Charging/split charge relay problem

[davef]

I have just replaced the alternator on my mk3 Transit. Noted it wasn't activating the split charge relay to charge the leisure battery, and found the inline fuses had blown - I put 2 of 30amp fuses in parallel. I assumed there must be a short in the wiring and checked this out, but there doesn't seem to be a wiring fault. The alternator is 70 amp, but cann't see all the power going to the leisure battery, but then it occurred to me once the voltage is high enough to trip the relay, the twin starter batteries are connected to the leisure battery which could allow a very high current if the leisure battery was low. 60 amp is probably the maximum the wiring would take, so cann't just increase the fuse size. Should I just carry spare fuses for when this happens, or is there a way of limiting the current? Or is this an inherent problem with split charge relay set-ups and why battery to battery chargers are better?

 

[trevskoda]

I wired my self build with heavy duty battery cables and a 200amp relay, this i switch on from the dash once the engine has run for a we bit.
Why have you 2 starter batts and only one les bat, should be the other way round.

 

[davef]

It came with 2 starter batteries, and does seem to need them on a cold winter morning to turn the 2.5di engine fast enough to start - obviously no glow plugs to help.

 

[mistericeman]

I wired my self build with heavy duty battery cables and a 200amp relay, this i switch on from the dash once the engine has run for a we bit.
Why have you 2 starter batts and only one les bat, should be the other way round.

Many transits do ....one main starter and one to run lighting etc ...
Both joined together for starting .

 

[trevskoda]

Many transits do ....one main starter and one to run lighting etc ...
Both joined together for starting .

New one on me, then again fords always had starting probs, head down now.

 

[Pudsey Bear]

Fix Or Repair Daily.

 

[davef]

Perhaps the easiest solution may be to uprate the wiring and fuse to handle 100 or 125 amp, the split charge relay is rated at 140amps.

 

[trevskoda]

Perhaps the easiest solution may be to uprate the wiring and fuse to handle 100 or 125 amp, the split charge relay is rated at 140amps.

Cheap as chips

 

[davef]

I see Amazon has this Renogy 20A dc to dc charger on offer at £74.099. Are they any good?

Amazon.co.uk

About the same price as uprating cables and fuses.

 

[1 Cup]

Have to get a mega fuse and switch for when started at 100 or 200 amp. Plus 35 mm wire But I have 30amp b2b
2 x 30 amp fuses still be 30amp in my head.

 

[trevskoda]

Have to get a mega fuse and switch for when started at 100 or 200 amp. Plus 35 mm wire But I have 30amp b2b
2 x 30 amp fuses still be 30amp in my head.

One at each end of battery to battery cable via the relay, alt will switch or like mine a small dash switch, can also be used for jump bust start from less batts.

 

[merl]

I have just replaced the alternator on my mk3 Transit. Noted it wasn't activating the split charge relay to charge the leisure battery, and found the inline fuses had blown - I put 2 of 30amp fuses in parallel. I assumed there must be a short in the wiring and checked this out, but there doesn't seem to be a wiring fault. The alternator is 70 amp, but cann't see all the power going to the leisure battery, but then it occurred to me once the voltage is high enough to trip the relay, the twin starter batteries are connected to the leisure battery which could allow a very high current if the leisure battery was low. 60 amp is probably the maximum the wiring would take, so cann't just increase the fuse size. Should I just carry spare fuses for when this happens, or is there a way of limiting the current? Or is this an inherent problem with split charge relay set-ups and why battery to battery chargers are better?

Quite a bit to decipher here. You say you have 2 30A fuses in parallel, I take it these are in the charge circuit between alternator and leisure battery?

 

[davef]

Yes the 2 x 30A fuses in parallel to give a 60A rating are just after the starter battery cabling to the split charge relay. The starting batteries are connected to the leisure battery via the split charge relay. Once the relay is activated when the alternator drives the starting battery above about 13.7v, in effect, all batteries are connected to the alternator output.

 

[Pudsey Bear]

This is the one I was recommended to use, it can be adjusted to cut in and out as required and dead easy to fit.

Fridge 12v relay ?

I'm fitting a Dometic RM123 three way fridge, the 240v connection is straight forward as is the gas - the 12v had me stumped as it (as I understand) requires a relay (?) from the battery to the fridge, are all relays the same or do I require a certain type ? 😮

motorhomebuilder.com

 

[merl]

Yes the 2 x 30A fuses in parallel to give a 60A rating are just after the starter battery cabling to the split charge relay. The starting batteries are connected to the leisure battery via the split charge relay. Once the relay is activated when the alternator drives the starting battery above about 13.7v, in effect, all batteries are connected to the alternator output.

