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spruce

Split Charge Relay.

 

Most window cleaners who use the Water Fed Pole with a van mounted tank will, sooner or later, question whether they need to add an auxiliary charging method for their leisure battery that’s driven from the vehicle’s alternator or not.

 

A Split Charge Relay (SCR) is now a standard towing accessory in the caravanning and motorhome (RV) leisure industries, so we as window cleaners have a well trodden path to follow. But what is a SCR and how does it work?

 

Some manufacturers call these relays separators, which is perhaps a better description as they keep the vehicle’s starter battery and the leisure battery separate or isolated and only link them together when the vehicle’s engine is running. So their purpose is to preserve the charge in the starter battery whilst current or power is being drawn from the leisure battery. This means that if all the power from the leisure battery is drawn (it’s now flat) there will still be a full charge in the starter battery to start the vehicle’s engine.

The original SCR’s were basically standard relays. Over time a Voltage Sensing Relay (VSR) or an Intelligent Split Charge Relay has become the most popular to fit. It is a little simpler to fit and it is activated via voltage sensing electronics inside the relay. 

 

Some window cleaners advise that once they have fitted an SCR or VSR they haven’t needed to supplementary charge their leisure battery since. Others aren’t as fortunate and do need to top the charge of their leisure batteries up periodically. The frequency of supplementary charging would very much depend on much power is being drawn by the system and how much mileage is driven a day.

 

A justifiable assumption is that most Shurflo or equivalent water pumps will draw about 4.5 amps each hour they are running if being controlled by a mainstream controller. Obviously a window cleaner working 8 hours a day won’t be running his pump for 8 hours. Actual pump running time will vary from one window cleaner to another and is very dependent on the makeup of his round. It will also differ from day to day. Current draw will increase with a second operator and with any additional accessories such as a diesel heater or electric hose reel.

 

A window cleaner will be able to estimate how many amps he has drawn from is battery by estimating how many hours a day the pump/pumps has/have worked. In our experience we have settled on about 50% of time on residential cleans and in the region of 80% on commercial cleans with a large number of windows. So in theory this means that if I run my pump for 2 hours and use 9 amps (4.5amps x 2) then it will take about an hour of charging the battery to replace that charge at 10 amps.

But in reality, it takes longer. The reason is that the fuller the charge in the leisure battery the less charge the leisure battery will take. It has been likened to a sponge; the more saturated it is with water the less it will absorb. I once read in a split charge relay guide that it would take a journey of 750km to fully recharge a flat leisure battery in an RV.

 

 

Numax, who are manufacturers and suppliers of quality leisure batteries, advise that a leisure battery shouldn’t be charged at a rate higher than 10% of the battery’s capacity. So a 110amph leisure battery shouldn’t be charged above 11 amps.

 

Drawing 9 amps from a fully charged 110amp leisure battery will mean that the battery has 101 amps remaining (110 – 9 = 101.)

 

Letting a starter battery go flat will damage it whereas a leisure battery will tolerate going flat more often.  So one of the descriptive terms of a leisure battery is a Deep Cycle Battery and the specs will usually advise how many deep cycles the battery should handle. However, a leisure battery will give better service if the battery is fully recharged as soon as possible. It is also recommended to never let a leisure battery drop below a 50% charge. This is worth noting as more and more leisure battery manufacturers refuse to give warranty on leisure battery used by window cleaners as we abuse them due to the nature of our demands on them.

Modern vehicles all use alternators to charge the battery. Even if the alternator has to supply current to other accessories, ie lights, the alternator will still charge the leisure battery at the same rate. It makes no difference if you are driving down the motorway or stood idling at the traffic lights. So whilst getting stuck in a traffic jam is very frustrating, it’s good for your leisure battery.

 

Battery to Battery chargers.

 

Vehicles manufacturers are being forced by emission regulations to become more environmentally friendly. This has meant that there is a real possibility that vans registered after 2015 are likely to have smart alternators, stop start and regenerative charging.

