Charging starting battery from solar?

[Akestor]

Another option- why not just turn the 1-2 both switch to both to give some juice to the starting battery from the solar? Actually to do manually what a VSR would do.( is there a technical error in that? except forgetting it and draining the start battery with house loads)

 

[Stemar]

except forgetting it and draining the start battery with house loads)

As we get older, such issues become more likely.

 

[vyv_cox]

As we get older, such issues become more likely.

Just as likely when I was younger. I never use 'both' for that reason but, as said earlier, I have a twin bank solar controller

 

[PaulRainbow]

Another option- why not just turn the 1-2 both switch to both to give some juice to the starting battery from the solar? Actually to do manually what a VSR would do.( is there a technical error in that? except forgetting it and draining the start battery with house loads)

Answeredyour own question

 

[Akestor]

Answeredyour own question

I was just wondering if there could be any issue at the moment of turning the switch to Both. Like if the house bank is at 13.8v and starting battery at 12.6v a momentary current surge damage any of the batteries or the switch. But on the other hand, same surge could happen in the VSR I suppose

 

[PaulRainbow]

I was just wondering if there could be any issue at the moment of turning the switch to Both. Like if the house bank is at 13.8v and starting battery at 12.6v a momentary current surge damage any of the batteries or the switch. But on the other hand, same surge could happen in the VSR I suppose

Never seen this happen, but leaving on and draining all betteries, seen that a few times.

 

[[70521]]

I was just wondering if there could be any issue at the moment of turning the switch to Both. Like if the house bank is at 13.8v and starting battery at 12.6v a momentary current surge damage any of the batteries or the switch. But on the other hand, same surge could happen in the VSR I suppose

What do you think happens when you turn on your engine or shore power?

 

[Akestor]

What do you think happens when you turn on your engine or shore power?

hmmm good question. In the case of shore power I guess the charger will give its max output if needed? I have observed my 50amp alternator giving 30 amps to the 200AH house bank and quickly dropping. ( battery switch to position
2)
But in the case of the house bank, they are carbon lead deep cycle and they may send some big current to the 50 amp starting battery when switch turned to both ( without the engine running)
I may give it a try, and let you know if I fry anything lol

 

[Stemar]

Genuine question - what sort of current would you get through a VSR or an 0-1-2-B switch when it connects a fully charged starter battery - say 800 cca - to a half discharged domestic bank of maybe 300AH?

In my musings about fitting one, I've worked on something like the maximum output of the alternator, but I'm wondering if it could be a good bit more?

 

[Akestor]

Genuine question - what sort of current would you get through a VSR or an 0-1-2-B switch when it connects a fully charged starter battery - say 800 cca - to a half discharged domestic bank of maybe 300AH?

In my musings about fitting one, I've worked on something like the maximum output of the alternator, but I'm wondering if it could be a good bit more?

Probably the max of the alternator plus plenty of amps from the starting battery moving to the domestic. My battery’s data sheet mentions a 50A max charge current (100Ah battery)

 

[PaulRainbow]

Genuine question - what sort of current would you get through a VSR or an 0-1-2-B switch when it connects a fully charged starter battery - say 800 cca - to a half discharged domestic bank of maybe 300AH?

In my musings about fitting one, I've worked on something like the maximum output of the alternator, but I'm wondering if it could be a good bit more?

Probably the max of the alternator plus plenty of amps from the starting battery moving to the domestic. My battery’s data sheet mentions a 50A max charge current (100Ah battery)

What happens when you connect jump leads from a fully charged battery, with a high output alternator running, to a car with a flat battery ?

Same as on a boat, nothing dramatic, current between the two batteries will be limited to the charge accaptance rate of the discharged battery, which will depends on the SOC and the cabling resistance.

I've fitted a lot of Victron 12A VSRs, the only way the current can pass though them in the scenario above is by using the "Start Assist" feature, which i never connect, but if it was connected, any more than 120A would blow the fuse. A more common scenario might be a flat (faulty) engine battery with a domestic bank that's fully charged and connected to solar, so the VSR is closed, hit the starter button and if the current is too high the fuse obviously blows.

I normally fit emergency parallel switches (same as switching a 1-2-B switch to "both", never had an issue using one with either a flat engine battery or domestic bank.

If the discharged battery/s are lead acid, i doubt the current would be more than 50-60A, if that.

 

[Refueler]

What happens when you connect jump leads from a fully charged battery, with a high output alternator running, to a car with a flat battery ?

Usually whatever clip is connected last SPARKS ..... that indicates more than just a few amps.

 

[PaulRainbow]

Usually whatever clip is connected last SPARKS ..... that indicates more than just a few amps.

It just indicates some current is flowing, doesn't have to be lots.

 

[Refueler]

It just indicates some current is flowing, doesn't have to be lots.

Friend of mine had his wedding ring catch when clipping on ... blew the ring apart and his finger permanently scarred.

On the matter of amps when cranking ... I'm old enough to remember days of bridging solenoid relay to start cars / trucks etc. One tool box I had - a screwdriver in it had half the shaft blown away by numerous use as that bridging tool.
People think that only 240v is dangerous ... 12v can kill as well !

 

[PaulRainbow]

Friend of mine had his wedding ring catch when clipping on ... blew the ring apart and his finger permanently scarred.

On the matter of amps when cranking ... I'm old enough to remember days of bridging solenoid relay to start cars / trucks etc.

You wish

One tool box I had - a screwdriver in it had half the shaft blown away by numerous use as that bridging tool.
People think that only 240v is dangerous ... 12v can kill as well !

In an emergency i used to use a 50p coin, it it didn't start smartly it got very hot.

 

[noelex]

12V itself will not kill you unless you bypass the high resistance of the skin, but you could certainly sustain a nasty burn or be killed indirectly through a fire or an exploding battery, etc.

Removing jewellery, watches and wearing eye protection is worth considering when poking around marine electronics, although I have never had any injuries from 12 V or 24V so the risk is not high.

 

[PaulRainbow]

Friend of mine had his wedding ring catch when clipping on ... blew the ring apart and his finger permanently scarred.

I'm finding it hard to believe that just connecting jump leads to a car will carry enough amps to blow a wedding ring apart.

 

[Refueler]

I'm finding it hard to believe that just connecting jump leads to a car will carry enough amps to blow a wedding ring apart.

I was there when it happened ... you can believe or not - not my problem.

 

[PaulRainbow]

I was there when it happened ... you can believe or not - not my problem.

He must have shorted it, you can't get enough current from a charged battery to a discharged battery to cause a gold ring to explode.

 

[noelex]

The typical cross-sectional area of many gold rings is not high. If you manage to create a short circuit via a gold ring it may melt. A copper wire with a similar resistance would behave in the same way.

Wearing a gold ring when it melts is not likely to be a good day .