Help understanding generator output & battery charge rate??

[Tony R]

I currently have a Ultra LX jetski which I use only for fishing and spearfishing out wide.

The workshop manual tells me that the maximum generator output is 16Amps at 14V......which would probably be at max 7000 RPM.

I have 2 x Yuasa YTX 18L-BS (18amp hour / 275CCA) batteries on board connected via a BEP (three position selector switch) and a BEP voltage sensing relay.

My goal is to replace the old batteries with 2 x new DEKA ETX 20L (AGM) batteries...(18AMP hour / 320CCA)

The battery specification data tells me that the -

Yuasa's need reg. charge rate of 1.8amp
Deka's need reg.charge rate of 4.0amp



My question is -

1. Does the generator/stator have the capacity to charge both DEKA batteries at the same time when the BEP unit switches them in parrellel?

My battery/batteries are always fully charged prior to heading out, so the output would only be topping up the battery. The only battery use is starting....which could take place 20 to 30 times a day when drift fishing etc...
The only electronics I have on board is a Lowrance HDS5 gen 2 which is used for most of the day and connected to the house battery.

Starting to get confusing........

[johncar]

The way I see it Tony, the first battery will charge until it is pretty much fully charged. It's internal resistance will get higher as it charges.
When the voltage sensitive relay senses this by measuring the voltage of battery 1 and when the first battery voltage is high enough it will parallel the second battery for charging only. Because the first batteries resistance is high it will draw very little power now from the alternator and if the second battery is partially discharged it will draw power until it too reaches full voltage.
When both are fully charged then neither of the batteries will draw much but topping up from whatever is drawing power at the time.
If the system is running properly you should never be fully charging both batteries at once. The VSR will prioritise back to the start battery any only send charge power to it alone until it is again up to the VSR's voltage theshold to parallel battery 2's charge circuit.

[NAGG]

for me the key is you are pumping in 16amps / hr - the draw on your sounder is ? ...... 5amps/hr maybe .
So I guess if you run a sounder for 2 hrs with a 20 amp house battery (with no motor) - then you have to run the motor for 35 mins or there abouts to get the charge back up .

chris

[peterbo3]

A quick look at the ski specs shows that it is an inline four cyl with fuel injection. The engine control unit & various sensors are going to chew some amps & the fuel pump will too if it is electric. Plus the instrument cluster will want some as well. You need to get a puter readout from the service guys showing actual amp output at various revs that is available to top up the batteries. Or put a clamp meter on the (+) battery cable. Until you get some hard info, it is just guesswork.

[Spiderpig]

The way I see it Tony, the first battery will charge until it is pretty much fully charged. It's internal resistance will get higher as it charges.
When the voltage sensitive relay senses this and the first battery voltage is high enough it will parallel the second battery. Because the first batteries resistance is high it will draw very little power from the alternator and if the second battery is partially discharged it will draw power until it too reaches full voltage.
Then neither of the batteries will draw much.
If the system is running properly you should never be charging both batteries at once. The VSR will prioritise.

Standard VSR's dont work like this.

If the VSR is wired between the two batteries it should work like this.

When the motor is not running, the voltage should be 12-12.8V, the VSR senses this and remains open separating the batteries and stopping both of them from going flat.

When the motor is running, the volts rise to roughly 13.8v, the VSR senses this and closes, charging both batteries.

I would only charge one battery at a time. It really depends how your selector switch is set up as to how you can make this work for you. It is possible to run your load off the selector swith and have no load connected directly to the batteries(always leaving a charged battery for starting). This negates the need for a VSR and will be manually switched.

[Bros]

Standard VSR's dont work like this.

If the VSR is wired between the two batteries it should work like this.

When the motor is not running, the voltage should be 12-12.8V, the VSR senses this and remains open separating the batteries and stopping both of them from going flat.

When the motor is running, the volts rise to roughly 13.8v, the VSR senses this and closes, charging both batteries.

