Battery sums please

[simonfraser]

So if you are not using the start assist facility it wont close in the way you seem to think due to the starter battery voltage falling below the house battery voltage. It will only close after the engine has started and the starter battery volts have risen above 13.

i

ok, well that is v odd, why does the fuse blow then ?

or does the cyrix latch due to the shore charger and when i disconnect the charger before i start the KAD it stays latched for a while ?

 

[lw395]

ok, well that is v odd, why does the fuse blow then ?

faulty cyrix ?

Is your first post correct or not?

 

[pvb]

ok, well that is v odd, why does the fuse blow then ?

faulty cyrix ?

The fuse blows because it isn't big enough. This was all covered in your previous thread "VSR blowing fuses". Why keep asking questions if you ignore the advice you're given?

If the Cyrix manual tells you to fit a 120A fuse, why have you got a 35A fuse?

 

[VicS]

ok, well that is v odd, why does the fuse blow then ?

faulty cyrix ?

At what point in the starting sequence does it blow. If it blows as soon as you crank the engine then it suggests that the VSR is indeed closed ....... in start assist mode ? or faulty

If it blows after the engine has started it is doing so because the charge current passing through it is greater than your fuse value ....... you keep referring to a 35 amp fuse but I am sure you where advised ages ago that 35 amps is not enough.

Are you sure the 120 amp Cyrix is the correct size for your installation ..... it is the smallest. There is a 230 amp version and a 400 amp model. I feel sure that one of the larger ones is necessary if you use start assist for an engine as large as a KAD 44

What happens if you put the recommended 120 amp fuse in the circuit?

 

[lw395]

....

What happens if you put the recommended 120 amp fuse in the circuit?

I expect it will blow at much greater expense?

 

[halcyon]

ok, well that is v odd, why does the fuse blow then ?

or does the cyrix latch due to the shore charger and when i disconnect the charger before i start the KAD it stays latched for a while ?

I think they have a odd low cut in voltage, plus a closed for a fixed time period, that I totally disagree with, resulting in a closed VSR when the engine is started, thus power is drawn from both batteries, hence blown fuse.

If you are using link start with very bad engine battery, the engine battery should be isolated and service battery only used, once up and running the isolator and VSR will charge the engine battery. A 1.7KW motor could be up to 500 / 600 amp stall ( motor output, not input ) 200 / 250 amp cold engine, fuse ? rating ?

Brian

 

[VicS]

I expect it will blow at much greater expense?

That would confirm that the VSR is closed when we are not expecting it to be closed.

If it doesn't though it simply underlines the advice previously given to fit a larger fuse than 35 amps.

Some progress which ever way you look at it.

 

[simonfraser]

bigger fuse is on the way

but, that does not explain why it blows in the first place as it should not be latched
reading the manual again of the cyrix,

the shore power is disconnected b4 i start the engine, according to the cyrix manual it may stay connected for 10 mins at a battery voltage of 13V

so if i disconnect the shore charger and then launch the boat, that can be within the 10 mins window, so the cyrix is latched and pop goes the fuse when i start the KAD ?

 

[lw395]

That would confirm that the VSR is closed when we are not expecting it to be closed.

If it doesn't though it simply underlines the advice previously given to fit a larger fuse than 35 amps.

Some progress which ever way you look at it.

I would be expecting the VSR to be closed, because the first post in this thread states that the starting point is
"one 12V red top battery and one 12V Trojan 105 Ah, both fully charged, both floating at 13.5"

The Cyrix VSR remains closed until the voltage drops below 12.8V, when it will open after a 3 minute delay, or progressively shorter delays if the voltage drops lower.

This thread exemplifies why I'm not as enthusiastic about VSRs as PaulRainbow. VSRs seem to lead some people into problems.

Presumably there is either a float charger (or solar) still in place, or has just been disconnected and the batteries have not fallen to a resting voltage of say 12.7V, and the VSR allowed to open in due course.

Starting with the VSR closed as a default option almosts negates the value of having a separate engine battery.

 

[simonfraser]

excellent, now we / i understand the issue.
yep, solar panel on the roof, so the VSR is hardly ever going to open which did not help in spotting the cause

'Starting with the VSR closed as a default option almost negates the value of having a separate engine battery'

so how would i go about getting both batteries charged from the alternator and solar ?
leave the VSR and the low fuse, but take it out / switch it off for starting ?

 

[lw395]

bigger fuse is on the way

but, that does not explain why it blows in the first place as it should not be latched
reading the manual again of the cyrix,

the shore power is disconnected b4 i start the engine, according to the cyrix manual it may stay connected for 10 mins at a battery voltage of 13V

so if i disconnect the shore charger and then launch the boat, that can be within the 10 mins window, so the cyrix is latched and pop goes the fuse when i start the KAD ?

Bingo..
If you run some minor load for a short period, it might bring the voltage down to open the VSR quicker? A few lights? engine room fan? This weather, glowplugs on the diesel?

The problem is, if the VSR is closed, there is no reason to assume the majority of the starting current won't come from the house bank, particularly as the engine battery gets old.
So the fuse, VSR and all wiring need to be good for that. Or high enough resistance to limit the current, which is unlikely to be the case.

 

[PaulRainbow]

The VSR will be closed if the mains charger has just been turned off and the Trojans are floating at 13.5V, however, if the starter pulls the Trojan voltage down the VSR could disconnect in 1 sec.

There are two Trojans, not one.

