs of current clamp technology, and the best types of current clamps to use in challenging environments.
gmw.com gmw.com
Click to expand...
Well my attempts at sarcastic humour didn't work with Kev or Thistle! 🤭
C'mon.you pair, I actually posted a picture of an old Lucas ammeter 🤗
 
trevskoda said:
Modern day one for the van, i have the volt meters, one for starter and other for hab batts.View attachment 125840View attachment 125839
Click to expand...
Here is a second unit that could be used to replace the dash switch Trev. It measures current (which you'd fit in the main alternator lead) and then can be set up to switch your split charge relay on/off accordingly.
Slight problem is it's current limit of just 10A so it would need a second thinner cable running alongside the main alternator cable supplying just this unit.
www.ebay.co.uk

DC12V 0-10A DC Current Detection Module Current Sensing Detect Relay Control New | eBay

Detection range: DC current between 0~10A. Detection accuracy: 0.01A (10ma). Current detection module 1". Simple operation and wide application range. Standby current: about 20ma. Good performance and long service life.
www.ebay.co.uk

I know my original and patented bonnet mounted 'Paddy Hopkirk' long toggle switch with a beer mat Gaffa taped to it' device was a bit crude, this would be somewhat better.
 
merl said:
Here is a second unit that could be used to replace the dash switch Trev. It measures current (which you'd fit in the main alternator lead) and then can be set up to switch your split charge relay on/off accordingly.
Slight problem is it's current limit of just 10A so it would need a second thinner cable running alongside the main alternator cable supplying just this unit.
www.ebay.co.uk

DC12V 0-10A DC Current Detection Module Current Sensing Detect Relay Control New | eBay

Detection range: DC current between 0~10A. Detection accuracy: 0.01A (10ma). Current detection module 1". Simple operation and wide application range. Standby current: about 20ma. Good performance and long service life.
www.ebay.co.uk

I know my original and patented bonnet mounted 'Paddy Hopkirk' long toggle switch with a beer mat Gaffa taped to it' device was a bit crude, this would be somewhat better.
Click to expand...
Yes will work, but to much load just after startup, and no way of linking all batts up for a helping jump start, better to let the alt bring the starter batt up first after cranking as this is by all accounts the important one, then say after a few miles kick in the les batts, mind you i have forgot the odd time for a few miles before my brain switches on. 😂
Hence the 2 volt meters on dash, left one less batts right starter which by purpus was put next to the s wheel.
 
trevskoda said:
Yes will work, but to much load just after startup, and no way of linking all batts up for a helping jump start, better to let the alt bring the starter batt up first after cranking as this is by all accounts the important one, then say after a few miles kick in the les batts, mind you i have forgot the odd time for a few miles before my brain switches on. 😂
Hence the 2 volt meters on dash, left one less batts right starter which by purpus was put next to the s wheel.
Click to expand...
I was thinking you'd simply leave your system exactly as it already is. You'd use the relay contacts on the Ebay unit to work in parallel with your dash switch.
The Ebay unit would monitor the charge current to the van battery and then when the current dropped to a specific level (which you can adjust) then the ebay unit relay would click in and bring in your HD relay to charge your les batt automatically. Because you'd leave the dash switch in place you can still get your emergency boost.
 
You must log in or register to reply here.

Users who viewed this discussion (Total:0)

Back
Top