Is a B2B charger necessary?

in h

Full Member

Messages
297
So the question is, what is the advantage or not of B2B over this VSR setup (see picture) that I found on
A b2b will charge both sets of batteries separately, allowing for their different capacity, different state of charge, different type.

A VSR joins them together whenever the voltage rises enough to suggest that there is some charging going on.

B2B is far better and will get the best from your batteries, both in terms of capacity and in longevity. Costs £100 to £500.

A VSR is cheaper. Usually about £20 to £30.

A SCR is far cheaper again, and works slightly better than a VSR, but needs one more (thin) wire connection. Costs 99p to £10.

Your choice. There's no right or wrong answer.
 

Dads Train

Full Member

Messages
6
A SCR is far cheaper again, and works slightly better than a VSR, but needs one more (thin) wire connection. Costs 99p to £10.

Your choice. There's no right or wrong answer.
SCR? sorry but dont know what this is?
 

in h

Full Member

Messages
297
SCR? sorry but dont know what this is?
Split Charge Relay. Basically, it is a 12v relay that connects the two positive terminals of the battery systems together. Its coil is powered from the ignition feed, earthed by the ignition light connection on the alternator. So it switches on when the alternator cuts in.

A VSR does the same thing, but is triggered by a rise in voltage (so a solar charger can switch it) but they normally use a diode and so lose about 0.6v. Doesn't sound a lot, but it makes quite a difference!
 

mistericeman

Full Member

Messages
205
Split Charge Relay. Basically, it is a 12v relay that connects the two positive terminals of the battery systems together. Its coil is powered from the ignition feed, earthed by the ignition light connection on the alternator. So it switches on when the alternator cuts in.

A VSR does the same thing, but is triggered by a rise in voltage (so a solar charger can switch it) but they normally use a diode and so lose about 0.6v. Doesn't sound a lot, but it makes quite a difference!
After 5 years or so of using a Durite VSR and punishing the 3 x 100ah leisure batteries
I can honestly say I've never missed that 0.6v.....

In real everyday use I suspect it makes little difference.
I've gone B2B on the Moho simply for the reason of combining solar mppt controller with alternator charging in one unit.
 

wildebus

Full Member

Messages
2,538
After 5 years or so of using a Durite VSR and punishing the 3 x 100ah leisure batteries
I can honestly say I've never missed that 0.6v.....

In real everyday use I suspect it makes little difference.
I've gone B2B on the Moho simply for the reason of combining solar mppt controller with alternator charging in one unit.
I don't think you would see a 0.6V drop TBH.

Screenshot of my setup with the solar connected to the Leisure Battery, and so also charging the Starter via the Victron Cyrix ...
1589221946724.png
Drop of 0.01V ...
 

familywagen

Free Member

Messages
9
Some people cast shade on the CTEK as an MPPT but I have 300 Watt of solar, with the CTEK and smartpass, 214ah battery and never had issues with flat batteries or running out of power, we do have an EHU but don't really need/use it apart from in the winter on a campsite we use it for the heating to save on gas
 

Dads Train

Full Member

Messages
6
Split Charge Relay. Basically, it is a 12v relay that connects the two positive terminals of the battery systems together. Its coil is powered from the ignition feed, earthed by the ignition light connection on the alternator. So it switches on when the alternator cuts in.

A VSR does the same thing, but is triggered by a rise in voltage (so a solar charger can switch it) but they normally use a diode and so lose about 0.6v. Doesn't sound a lot, but it makes quite a difference!
thank you.
the example I posted is essentially a vsr system but I was to activate the primary relay from the D+ rather than just any ingntion live. So would this then be close to a split charge system?
 

Markd

Full Member

Messages
696
thank you.
the example I posted is essentially a vsr system but I was to activate the primary relay from the D+ rather than just any ingntion live. So would this then be close to a split charge system?
Much better to use D+ rather than ignition live switching as the latter will connect in leisure to supply starter motor or may result in rush of current away from starter battery if leisure batteries are low.
 

in h

Full Member

Messages
297
I don't think you would see a 0.6V drop TBH.

Screenshot of my setup with the solar connected to the Leisure Battery, and so also charging the Starter via the Victron Cyrix ...
View attachment 54427
Drop of 0.01V ...
There is a semiconductor switch in line of a VSR. They all have a back voltage, none as low as 0.01v.
 

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