The VSR is suitably rated for it's job. It is there to provide split charging, not constant jump starting for a 3.6 litre 260HP engine. The 120a rating is well over spec for the charging systems fitted.

The VSR is rated at 120a, but this would require 20mm cabling, which i think is ridiculous on 6mm studs and is unnecessary if the system is correctly setup.

The Red Top battery is connected to a 6cyl 3.6litre 260 hp engine and a windlass, the battery is totally unsuited for purpose and was fitted against my explicit advice not to do so. My advice was to fit a starter battery suitable for the engine in use. I have, several times, told Simon this and he steadfastly refuses to accept my advice.

Fitting ever bigger fuses to overcome the shortcomings of the battery is not the answer, the engine battery should be fit for purpose. The VSR was not designed to be regularly subjected to surge loads of a hefty engine starting and a windlass, both fitted to an inadequate battery.

The Red Top should be replaced with a suitable battery or the VSR should be replaced with a low loss splitter. Anything else will be a bodge and lead to further problems.

 

[PaulRainbow]

I would be expecting the VSR to be closed, because the first post in this thread states that the starting point is
"one 12V red top battery and one 12V Trojan 105 Ah, both fully charged, both floating at 13.5"

Exactly. Although the boat has two Trojans (makes no difference to your point though)

The Cyrix VSR remains closed until the voltage drops below 12.8V, when it will open after a 3 minute delay, or progressively shorter delays if the voltage drops lower.

Unless there is a big drop, in which case it opens in 1 sec, that doesn't seem to be the case though.

This thread exemplifies why I'm not as enthusiastic about VSRs as PaulRainbow. VSRs seem to lead some people into problems.

The problem isn't being caused by the VSR, it's the incorrect battery.

Presumably there is either a float charger (or solar) still in place, or has just been disconnected and the batteries have not fallen to a resting voltage of say 12.7V, and the VSR allowed to open in due course.

A Sterling 30a mains charger and some solar power. The VSR will therefore be closed. Nothing wrong with that though, if the rest of the system is in spec. I have 260w of solar and a 30a mains charger, my engine battery is a large, heavy duty starter battery and my windlass is also connected to it. My VSR is probably closed most of the time, due to one of the chargers being on. I have never, ever, had a VSR fuse blow on my boat, or on any other boat that i have fitted a VSR to.

Starting with the VSR closed as a default option almosts negates the value of having a separate engine battery.

I don't think so. A properly spec'd engine battery will start the engine without pull a huge current through the VSR.

 

[halcyon]

I don't think so. A properly spec'd engine battery will start the engine without pull a huge current through the VSR.

The problem the OP has is the extended lock in period that the VSR has, the weather is cold so increased loading on starter motor, batteries are cold. So initial loading is higher, period is longer, battery specs could well be different due to weather, come warmer weather all may well work okay again.


Brian

 

[simonfraser]

Bingo..
If you run some minor load for a short period, it might bring the voltage down to open the VSR quicker? A few lights? engine room fan? This weather, glowplugs on the diesel?

The problem is, if the VSR is closed, there is no reason to assume the majority of the starting current won't come from the house bank, particularly as the engine battery gets old.
So the fuse, VSR and all wiring need to be good for that. Or high enough resistance to limit the current, which is unlikely to be the case.

tnx

 

[PaulRainbow]

The problem the OP has is the extended lock in period that the VSR has, the weather is cold so increased loading on starter motor, batteries are cold. So initial loading is higher, period is longer, battery specs could well be different due to weather, come warmer weather all may well work okay again.


Brian

No, he has solar panels, so the VSR will mostly be closed anyway. The problem is the battery is not suitable, therefore it tries to pull high current through the VSR.

The battery is new, it just isn't the right one for the engine.

 

[halcyon]

No, he has solar panels, so the VSR will mostly be closed anyway. The problem is the battery is not suitable, therefore it tries to pull high current through the VSR.

The battery is new, it just isn't the right one for the engine.

What battery are you recommending that will not pull current from a battery parallel with it during starting?

Brian

 

[simonfraser]

No, he has solar panels, so the VSR will mostly be closed anyway. The problem is the battery is not suitable, therefore it tries to pull high current through the VSR.

The battery is new, it just isn't the right one for the engine.

so if i have solar panels that close the VSR, why do i need a VSR ?

 

[VicS]

so if i have solar panels that close the VSR, why do i need a VSR ?

The main purpose is to charge the house battery bank from the engine alternator without it being permanently connected to the starter battery. A single sensing VSR, which would probably be better for you than the dual sensing one you have at present, will allow that to happen as soon as the engine start battery volts rises to the cut in volts. It will cut out again shortly after the engine is stopped.

The single sensing VSR would not be turned on by the solar panel charging the house battery like your dual sensing one is.

An emergency start paralleling switch, which I believe you said you have, will still allow emergency use of the house battery independently of the VSR.

 

[simonfraser]

The main purpose is to charge the house battery bank from the engine alternator without it being permanently connected to the starter battery. A single sensing VSR, which would probably be better for you than the dual sensing one you have at present, will allow that to happen as soon as the engine start battery volts rises to the cut in volts. It will cut out again shortly after the engine is stopped.

The single sensing VSR would not be turned on by the solar panel charging the house battery like your dual sensing one is.

An emergency start paralleling switch, which I believe you said you have, will still allow emergency use of the house battery independently of the VSR.

Tnx, did not know those existed, would have been good to know.