Is a B2B charger necessary?

[Full Member]

I guess this question has been asked before, but I couldn't find any reference to it, so I'd appreciate some guidance. My van has an 80 ah starter battery and 100ah leisure, with no solar. It is a basic 1992 Merc, with no alarms, engine management gizmos etc, no EHU and we do not have onboard fridge or hot water: the leisure battery simply provides lighting and radio but mostly charging our phones, tablets and vapes. The van is fitted with a split charge system with 140a VSR.
We have not had the van long enough to know if this is all we need to keep the batteries charged on any extended trips we may do: last year all was fine but was only short trips no more than 10 days, in the summer, but this year (hopefully) and next we will use it much more, for longer periods. I regularly hear reference to B2B chargers, and my question is should I have one, and why?
Whilst the van is parked up unused at home I use a portable condition charger with crocodile clips to each battery in turn

To get back to the original question!
As I've posted at #19, I have a 300W solar panel and a Victron 100/20 solar controller, dougbobbill.
Like you, I use very little electrical power (only radio, charging phone, led lights, gas fridge, gas blown air heating and gas hob etc) and for some years managed very well indeed with a single 90Ah leisure battery and no solar panel.
A couple of years ago I went to Spain for a large part of the winter and thought that I'd spend more time in one place - so fitted the solar system I've described. I also added a second leisure battery so that in total I now have about 200Ah of leisure batteries. That gave me the freedom to stay off grid for extended periods whenever I chose.
I don't have, never have had and don't plan to have a battery-to-battery charger.
I hope that helps you in coming to a decision that suits your moho use.

Colin

 

[in h]

We have not had the van long enough to know if this is all we need to keep the batteries charged on any extended trips we may do

My strong advice is to leave things as they are.
If the motorhome is 27 years old, presumably the previous owners found the power setup suitable.
If you add a B2B or solar panel now, you'll never know whether or not you needed them.
No, leave it as it is, and see how it goes when you get a chance to use it.
The prices of such things will fall in the inevitable economic crash that's coming.

 

[mistericeman]

My strong advice is to leave things as they are.
If the motorhome is 27 years old, presumably the previous owners found the power setup suitable.
If you add a B2B or solar panel now, you'll never know whether or not you needed them.
No, leave it as it is, and see how it goes when you get a chance to use it.
The prices of such things will fall in the inevitable economic crash that's coming.

This is possibly the one thing that most of us (myself included) that have posted so far have missed....

Folks needs and useages are so varied power use and wild camping etc...
The only person that will know WHAT they need is the person using the vehicle.

As above....

Get a few trips under your belt before deciding WHAT if anything you need/want to change.

 

[dougbobbill]

That's much appreciated info from everyone.
Taking it all into consideration I think we will do as suggested and leave it as it is for now. If I'm worried about it in the autumn/early spring then I'll consider £100-150 solar. B2B is really a bit too pricey for my old van.
Thanks to all for the kind input

 

[wildebus]

That's much appreciated info from everyone.
Taking it all into consideration I think we will do as suggested and leave it as it is for now. If I'm worried about it in the autumn/early spring then I'll consider £100-150 solar. B2B is really a bit too pricey for my old van.
Thanks to all for the kind input

What you SHOULD get if it is not already there is a way to keep an eye on the battery level. This can be as simple as a Battery Voltage Meter. Not perfect but a lot better than nothing.
Something like this you can plug into a 12V socket and take a reading: https://amzn.to/3ceVffK

Then compare the voltage to this chart and you will get an approximate idea what your battery charge is

take a note when the engine has not been running for at least an hour or vehicle not plugged into hookup.

 

[Markd]

As some others have said Feb to Oct in southern Europe (visas permitting ) should be a cue to installing solar.
In my view that would give a good return on investment.

