Originally Posted by gpeacock
Both Stan Honey Here
And Entropy Here
describe different approaches on how to use the LVD/HVD contactors.
Entropy wants a disconnect to be independent of any failure (except maybe the contactor itself) and requires power to keep it closed.
Stan felt that that "powered closed" was too much of a power waste and trusts his BMS to send the signal to open the contactor.
Both have used basic circuitry to modify how the contactors interact with the BMS which you can find detailed in the links I've posted.
Toddedger: Your approach on the load side sounds great for a LVD. Does this mean your charging
sources are on a separate bus and your main master relay also acts as a HVD? If so how do you use your BMS to power the second contactor closed yet also let it work as a HVD?
Like NWN and exmaggiedrum I am having a hard time wrapping my head
around this part of the system without great expense (in $ or Ah).
The Blue Sea 7713 remote battery
switch I am (currently) planning to use has a manual override switch built in to it so it can be operated independent of the relay.
I may have a new issue after rereading Stan Honey's PDF. On the section on parasitic draws he says he used a BS 7712 switch. That is the previous version of the one I have ordered which is now the 7713. I think they are basically the same so they use the same relay (I would expect but don't know for sure). Anyway, he says that the BMS signal is (basically) the wrong kind. (I tried to cut and paste his paragraph but it was totally messed up here). He said he had to use a P-FET and resistor to convert the signal to a "12 volt pull-up control signal". I'll have to get someone to translate that for me and then decide if I need to do that. He says the HP BMS uses a "open collector" pull down output for solenoid control and that wouldn't work for his 7712.
I like the feature of the manual override on the 7713 which is why I wanted to use it, so there isn't a single
point of failure on the main battery
bus (like Entropy's system and as per the HP installation
On my (current) design I am putting both of my alternator
outputs to the Main Bus as opposed to putting them on the HVC bus. As per the discussion by Entropy I am going to take the risk of a problem from that since (a) the Main Switch will prevent overcharging just 0.005 volts higher, (b) I will have a alarm siren on reaching the warning level and can manually shut off the alternators, and (c) I am putting in two field disconnect relays for the alternators which will be driven by the HVC control from the BMS (one relay in front to change the "logic" so that the fields are closed circuit until a HVC warning event). See HP BMS manual and Entropy as to changing the "logic".
I will look into whether I have to use the P-FET and resistor to control my main bus "protection level" switch or whether is will work as per the BMS manual or whether I can use another solenoid relay to send the right signal to open it when the protection level is reached.
I hope all this complexity is really necessary and not just extra like Rich Boren says. It hasn't been a cheap