 

A conventional Voltage Sensing Relay will not work on these vans, especially if they have regenerative charging. Regenerative charging is simply a system that recharges the battery when a vehicle is decelerating. The van’s ECU will instruct the alternator to charge the van’s starter battery until it is 80% full. It then leaves the remaining 20% to be charged when the vehicle is decelerating on a downhill, braking or slowing down for traffic lights etc. The alternator then puts a high voltage current into the battery. To accommodate this, the battery is now a calcium battery as a lead acid battery won’t tolerate the high voltages. Alternators are bigger and battery capacity has also increased; in some cases both by as much as 100% or more.

 

Sterling Power Products have been in the forefront of auxiliary battery charging for many years. Their pedigree is from the ambulance service and the Marine industry. According to Sterling their Battery to Battery charger does NOT take current from the starter battery for charging the leisure battery. Rather is uses alternator power to charge the leisure battery. (A ‘smart’ alternator still puts out a nominal voltage of 12.4v so it’s ready to dump a large charge into the starter batter at a moment’s notice. But 12.4v isn’t sufficient to charge the battery. So the Sterling Battery to Battery charger uses that 12.4 volts from the alternator and boosts it up to 14.4 volts which then charges the leisure battery.) There is a wiring schematic included in the pack to accommodate different charging modes. When the regenerative program activates, the battery to battery charger also regulates the voltage of the alternators output so it doesn’t damage the leisure battery. (Under regenerative charging the voltage can reach 15.5v on Ford vehicles and as high as 17.0v + on Renaults according to Sterling. Charging a lead acid battery at these voltages will cause gassing and premature lead acid leisure battery failure.)

 

A battery to battery charger is much more expensive than the old VSR but as demand increases then they should become cheaper to buy as ‘mass’ production reduces manufacturing costs as does manufacturer competition.

Currently the Sterling BB1230 seems a pretty good buy.

https://sterling-power.com/collections/battery-to-battery-chargers/products/2015-battery-to-battery-chargers-non-waterproof-drip-proof-ip21

At the time of writing (May 2017) they are available via an Ebay supplier for £200.00 with free postage.

 

These B2B chargers can also be used as replacement for the VSR on older systems and, according to Sterling, will do a better job at charging the leisure battery.  Conventional alternators are brilliant at supplying all the power a vehicle’s owner needs, eg., lights, windscreen wipers, radio etc. But they aren’t good battery chargers.

 

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Edited by spruce

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kevinc250

bruce,thats probably the best descriptive answer to our charging needs i've read over the years,strangely because i understand the maths etc it makes perfect sense,sterling are very good and i phoned them a few months ago about my new stystem and charging needs and were very helpfull,yes the relays sound expensive for the moment and when i buy a newer van then this option would be the only option-hopefully prices will have come down by then????????.

i don't need the b2b charger at the moment so opted for a durite and an onboard 200ah mains charger with two 100ah batteries installed in series parralel,this is because as you know i'm installing a small deisal heater soon so the extra amperage will cope with the load on initial pre-heating,whilst the durite will cope with the amperage loss-hopefully lol.

i hope the mods would/could make this a sticky as its long overdue and would help many many people in there choice with on board chargers

 

 

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spruce
5 minutes ago, kevinc250 said:

bruce,thats probably the best descriptive answer to our charging needs i've read over the years,strangely because i understand the maths etc it makes perfect sense,sterling are very good and i phoned them a few months ago about my new stystem and charging needs and were very helpfull,yes the relays sound expensive for the moment and when i buy a newer van then this option would be the only option-hopefully prices will have come down by then????????.

i don't need the b2b charger at the moment so opted for a durite and an onboard 200ah mains charger with two 100ah batteries installed in series parralel,this is because as you know i'm installing a small deisal heater soon so the extra amperage will cope with the load on initial pre-heating,whilst the durite will cope with the amperage loss-hopefully lol.

i hope the mods would/could make this a sticky as its long overdue and would help many many people in there choice with on board chargers

 

 

 

Thank you.