 

[nabsim]

I wouldn't do anything until you know if you need it. Sounds like you have very low power demand so see how you go

 

[dougbobbill]

Thanks again. The battery voltage chart very useful

 

[Markd]

Batteries aren't all the same - some modern designs will be 50% discharged at 12.6v.

Try this Yuasa table that I've lifted from the site we can't link to.

 

[in h]

Please note that the voltage is only an indication of the state of charge if the battery has had no charging AND no load for at least an hour.

This has been said earlier in the thread, but so many people overlook it, that it's really important to stress its importance.

If you notice your battery voltage is lower than you'd expect one evening, chances are you haven't been sitting in the dark for the last hour.

 

[cronkle]

Interesting to read this thread. For years we have had just the two battery and split charge relay system with low use items (no TV while we are away). The latest van has blown air heating so during the winter we generally only get one night out of the system unless we use multiple duvets. I have been considering possible solutions and have come to the conclusion that my first step will be to fit a second battery to double our endurance.

We tend to move on a lot but during the rally/show season we often stay put for 4 or 5 nights with no hook-up. On those occasions we have a 120 watt portable solar panel which works for us. It's interesting how technology is creeping up on us; I remember years ago thinking how clever a split charge relay was.

 

[in h]

Interesting to read this thread. For years we have had just the two battery and split charge relay system with low use items (no TV while we are away). The latest van has blown air heating so during the winter we generally only get one night out of the system unless we use multiple duvets. I have been considering possible solutions and have come to the conclusion that my first step will be to fit a second battery to double our endurance.

We tend to move on a lot but during the rally/show season we often stay put for 4 or 5 nights with no hook-up. On those occasions we have a 120 watt portable solar panel which works for us. It's interesting how technology is creeping up on us; I remember years ago thinking how clever a split charge relay was.

Yes, blown air heating is quite a load. Truma reckon an average of 1.4A for the Combi 6 but I suspect it's a bit less than that turned down overnight.

Diesel heaters are far worse: not only do they have a bigger, more power-hungry fan, but they also have a fuel pump and they draw about 12A on every startup (and sometimes on shutdown).

The steady load of the heater drags the battery voltage down.

Typically a single 100Ah battery on a split charge relay or VSR will cope in a motorhome just running lights and water pump. Add a USB phone charger and you should be OK. A TV is OK if it isn't used much. Maybe.

It's when you add long term loads like a heater with fans, or a 12v-only fridge, or you add big loads like an inverter that the problems start.

1.4A average load from the heating doesn't sound much, but it's 33Ah per day. That's about the whole usable capacity of a 100Ah leisure battery running off a split charge or VSR system. You would need to drive for two or three hours each day to replenish it.

 

[in h]

Forgot to add: one way to save power is to turn the heating off overnight, just leave the hot water on.
And use a hot water bottle!

 

[cronkle]

Forgot to add: one way to save power is to turn the heating off overnight, just leave the hot water on.
And use a hot water bottle!

Leaving the hot water on isn't a bad idea. It's gas and not electric and the insulation of the boiler can't be perfect so some heat leakage is bound to occur. Just need to remember to leave the door to the locker that it's in open.

 

[Markd]

Having portable solar panel give you the opportunity to maximise your harvest by optimising its angle to the sun.
Whether it will provide enough energy to support regular overnight heating is debatable.
Adding a second battery will increase time before recharging by an alternative means.
Second duvets definitely a cheaper long term option

 

[in h]

Having portable solar panel give you the opportunity to maximise your harvest by optimising its angle to the sun.
Whether it will provide enough energy to support regular overnight heating is debatable.
Adding a second battery will increase time before recharging by an alternative means.
Second duvets definitely a cheaper long term option

Oh, I have a different opinion.
A fixed solar panel on the roof is a fit and forget fix. You can ignore it year after year. Yes, you can align a portable panel to face the sun and get more output, but it's far easier, and just as cheap, to fit twice as big a panel flat on the roof instead
You see people setting up their portable panels, then a few hours later the sun has moved and the panels are in shade. Or they blew over in the wind
And even if you don't mind the faff of setting up and packing away, they are always at risk of theft or damage.
For me, one of the best things about having a motorhome is that when you arrive, you just put the handbrake on and the ignition off. No setting up needed.

