B2B

[two]

B2B Battery-To-Battery chargers sometimes called DC-DC chargers, allow you to charge your leisure battery from your alternator whilst driving. ... They are capable of providing a full intelligent multi step re-charge of your leasure battery.

 

[JustmeCC]

How much are B2B battery chargers and who would fit them

 

[Tombola]

they range in price from £100+
you can diy fit, plenty of instructions online, and a fair few threads on here

Check you really need one first, by monitoring how much charge you current set up is throwing in already

 

[dash300]

How much are B2B battery chargers and who would fit them

This member is beatified on this site. Handy for me as in my back yard but does supply with comprehensive instructions or pop down for a trip with a day on his campsite.

Home - VanBitz

Van Bitz is the UK's leading motorhome security installation company with an envious reputation for providing first class services and cutting-edge security

www.vanbitz.com

 

[LithiumConvert]

I think it is worth saying that a B2B can be used used to charge any one battery from any other one, although they are most commonly used to charge a leisure battery from the starter battery - when the engine is running and the alternator is delivering power.

They are often deemed to be essential on vehicles fitted with a smart alternator - with the B2B activated by the D+ (engine running) signal from the alternator.

Most are capable of providing a full intelligent multi step charge of the connected battery and often have the option to select the battery type and charge rate.

Some will even provide output power when no battery is connected. Often used to run fridges or other equipment from the alternator when the engine is running.

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[Nirvanauk]

How would I know if my van had a smart alternator?

 

[Bobby-gg]

How would I know if my van had a smart alternator?

Ask it a really hard question!

Sorry, I'll get my coat...........

 

[LithiumConvert]

How would I know if my van had a smart alternator?

I am sure others will have a more technical answer, but my simple check is:-

Plug a voltmeter thingy into the engine cigar lighter socket. A smart alternator will give you the following vaues:-

12.x volts when you are driving (foot on accelerator)​

13.x volts on engine overrun​

14.x volts when breaking.​

If the voltage is substantially constant, then you do not have a smart alternator

 

[Lenny HB]

How would I know if my van had a smart alternator?

Negative terminal of the starter battery will have a shunt (small black box).

 

[nicholsong]

I am sure others will have a more technical answer, but my simple check is:-

Plug a voltmeter thingy into the engine cigar lighter socket. A smart alternator will give you the following vaues:-

12.x volts when you are driving (foot on accelerator)​

13.x volts on engine overrun​

14.x volts when breaking.​

If the voltage is substantially constant, then you do not have a smart alternator

So why does it behave like that? What is its motivation?

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[LithiumConvert]

So why does it behave like that? What is its motivation?

The answer to that is far too complicated (and, perhaps, too controversial) for this part of the forum.
(and I would suggest, particuarly, this B2B thread)

Search "smart alternators" for full information.

 

[fred_jb]

I don't think it is that complicated really.

Smart alternators reduce their voltage and hence the amount of charging they provide during normal running. This reduces the alternator load on the engine and as a result slightly improves fuel efficiency.

These alternators, in conjunction with ECU programming, try to mainly provide higher voltages and hence charging when the throttle is closed and when braking. This means the energy provided to the battery is free in that it is produced via recovering energy from the momentum of the vehicle and not through burning extra diesel.

 

[fred_jb]

I would add that B2B type devices aim to defeat the fuel saving characteristics of smart alternators by making it possible to extract large charging currents from the alternator even when the voltage output of the alternator is too low to do so naturally.

They do this by electronically converting the low voltage produced in fuel saving mode to a higher voltage which will then allow large amounts of current to flow into the attached leisure battery during normal running and not just when decelerating and braking.

This effectively subverts the fuel saving regime which the vehicle has been designed to provide, so is not necessarily a good thing to do if you can sufficiently charge the leisure battery by other means such as solar panels or mains charging via an EHU. Some people including myself have fitted a switch the the D+ input to the B2B so as to be able to disable it when not required.

 

[Pausim]

I would add that B2B type devices aim to defeat the fuel saving characteristics of smart alternators by making it possible to extract large charging currents from the alternator even when the voltage output of the alternator is too low to do so naturally.

They do this by electronically converting the low voltage produced in fuel saving mode to a higher voltage which will then allow large amounts of current to flow into the attached leisure battery during normal running and not just when decelerating and braking.

This effectively subverts the fuel saving regime which the vehicle has been designed to provide, so is not necessarily a good thing to do if you can sufficiently charge the leisure battery by other means such as solar panels or mains charging via an EHU. Some people including myself have fitted a switch the the D+ input to the B2B so as to be able to disable it when not required.

I prefer to think of the B2B as a device that enables the proper charging of a leisure battery. Yes the alternator has to work harder whilst doing this and higher output alternators are fitted for this purpose. There is of course a fuel cost to charging a leisure battery but when it is full the better B2Bs will automatically shut down without the need for switching off the D+ connection. At this point the fuel savings of the smart alternator will be back in play.

 

[fred_jb]

I guess it is a matter of balancing the extra fuel cost of alternator charging, which will be fairly minimal and maybe some extra wear and tear on the alternator and it's drive belt, versus the "free" energy available from solar or from the mains if you will be on an EHU anyway for other reasons. Having a D+ switch gives you the choice.

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[Pausim]

I guess it is a matter of balancing the extra fuel cost of alternator charging, which will be fairly minimal and maybe some extra wear and tear on the alternator and it's drive belt, versus the "free" energy available from solar or from the mains if you will be on an EHU anyway for other reasons.

The B2B also protects the alternator and wiring from heavily discharged batteries demanding too many Amps.

 

[fred_jb]

The B2B also protects the alternator and wiring from heavily discharged batteries demanding too many Amps.

Yes good point, far preferable to the old split charge relay systems which effectively just connect the leisure battery directly to the alternator.