split relay kits 30amp v 70amp

[philgb]

Hi all, first post and converting our citroen minibus up. Planning the electrics at the moment and looking at split charge relay kits on fleabay.
A 30A kit is £17 and another is a 70A kit which is about £70 both seem to me to be up to the job!, but for the price gap.
Q. Is the 30A kit suitable to link to a 110 amp leasure battery, both kits come with fuses at either end of the cable run using 4.5m cable. Or do you need 70A?

Will have a 12v fridge running during journeys

 

[Firefox]

30A should be enough.

Try to use a 20A or 25A fuse with say 40A cable. Some kits recommend 15A fuse but if your leisure battery gets very flat, that can quite easily get blown. I have replaced quite a few 15A fuses on people's vehicles.

An alternator on a big diesel engine can easily kick out 30 amps for a few seconds but usually it will be charging at 5-10 amps or so when the leisure battery voltage builds up a bit.

Fridge usually goes go on a separate relay/circuit so shouldn't come into the equation unless the relay has a fridge take off, in which case it's an extra 5-8 amps, when the fridge is on.

 

[shaunr68]

I installed one of these, with cable rated at 140 amps and a 100 amp fuse at each battery. Just IMHO I think a 30 amp relay will be woefully inadequate and will tend to blow the fuse due to a high initial surge on a heavily discharged leisure battery.

 

[oldish hippy]

how would igo about charging up a second lesuire battery that is not the same amperage as the first one yes ido understand that they realy need to be same amperage all iwish to do is to charge it and then disconnect it and use it till it needs charging again#

 

[Firefox]

The 30A should be OK if you just discharge your leisure battery about 50% and don't let it drop below 12v or so.

This is good for the battery life.

Some people have a habit of draining their battery right down, in which case your battery may not last too long. Less than 30 cycles?.... but also you may well blow your relay fuse on start up, if it is only 15 or 20 A. Still, fuses are cheap and if you take care, and are ready to replace the odd fuse the cheapo system should work OK.

 

[philgb]

thanks for the info

Cheers for the replies, will go for the £17 kit

 

[Deleted member 951]

..................Some people have a habit of draining their battery right down, in which case your battery may not last too long. Less than 30 cycles?.... but also you may well blow your relay fuse on start up, if it is only 15 or 20 A. Still, fuses are cheap and if you take care, and are ready to replace the odd fuse the cheapo system should work OK.

I've been reading up on this recently Vernon, and there is a lot of conflicting information out there. But, many say that deep cycle batteries are designed to be completely discharged and should last for hundreds of cycles. I must admit over many years of boating and completely draining batteries, I usually got 3 - 4 years out of them. I also ran a boat on a car battery once and it lasted far more than 30 cycles after being discharged completely many times.

Is it a case of they don't make 'em like they used to?

 

[Tony Lee]

Is it a case of they don't make 'em like they used to?

Too many factors to generalise.

For a start - what type of battery - conventional flooded cell, sealed conventional, AGM, Gel and within these groups there is a vast range of price, quality and manufacturers recommendations.

For instance, if you run a battery "flat" and each time leave it discharged for a week, then the battery life will be much different than if you completely charge it up again immediately. Rate of discharge is another factor, as is whether you really do recharge it to close to 100% or just recharge it until the idiot lights claim that it is fully charged. Overcharging with resulting loss of electrolyte level to the extent that the plates are exposed is another big no-no. How are you charging? Cheap taper charger that may actually overcharge, split charging on the vehicle which often leaves the battery chronically undercharged, big Sterling DC to DC charger that might exceed the maximum allowable charge current (bigger is not always better), or quality three-stage mains charger. Discharge rates? Absolutely essential that cook prepares a three-course meal on the microwave operating off an inverter powered from a single 80 Ah battery? Then expect an early demise of the battery.

Then there is "luck" involved as to how long the battery lasts before it fails due to natural causes regardless of how it is looked after - and of course the biggest factor of all - people skite about how long their batteries last just to make others feel bad.

 

[Deleted member 951]

Too many factors to generalise.

For a start - what type of battery - conventional flooded cell, sealed conventional, AGM, Gel and within these groups there is a vast range of price, quality and manufacturers recommendations.

For instance, if you run a battery "flat" and each time leave it discharged for a week, then the battery life will be much different than if you completely charge it up again immediately. Rate of discharge is another factor, as is whether you really do recharge it to close to 100% or just recharge it until the idiot lights claim that it is fully charged. Overcharging with resulting loss of electrolyte level to the extent that the plates are exposed is another big no-no. How are you charging? Cheap taper charger that may actually overcharge, split charging on the vehicle which often leaves the battery chronically undercharged, big Sterling DC to DC charger that might exceed the maximum allowable charge current (bigger is not always better), or quality three-stage mains charger. Discharge rates? Absolutely essential that cook prepares a three-course meal on the microwave operating off an inverter powered from a single 80 Ah battery? Then expect an early demise of the battery.

Then there is "luck" involved as to how long the battery lasts before it fails due to natural causes regardless of how it is looked after - and of course the biggest factor of all - people skite about how long their batteries last just to make others feel bad.

Very hard to answer as it is a while since I had boats, but they certainly didn't have the charging systems that are around today. All I ever had on boats were simple split charging systems, sometimes with a tiny 10w solar panel for trickle charging. We used to go out on the boat every weekend and as long as the starter battery was ok, we knew that by the time we reached our destination we would have power in the leisure battery.
We were fairly ignorant of battery abuse back in those days and so we were probably on a wing and a prayer a lot of the time without realising it. We always assumed that the tiny solar panel was keeping us topped up, though in reality this was probably not the case.

Mind you, back in those days, all we needed electricity for, was lighting and occasionally a small TV. In all, I had 13 boats and I can only go by receipts or word of mouth from the vendor as to the age of the batteries, but as a rule of thumb, we used to expect 3-4 years.

To be honest, I am not technical enough on electrics to know the optimum setup and type of charger and battery, so I leave it to the experts to provide me with the best system, although, even the experts opinions conflict.

I see no mileage in 'skiting' though?