Battery to Battery chargers (B2B) and Solar Power?

[arthur49]

Just to complete the picture, if you're interested, I have 2 x 100Ah batteries (can't recall make but sealed lead acid cheapos from EuroCarparts from memory) about 3 years old. They appear to hold their charge well ..... fingers crossed!

 

These are connected to each other and the 12v electrics by a 4 position switch (like this https://www.amazon.co.uk/Position-Battery-Isolator-Change-Switch/dp/B00R1CEHBS/ref=sr_1_14?ie=UTF8&qid=1466955705&sr=8-14&keywords=marine+battery+isolator+switch). In this way when off hook up I can choose, one or other, or both batteries and I can recharge them individually or together by B2B or EC155.

 

B2B, leisure batteries and starter battery are connected using 25 sq mm cabling (gold fuses). 100w (maybe 120w?) solar panel connected using 10 sq mm cable (fused) with regulator adjacent to battery boxes.

 

Ye May Gang Faur and Fare Waur

 

:-D :-D

[aandncaravan]

Arthur, you may know this already, but we are seeing a number of vans with Solar who think they have good batteries until they try to use them in anger.

 

What happens is the battery slowly deteriorates but it is not noticed because the Solar is constantly putting back the power that is bleeding out. Any checks on the battery voltage in the short term show a healthy voltage, because it has just been charged.

 

If you disconnect Solar and isolate the batteries they should stay charged for about 4 weeks minimum without losing any significant voltage.

Some are finding that the batteries are down well below 12.5v, in days.

 

 

There was a post recently from someone on here who was suffering from the battery not lasting the evening. Lost lights, etc when the system no longer had enough power to stay on.

He did the standard test of charging it fully and then placing a fixed load on it and monitored the battery voltage.

The battery passed the test, but still died part way through the next evenings use.

 

He charged it, left it for 2 weeks, came back to find it was dead, confirming what he thought, that it was expired.

A duff battery can sometimes deliver the goods if freshly charged and the loading is light, but ask it to work a bit harder and the voltage drops like a stone.

 

This is the point at which the charging systems are at risk.

 

I mention this because of the batteries you say you have? Most budget batteries are well down on efficiency before 3 years are up. Some of the nasties, less than 18 months. On a B2B I would have guessed that would be less?

 

 

[arthur49]

Thanks Allan, I'll check the batteries tomorrow

[StuartO]

arthur49 - 2016-06-25 9:47 PMWell for what its worth aandncaravan I enjoy and value your posts .....

 

And so do I.  Keep up the good work and don't be discouraged by grumpy criticism.  Having bought a gadget, some of us have to insist that it was a good buy come hell or high water and when that happens you need to recognise what's happening and take them with a pinch of salt!

 

[Tracker]

I'll add my appreciation of Alan's contributions too, please carry on the good work.

 

Sometimes in life, as many of us continue to discover, the reality of practical use particularly of electronics does not quite match up to what the theory predicts.

 

Is this because systems that were never designed to work together are unable to communicate properly to enable them to work together as expected - or is it part of a wider conspiracy to usurp the laws of physics and take over the planet when we are all asleep!

[Robbo]

Another +1 for Allan's contributions, always makes for interesting reading from a practical and real life experience perspective.

 

I've been test driving my 2 x Varta LFD90's installed in February and after a trip to Spain, am very happy with the performance. So, thanks again Allan for the recommendation :-D

[veletron]

Hi

 

This thread seems to have kicked off since I was last here!!!

 

Lots of marketing BS on the Sterling power website re B2B's!

 

Its a well known fact that alternator charging may not put the optimum voltage into a battery. For a car battery, that cycles between maybe 70% and 90% of its total capacity, this simply does not matter. For a leisure battery however that last 10% (given that its good not to run them down below 40-50%) is pretty handy - as ever the effectiveness of the charging system on your van depends on how it was implemented - some are much much better than others.

 

On my Tribby, I measured just 14.2V and a max charging current (when starting up after a night watching the telle in winter with the diesel heater spinning), of just 15A. Given that I had three 85AH LB's in that (to keep the darned diesel heater working in mid-winter), The LB's would require hours and hours of driving to recharge. On the Tribby, this was partly to do with the wimpy-wiring to the LB's. The voltage of just 14.2V meant that it was near impossible (eg would need a week of driving) to get to 100%, the charging current dropped off to a couple hundred mA once the batteries neared ~90%.

 

Enter a Sterling B2B to replace the Tribute supplied system. The bulk voltage rose to 14.8V, the B2B does this by sensing a charge from the alternator to the van battery, and then stepping this up using a switched mode PSU to 14.8V. I wired this in with some decent 4AWG welding cable, and AGM reset-able electronic fuses. Result was 40A to the leisure batteries, and the higher voltage enables higher currents to be pushed into the leisure batteries as they near the end of their charging cycle. As such, I was still seeing 10A to the batteries as they approached 100%

 

After a period of time determined by the voltage and current mix through the B2B, it drops the voltage to 13.8V (float charge) and keeps it at this level.