@Green Pro Clean Ltd suggested it would be a useful addition to the tutorials and asked me to consider writing it a while back. Its finally been completed.

What does intrigue me is the disparity between what Numax said to me and what Sterling say. There is a video that features George Sterling hooking up his Range Rover charging system to his caravan. He shows that he is charging his van batteries with around 30 amps using the B2B charger. If he removes the B2B charger and uses the electrical charging system it only a couple of amps.

 

Now if he is pushing 30 amps in a 110 amp leisure battery that 3 times more than Numax suggest.

 

I had even considered buying one in a moment of weakness and experimenting with it.

 

 

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kevinc250

i've forgotton ohms law now bruce as i learnt it so long ago,i had more hair then and it was a different colour instead of the grey it is now,i'd  have to look at the vid a few times to understand it more  i think but initially you would think resistance in the circuit and battery would play a large part in his experiment?,i could also be very wrong but ohms law is well,ohms law

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spruce

@kevinc250. I was going to mention that the Durite VSR is bi-directional. So if you rig the mains charger up to the leisure battery the VSR will activate and top up the starter battery as well.

 

I put an on/off switch on the earth of my VSR (it's the same unit but rebadged) so I can switch the unit off totally if needed. I have found it a worthless addition tbh, but if I ever need to remove the leisure battery and drive the van I can switch the VSR off.

 

What I would consider doing in the future is to add another inline relay that bypasses the VSR. It would help to have a switchable option of a connection between the leisure battery/batteries and the van's starter battery during starting. In the past 4 years I had 2 starter battery failures and could have done with a boost from the leisure battery to get the engine started. (The first failure was the original battery and the second was its replacement. I managed to jump start the van the first time as I was parked on a downhill but had to call the mrs out to jump start the van the second time from her car.)

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kevinc250

another relay would be a good option-hopefuly never needed but i think i'll consider this for the winter time,i have a snapped glow plug whilst its not caused an issue yet the relay idea could get me out of a tight spot

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spruce
1 minute ago, kevinc250 said:

i've forgotton ohms law now bruce as i learnt it so long ago,i had more hair then and it was a different colour instead of the grey it is now,i'd  have to look at the vid a few times to understand it more  i think but initially you would think resistance in the circuit and battery would play a large part in his experiment?,i could also be very wrong but ohms law is well,ohms law

 

I know the feeling. Mind you I started to grow grey when I was 11. It started with a small patch on the side of my head and just spread. TBH it didn't bother me and I just don't understand why the wife would rather be seen dead that to be seen with a grey hair.

 

I fitted a standard split charge relay to my Suzuki Van and added the additional towing socket to charge my leisure battery on the towbar of my original trailer system. The voltage drop was a dramatic as George's video shows on his Range Rover. Sometimes I wonder if there is a bit of sensationalism added to the video for a greater sales impact.

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kevinc250

never knew the durite was bi-directional thank you for that bruce

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spruce
9 minutes ago, kevinc250 said:

never knew the durite was bi-directional thank you for that bruce

 

Th other thing I noticed was that if the leisure battery is fairly fully charged the VSR takes quite a while to isolate the leisure battery. I've seen a small discharge (3 to 5 watts) from the van's battery to the leisure battery for 10 - 15 minutes.

 

However, the moment you put a load on the leisure battery the connection breaks. It remains connected when the voltage on each battery is high and only disconnects when the voltage drops as it stabilizes.

Edited by spruce

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kevinc250

i've also forgotton the wattage calculation mate although the triangle with the letters are still somewhere in my fully blocked memory,i wonder if both main and stystem batteries were the same type if the discharge would appear?

maybe the small discharge is down to the type of battery (leisure)and voltage equalising?-its been a long time some 32 years since i visited all this battery malarky and the old grey cells are a bit rusty

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