VanBitz BM (again) (1 Viewer)

Nov 14, 2020
325
201
S.Yorks
Funster No
77,809
MH
Adria Compact SP
Exp
20 yr
.
Hi Folks

I'm still experimenting with small PV panels in van to keep Batts from deteriorating too much.

Reading through the BM helpsheet, I noticed that BM needs a 0.8v difference between Hab Batt and Cab Batt before it activates.

Does that mean that if Hab Batt is less than 13v, then Cab Batt will drop almost to 12v before anythiong happens ?
What if Hab Batt spends a lot of it's time around the 12.5 - 12.7v level ?

Can anyone explain the advantage of that, or am I getting it wrong (again) ?

cheers !
_
 

Emmit

LIFE MEMBER
Aug 14, 2009
8,114
17,946
Cornwall
Funster No
7,967
MH
Pilote Explorateur
Exp
Jan.2014
I'll hold myself up to ridicule.

I think it assumes??? that you have solar on the roof which, when in operation, whacks your hab. batteries up to 13v and above and transfers some of that to your van battery.
 

Kannon Fodda

LIFE MEMBER
Feb 26, 2019
2,666
8,202
Seek and Ye May Find
Funster No
58,768
MH
Autotrail V-line 540
Exp
I Make Schoolboy Errors!
If your hab battery is lead acid or similar so it's resting fully charged voltage is 12.6-7 then the VB Battery Master wouldn't trickle charge until the cab battery is getting below a 50% charge. But that could still be enough to keep you out of trouble if something had been draining your cab. The point being that the BM is really a background trickle top up to stop the cab becoming flattened from alarm systems and other things.

If you had solar, then when the hab is getting a solar charge the overall voltage would be higher and that differential will also kick in on the BM, so during the day you might see a trickle to the cab if it were at say 12.5V.

For those of us with lithium hab, our charged resting voltages can be well above 13.0V so the BM is always able to trickle charge as the cab starts to drop.
 

funflair

LIFE MEMBER
Dec 11, 2013
19,552
31,235
Guisborough
Funster No
29,351
MH
MORELO palace
Exp
since 2012
.
Hi Folks

I'm still experimenting with small PV panels in van to keep Batts from deteriorating too much.

Reading through the BM helpsheet, I noticed that BM needs a 0.8v difference between Hab Batt and Cab Batt before it activates.

Does that mean that if Hab Batt is less than 13v, then Cab Batt will drop almost to 12v before anythiong happens ?
What if Hab Batt spends a lot of it's time around the 12.5 - 12.7v level ?

Can anyone explain the advantage of that, or am I getting it wrong (again) ?

cheers !
_
I think that you basically have it right (y) I thought that the voltage difference was more like 0.65v and VB web site says closer to 0.5v as shown below, yes ideally there would be some external charge to the habitation battery to bring the voltage up a little bit, I used a BM for a good few years with Gel batteries to starter battery (no solar as it was under cover) and it worked fine, we now have a BM between LiFePO4 and starter battery and again it is fine but the Lithium does tend to sit that bit higher than a lead acid would, the starter is sitting around 12.6v.

Question: Will it work without a mains hook-up?
Answer: Yes. It is designed so that when the engine battery drops half a volt below the leisure battery, Battery Master automatically adjusts the charge and tops up the engine battery.
 
May 14, 2021
1,760
2,826
East Yorkshire, UK
Funster No
81,218
MH
ADRIA Twin 640SLB
Exp
Since 2012
My understanding too is that it works even when there is no charge to the hab battery, e.g. no solar or no sun out, inside etc whereas the similar Voltronic one will only work if there is a charge to activate it. I haven’t got one but am considering it if my solar doesn’t work well in winter.

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