OK, I guessed so but wanted to make sure before any further advice.
Blowing 2 X 30A fuses in parallel is no mean feat, with a typical MH install the charge wiring is 1X6mm or 2X4mm cables the cable length is typically quite long and passes through the control panel, relays, connectors and at least one other fuse in the control panel which is usually 30A, there is often a second fuse adjacent to the battery. ALL of this wiring resistance typically means that even when charging a relatively flat leisure battery there isn't sufficient current to take out the 30A fuse.
IF your alternator blew because it's internal regulator failed then that would lead to a much higher charge voltage (more than 14.4V) this would lead to a higher current flow too but alternatively the alternator could have failed because it was being asked to charge 3 pretty flat batteries at the same time through pretty hefty cables, and the engine wasn't much above tick over for a prolonged period, I'm assuming the leisure bat charge circuit must be quite short and/or heavy cables as it took out a 60A fuse?
Anyway all of the above said you really need to limit the current going to the leisure battery in future just as you say. You can do this by increasing the resistance in the charge circuit by using thinner cable or longer cable so opposite to what you'd at first think, you'd really need to own a DC current clamp meter to check things out, otherwise you'd be guessing at the charge current.
The Renogy B2B would be my choice. IF it's like the Renogy B2B I have (40A unit) it has the ability to toggle the unit to half power so you could fit a couple of toggle switches on the dash, one in the D+ and one in the 1/2 power toggle and you have the ability to make the B2B give you no charge, half power or full, this could prove handy if/when the alternator is already having a hard time charging the 2 vehicle batteries.

I've just had another thought. Maybe the 2 fuses blew because the split charge relay is defective and closed during cranking, this would draw a high current FROM the leisure battery and take out the fuses.

 

[trevskoda]

I've just had another thought. Maybe the 2 fuses blew because the split charge relay is defective and closed during cranking, this would draw a high current FROM the leisure battery and take out the fuses.

Hence i have a manuel switch so the alt can bring up the starter batt before i switch in the les batts, if i dont on my van the alt belt slips and squeels, have broken one belt in 10 years, to much strain on the alt, esp if you use a auto kick in, better a switch/relay setup.

 

[Thistle]

@davef
yes you have discovered one of the many down sides of using an archaic inefficient split charge relay
excessive initial input current into a heavily discharged battery typically requires expensive over rated cabling and fusing for a worthless few seconds or minutes then it rapidly drops to inadequately low current because the alternators already relatively low voltage through typically inadequate cabling most kits include, leads to volt drop and hence a very slow charge rate.

bloody useless things for charging batteries properly and efficiently taking many hours to do the job. They work fine in service vehicles etc where the batteries are at 100% all the time but not in situations where batteries are being heavily discharged.

most of the split charge setups I work with are wired and rated at 250-300A just to allow for the few seconds of extreme current pulled from the alternator and chassis battery combo.

Your alternator is a surprisingly low rating it would have been worth replacing it with a higher output unit, but bare in mind the chassis battery is also contributing current so yes dead easy to pop an inadequate 60A fuse into a heavily discharged battery.

if you are stuck with inadequate cabling then best fit a b2b

A safe rule of thumb is to size a B2B at a third to half of an alternators rated output so with your existing cabling and alternator I would suggest you buy a 30A b2b which will be capable of charging any target battery chemistry properly.

the Victron Orion is nice but quite expensive a refurbished Sterling bb1230 bought direct from Sterling would be good value.

Alternatively if you don’t have solar yet and or would like to benefit from bidirectional charging the Renogy DCC30S is a brilliant bit of kit once you account for its quirks

hth.

 

[davef]

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.

 

[yeoblade]

I see Amazon has this Renogy 20A dc to dc charger on offer at £74.099. Are they any good?

Amazon.co.uk

About the same price as uprating cables and fuses.

I fitted a 30amp B2B Renogy, fitted last summer (Also MPPT Solar) Brilliant kit and not overpriced like a lot of the other stuff, the app isn't amazing but shows all the basics, however if you are just wanting batteries charged and don't feel the need to spend hours on looking at and analysing charge rate data etc, Renogy the way to go

 

[merl]

@davef
yes you have discovered one of the many down sides of using an archaic inefficient split charge relay
excessive initial input current into a heavily discharged battery typically requires expensive over rated cabling and fusing for a worthless few seconds or minutes then it rapidly drops to inadequately low current because the alternators already relatively low voltage through typically inadequate cabling most kits include, leads to volt drop and hence a very slow charge rate.

bloody useless things for charging batteries properly and efficiently taking many hours to do the job. They work fine in service vehicles etc where the batteries are at 100% all the time but not in situations where batteries are being heavily discharged.

most of the split charge setups I work with are wired and rated at 250-300A just to allow for the few seconds of extreme current pulled from the alternator and chassis battery combo.

Your alternator is a surprisingly low rating it would have been worth replacing it with a higher output unit, but bare in mind the chassis battery is also contributing current so yes dead easy to pop an inadequate 60A fuse into a heavily discharged battery.

if you are stuck with inadequate cabling then best fit a b2b

A safe rule of thumb is to size a B2B at a third to half of an alternators rated output so with your existing cabling and alternator I would suggest you buy a 30A b2b which will be capable of charging any target battery chemistry properly.

the Victron Orion is nice but quite expensive a refurbished Sterling bb1230 bought direct from Sterling would be good value.

Alternatively if you don’t have solar yet and or would like to benefit from bidirectional charging the Renogy DCC30S is a brilliant bit of kit once you account for its quirks

hth.

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