 

Fast forward to my new van, and the charging system is better. The cables bigger and the batteries closer to the alternator. This meant that I saw 14.4V at the leisure batteries. That 0.2V difference might not sound like much but makes a huge difference for charging efficiency.

 

I was seeing 30A to the leisure batteries at 14.4V, the higher voltage also meant that the top-off charge (eg getting beyond 90% SOC) was more likely to come in reasonable time. I almost did not fit the B2B, on the new van, but 40A in my book is better than 30A, and I also liked the float charge at 13.8V - basic alternator charging has no such option.

 

I disabled the built in system and put the B2B back in its place together with a NASA BM1 voltage/current/soc/AH counter meter - a superb piece of kit.

 

So... is a B2B worth it?? Go measure the current to half-dead leisure batteries, and then when they are more fully charged, go measure the voltage at the LB's (with the engine running, obviously!)

 

If the current to the half-dead leisure batteries is under say 30A, you would benefit from a B2B or simple replacement charging system described below. Ditto if the voltage when nearing full-charge is < 14.4V

 

A far cheaper option to the B2B for poorly wired vans is a length of 4AWG welding cable and a voltage sensitive relay. Just wire this in via a fuse direct from the van battery to your LB's (remembering to disable the vans built in charging system), and you will see 90% of the benefits of the B2B with none of the negatives and save yourself a pile of cash. With the new van, if I did not already have the B2B then I suspect this would have been my route. When I sold the old van, this is exactly the system that I put in it in place of the sterling B2B.

 

In terms of negatives of the B2B. In Summer, my solar panels mean the batteries are almost always charged when I start the engine. however when the B2B kicks in, it feeds 14.8V to the leisure batteries! This is a serious weakness - the B2B should sense that the LB's voltage it way up at 14V (due to solar charging) and start in an idle state while monitoring the leisure battery voltage. On mine, it can apply that 14.8V for the 1st hour or so of driving (manual says it does it for 4 hours - it doesn't!). The current taken is tiny, couple of hundred mA, but even this will make the LB's gas. After an hour it drops down to 13.8V for the remainder of the journey, but stop and restart the engine and its back to 14.8V again! Its a weakness, and one that will shorten the life of the batteries, but given the way amount I use my van, always off-grid, often in winter, if I get 2 years I consider this to be 'good'. Your mileage might differ!

 

4AWG might seem like overkill - but the aim here is to reduce voltage drops over cable runs, A long cable run of 8AWG carrying 30A will lead to a loss over the cable length. This loss could be half a volt depending on the run length. Half a volt is simply massive when we are talking about battery charging! If in doubt, over-rate your cables!

 

Will a B2B help you? - it depends...!

Will replacing the existing charging system with a voltage sensitive relay help you? - it depends...!

 

If you only ever do occasional wild camping/winter wild-camping and are mostly on hookup then you don't need to worry about any of the above - just enjoy your van as the manufacturer delivered it!

 

Nigel

[arthur49]

Interesting Nigel thank you

[Alanb]

This thread was current when I was on a trip trialling my B2B installation, which is CTEK D250S DUAL engineered to connect around a cbe DS520AN / PC200 system. However I had extremely limited internet connectivity, and was unaware of the thread.

 

Some interesting reading on my return home. Thanks to all contributors.

 

The D250S has a more appropriate output for 160 Ah of Banner batteries in my PVC, than some of the larger Sterling or similar units. Also after some re-arrangement I managed to find space for it within 2m of one of the batteries. This allowed the battery temperature sensor to be attached without extending the connecting cable.

 

Has anyone got any suggestions for fixing the temperature sensor to the battery? I settled for a short length of Duck tape, which is easily removable.

 

So far I have seen 20A at tick-over, and on site it took several hours for the battery voltage to drop to 2,6V, so I am pleased with the results. (Load includes LED lighting, radio, fridge control, and small computer.)

 

I have noted that the D250S continues working after stopping the engine. That is until the vehicle battery drops to 12.8V. I will be watching this!

 

The D250S includes a MPPT regulator for a solar panel, for which I have run cables, but have yet to decide upon fitting. The D250S provides solar charging for the vehicle battery, after charging the habitation battery, but the vehicle battery charge is routed via the same cable as the alternator input. It is not therefore possible to adopt Allan's suggestion of a D+ type controlled to the D250S if vehicle battery solar charging capability is to be maintained.

 

Grafting the D250S around the cbe system requires re-routing the fridge supply as well as interrupting the input to the D250S when the mains charger is operating.

 

Supply cable to the D250S is 6mm, but from there to the battery I have increased to16mm, in order to reduce voltage drop and improve battery voltage regulation.