 

[Markd]

I too couldn't be bothered with the hassle but as cronkle has used one for years I thought I could at least be supportive rather than tell him he's doing it all wrong

 

[wildebus]

Yes, blown air heating is quite a load. Truma reckon an average of 1.4A for the Combi 6 but I suspect it's a bit less than that turned down overnight.

Diesel heaters are far worse: not only do they have a bigger, more power-hungry fan, but they also have a fuel pump and they draw about 12A on every startup (and sometimes on shutdown).

I'm not sure if "Far worse" is quite right? Compared to a Truma, there is a bigger start-up current and there is also an increased shutdown current, where I think the glowplug comes on and the fan accelerates to clean the combustion chamber, but apart from those times, the running current is fairly acceptable IMO.
This chart shows how much power my Diesel (actually Kerosene ) Heater uses on Starting, Running, and Shutting down. The line after that is the general power draw from the battery so that should be used as the baseline - (so remove around 4W/0.3A) from the values

Heater Running - Power by David, on Flickr

Obviously the running line section would be longer usually. I did this as a test to capture the data.

The steady load of the heater drags the battery voltage down.

This is the same time period as the Wattage above, but with the current and voltage views.

Heater Running - Volt & Amp by David, on Flickr
So Startup hits 9A draw, running is around 1.2A (taking the baseline into account) and Shutdown has a rise to around 7.5A.
The Voltage drop was around 0.04V for the time the heater was in running mode compared to not running, so not that significant really, but then an additional current draw of 1.2A is not much. Over an extended period you would see that drop in a similar way to a Starter Battery just sitting maintaining "stuff"

Typically a single 100Ah battery on a split charge relay or VSR will cope in a motorhome just running lights and water pump. Add a USB phone charger and you should be OK. A TV is OK if it isn't used much. Maybe.

It's when you add long term loads like a heater with fans, or a 12v-only fridge, or you add big loads like an inverter that the problems start.

1.4A average load from the heating doesn't sound much, but it's 33Ah per day. That's about the whole usable capacity of a 100Ah leisure battery running off a split charge or VSR system. You would need to drive for two or three hours each day to replenish it.

It really would have to be blooming cold to have the heater on 24/7 when in the van. The heater in the example above is a 2kW and I rarely have had the heater on for more than an hour or so to get up to temp (and I do like it pretty warm!). On a restart, because the heater is probably still pretty hot internally, the startup current is notably reduced as the glowplug does not stay on for so long and need less current to get upto temp.

2 to 3 hours to replenish a 33Ah discharge? It does depend on the battery bank capacity, but I would say if your heater had taken the kind of energy out of the battery where you were concerned (so maybe down to 60% say?), then you would get the great majority back quite a bit quicker than 2 hours from either a VSR or B2B.

 

[in h]

I too couldn't be bothered with the hassle but as cronkle has used one for years I thought I could at least be supportive rather than tell him he's doing it all wrong

If it works for him, he's not wrong.
Otherwise, he just has to stick it to the roof and he's sorted.

 

[wildebus]

Having portable solar panel give you the opportunity to maximise your harvest by optimising its angle to the sun.
Whether it will provide enough energy to support regular overnight heating is debatable.
Adding a second battery will increase time before recharging by an alternative means.
Second duvets definitely a cheaper long term option

second duvet? nah, I have an electric blanket in my van. And I have to tell you it works brilliantly!
I have it fitted between the main mattress and the mattress topper - so when it is working it is warming up the entire topper (bit like a giant hot water bottle). Turn it on while en-route to your destination, or in the afternoon while you are getting some solar and jobs a good 'un