Split charge relay issue/challenge (design not fault)

[activecampers]

Hi
Quick background: Van has 2x leisure and 1x vehicle battery, all same spec/age (Varta S4 I think) - all new. Previously I had installed a VSS off the alternator feed which powered a separate (non intelligent) split charge relay for battery and fridge. This worked fine for 7+ years. (previously, builders of van didn't have a VSS or intelligent switch).

Anyway, due to relay failing, I've replaced it all with an intelligent split charge relay, battery-to-battery. Which, when battery voltage >13.6 (ish) it turns on connecting leisure batteries and fridge. Standard stuff. But 2x issues

1 - The relay was a bit "slow" in turning off, so connecting fridge/batteries for a bit of time after engine off. So adjusted voltage switchover point a bit. Now though, relay clicks "in" - then as fridge/batteries take power, it drops it below the cutover voltage so the relay clicks off. Then on. Then off a couple of times till it keeps the voltage in.
(It seems to be a bit too quick changing state whereas if it allowed the voltage to settle for 5-10 seconds it'd be fine - also seemed better when taking voltage from alternator direct, but I don't want to do this I'd rather take it from the nearby vehicle battery)

2 - If the leisure batteries are low, and the fridge is on, then the 30A relay fuse I installed blows. If fridge is off, then its fine, then wait 30 seconds and put fridge on - fine. Its the "initial draw" of power that spikes over 30A and blows fuse.
Now wiring to split charge relay is fused at 30A. Fridge is 10A (and heater checked), and leisure batteries fused at 25A. Yes, I could put in a 35/40A fuse but that's not the point lol! (For last 8 years, there wasn't a fuse before the relays, jus after, and all fine - so maybe me fusing at 30A is a bit pedantic).

So is there a more intelligent split charge relay, that will (a) delay switchover to/from for a few seconds to allow voltage to stabalise on state change; and (b) limit current to leisure batteries?

Cheers

(Edit: The relay spec installed now seems to say "on" at 13.5 "off" at 13.2 which is a bit tight which may explain issue (1) above. Probably need/want one at, say, "on" at 13.7 and "off" at 12.9 - or even 14.0/13.0..... )

 

[activecampers]

Aha!
Something like http://www.12voltplanet.co.uk/victr...sitive-relay-battery-combiner-1224v-120a.html sounds okay and has the "intelligent" voltage control to intelligently "smooth" fluctuations. But of course, doesn't do the fridge. If only it was double throw....
/back to google

 

[activecampers]

Hmmm.
Reading more about the Victron Cyrix-ct Voltage Sensitive Relay - its bi-directional. That'd be useful - e.g. on hookup it charges the engine battery too - that'd be really good....

And thinking about it, I didn't want to use the alternator feed wire for the split-charge relay as the relay seemed to feed back - and I had an instance of turning off the igniton and the van still running.... But, this feed was ORIGNALLY used to charge both the leisure batteries AND run the fridge, so using one of these Victron relays for the battery charging, the fridge would be OK by itself off the alternator feed and fused accordingly so a lot safer and neater.

I think I'm happy with that...!

 

[andy63]

hi didn't manage to get my head round everything you were saying above ,but just to give you my take on a vsr....
I have one installed between vehicle batteries and the leisure battery bank.... more or less doing the same job as a bat to bat charger all be it not quite as efficiently..... the relay will connect the two battery banks when either side is at 13v for 2 min or 13.6 v for 30 sec...it disconnects the banks when either side is at 12.35v for 10sec or 12.75 for 30 sec.....
its not uncommon if neither of the battery banks has a load on it to drop the voltage for the relay to keep the battery banks connected for some time , and im talking an hour or so easily... with a small drain from the leisure battery bank to the vehicle battery of up to an amp..
its a blue sea 120 amp vsr.....so really just saying that its not uncommon for vsr to keep connected for some time with no load on the batteries
ta andy

 

[activecampers]

Hi Andy - what conversion do you have?
As for Blue Sea - I was just on their site and saw https://www.bluesea.com/resources/527 which gives an interesting reason for my question in part (1) .
Good point made about it not being an issue if all batteries connected for an hour - you are right - though one exception? If its still connected and you try and start the van and it pulls the power for the starter motor over the relay....
If I relocate the fridge off the current Voltage-sensitive split charge relay wired to the alternator feed, then my "possible" issue of the fridge taking power from any battery is negated and as you say it would matter not if all batteries are connected together except starting...
Hmmm

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[andy63]

If its still connected and you try and start the van and it pulls the power for the starter motor over the relay....

check the specon the blue sea relay...it disconnects on start up I think....mine does

my conversion is on a mwb mk7 high top transit..nothing plush but suits me....
ta andy

 

[activecampers]

Thanks, will check - how would it know? Will enquire....

My conversion is a swb mk6 transit with high roof - plenty good enough for us!

(edit: The blue sea one needs a wire to the starter motor/crank and uses this to isolate leisure batteries. Thinking about it, the low-voltage detection may do the job - also I'm aware that the "builders" of the van linked wires so the leisure batteries were linked to the vehicle battery on ignition on - so probably not that big a deal. Will keep reading.. Ah - the relay I'm on about, disconnects instantly on v<11v - so on crank I guess V drops that low, and hence disconnects.)

 

[jonandshell]

You are trying to cure a non existent problem!

The starter battery is not being drained by the VSR. A fully charged battery is 12.7 v, the higher voltage keeping the relay closed is just post charge surface charge.

As for the initial inrush of current, have you tried thickening your cables and upping the fuses? If the VSR is not up to the current expectations, simply use a heavy duty relay switched, as before from the alternator d+ terminal.

 

[activecampers]

The problem I have "today" does exist - with the relay switching on and off. The VSR linked, has a timeout - so >12.8v "closed" 12.4-12.8 - "3 mins closed". So it would totally solve the switching issue, but may bring in the "restart" issue (or indeed starting when on hookup when relay is closed - not something we'd ever do deliberately).

The cables I'm using now are 50A cable, whereas it was, I believe, 20A/25A. The fuses the builders used and thus the wires I can't get to, are 20A/25A - so I've just upped the cables where I can - and as I never had issue with 20A/25A cables/fuses then that shouldn't be the issue.

Maybe the bigger cables are allowing more current draw and introduced the problem lol!

The VSR now is a, cough, cheap 30A one I picked up at short notice. So I've no issue binning it and if I do happy to up the fuse to 35/40A which may fix the initial current spike. But not with the crappy VSR that's there now.

All batteries are close, so would prefer to access power directly off the batteries.

So a >30A VSR, with a longer delay (or lower disconnect voltage) would be fine - 13.5/13.2 on the current relay is a bit poor. Just trying to see whats available to replace it with