Buck Turgidson
Well-known member
As previously mentioned, when your house battery is big enough to take the starter load without flinching it will stay connected during engine starts .
Big house battery vs Cyrix VSR
- Thread starter Buck Turgidson
- Start date
PaulRainbow
Well-known member
Mostly works like that, without a problem, provided the wiring and fuse are suitably sized.
If it does cause a problem, wire a normally closed relay in series with the negative VSR wire and connect the coil trigger wire to the starter solenoid positive. As soon as you operate the starter the VSR disengages.
If it does cause a problem, wire a normally closed relay in series with the negative VSR wire and connect the coil trigger wire to the starter solenoid positive. As soon as you operate the starter the VSR disengages.
sailoppopotamus
Active member
So that is happening here exactly? Is the starter battery not dropping below the 12V required to have a swift disconnect? If so, is that because you've got a fantastic starter battery, or is it because charge flows from house to starter during cranking? Either way, is it really a problem?
Buck Turgidson
Well-known member
Too late for that. It hid a dead start battery which I only found by the sound of it sizzling after engine start as it boiled under alternator charge.
Buck Turgidson
Well-known member
The starter battery is doing nothing because the house battery is a monster and is doing all the work.
sailoppopotamus
Active member
It must be doing *something* though, as they are effectively in parallel. I just replaced my starter battery and installed a Cyrix and I'm pretty sure the engine fires up more easily now. I wonder if that could be due to the service battery participating. The cheapskates at Victron didn't include an LED indicator for the 120A Cyrix so you've got no idea what the switch is doing.
Buck Turgidson
Well-known member
The video shows my house doing most of the work. That’s with a new 60ah start battery. I don’t have an ammeter on the start batt so I can’t say for sure how much load it takes but the previous one was dead and the engine started normally with the same load on the house bat.
geem
Well-known member
We have large led voltmeter for our batteries on the main panel. They tell you quite a lot
Buck Turgidson
Well-known member
When the batteries are parallel due to the VSR being closed the voltage is the same for both.We have large led voltmeter for our batteries on the main panel. They tell you quite a lot
geem
Well-known member
Off course. But when it isn't closed, the engine battery voltage would drop if there was a cell down
PaulRainbow
Well-known member
If the engine battery is up to the job it will start the engine, the domestics will contribute some, but not do the whole job.
Buck Turgidson
Well-known member
Yes and that currently only happens at night when the engine is off.
Buck Turgidson
Well-known member
It’s the difference in capacity/cca that has me thinking the whole philosophy of small starter battery/ large house bat is pointless if you fit a VSR and have solar charging. What I have is a main battery that does everything during the day and a small battery that starts the engine at night.
I fitted this system myself 6 years ago and at the time believed it was the optimal solution and have recommended the cyrix on here many times but I’m beginning to think it’s not all it’s cracked up to be.
I may as well have two equal sized batteries with this setup.
sailoppopotamus
Active member
CCA considerations aside, a good reason for having a separate starter battery is that there's no way for the house loads to drain it and leave you stranded. Even in your case the Cyrix accomplishes that, since the it will open if one of the batteries drops and stays below 12.8V.
Buck Turgidson
Well-known member
See the other thread. A charge voltage from an mppt will keep the cyrix closed . Even if it’s only milliamperes worth of current. You can only see battery voltage when the contact is open and that will happen when your solar stops or perhaps when your alternator overheats .
I’m thinking worst case scenario’s because that’s what the system should be designed for.
I didn’t expect this standard system to mask a failed start battery but it did. Hence my reassessment.
sailoppopotamus
Active member
See I think this is what I don't get, my understanding is that if the battery is over 13V it must be charging, i.e. more current is going in than being consumed. I'm hardly an expert on the matter though.
Buck Turgidson
Well-known member
Battery discharging at 13.05v with charger connected in storage mode at 13.2 . Charger amps increased as load increased. This was a transmission on vhf. h ipower. Charger amps increased to about 2.5 at the same time so the battery can definitely discharge with voltage above 13v when charging source is paralleled.
lustyd
Well-known member
You have no way to measure the battery voltage, that’s the whole point. The internal resting battery voltage could be 5V for all you know, but the circuit voltage might be 13V and that’s what the VSR and your multimeter would measure. They are very dumb devices made out to be very clever devices.
lustyd
Well-known member
Thanks, I see this consistently and it helps explain my other thread. What many won’t realise is that although the shunt measures the discharge on the house bank, the start battery is also draining if the VSR is closed, it’s just not being measured
geem
Well-known member
No way. My smart shunt and mppt read the same. The MPPT uses the smart shunts voltage via Bluetooth. Even without, the MPPT voltage is only slightly different due to volt drop. I also have independent voltmeter on the main panel. They read the same battery voltage but independently