Isn't that what he said?

The second last sentence is not quite right but is near enough.

[Tony R]

The way I see it Tony, the first battery will charge until it is pretty much fully charged. It's internal resistance will get higher as it charges.
When the voltage sensitive relay senses this and the first battery voltage is high enough it will parallel the second battery. Because the first batteries resistance is high it will draw very little power from the alternator and if the second battery is partially discharged it will draw power until it too reaches full voltage.
Then neither of the batteries will draw much.
If the system is running properly you should never be charging both batteries at once. The VSR will prioritise.

Thanks for info so far guys.

I guess johncar is right....only once the first battery is fully charged will the VSR switch over and parrellel both batteries ...generator should only then have to charge the second battery as the first is fully charged.

Seems simple....thanks again.......

Incidently the HDS 5 GEN 2 consumes 1amp per hour with backlight on......

[juggernaut]

My question is [*]Does the generator/stator have the capacity to charge both DEKA batteries at the same time when the BEP unit switches them in parrellel?..

If it doesn't have sufficient charge capacity the VSR in the BEP cluster it will chatter.....so I guess you'll soon know. To avoid the chatter ensure your second battery is within the BEP recommended amp hr rating.

Q: Why does my VSR ‘chatter’?
A: Because the charging system is too small for the batteries and
this is not allowing the VSR to work properly. Instead, once the
starting battery has reached the right voltage and the house battery
is connected the systems voltage is ‘caving down’ below 12.7 volts
and the relay is automatically disconnecting. The voltage then rises,
the relay re-engages; then the voltage drops the relay disengages
and the ‘chattering’ sound is heard as the relay quickly switches in
and out. Refer to battery sizing chart on next page.

More information can be found on our Website www.bepmarine.com.

[CATchin'Em]

hang on fellas. I am not saying anyone is wrong or critising anyone but read exactly what choc_E wrote and it is spot on to the letter for how a vsr works. ( It senses voltage hence voltage sensitive relay)

Also listern to peterbo he is also correct use a clamp meter and you can be certain it is ok.
I would think you would not have any problems as 8 amps is a lot to use but use a clamp meter and find out because every engine is different and you never know anymore

[johncar]

Sorry folks if my thoughts on this are misleading. I edited my post and hope it is clearer. My references are to the charge circuit only, not battery output. It's just a discussion isn't it?
It seems that the poster is just upgrading his batteries to slightly higher capacity. No additional or large power loads from what I read.
The new batteries may draw a couple of more amps if significantly discharged but not at once as there is a VSR in circuit.
So I think at most you will only draw about 2 more amps at worst.

[CATchin'Em]

yeah no maybe. REALLY??

[FishHunter]

I dont see how your Jetski can have a generator they went out of fashion about 40 years ago. Most things nowadays have Alternators maybe you should check as there is a big difference in the way they work.

[Fed]

I think you misunderstand how a vsr works. all it does is link the two batteries when engine is started.
when engine is started 13.8v+ is put down your wires therefore if you connect something to it it is getting 13.8v+.

If the current draw on the system is higher than the output capacity of the motor then the voltage will drop it's bundle. Not unusual to see low 12V numbers even though the motor is trying to deliver 15 volts but the battery is down a little.

[cormorant]

http://www.bepmarine.com/media/produ...7c846d96d1.pdf

http://www.bepmarine.com/media/produ...7c7b7be28f.pdf

There are several types of "VSR" that work in different ways . Above is one of BEP spec sheets.

They have a new digital model out late last year

http://www.bepmarine.com/product-mai...ing-relay-dvsr
http://www.bepmarine.com/media/produ...f332a1f818.jpg


Edit Added BEP new model.

[Tony R]

I dont see how your Jetski can have a generator they went out of fashion about 40 years ago. Most things nowadays have Alternators maybe you should check as there is a big difference in the way they work.

FishHunter....a jetski has a generator/stator much like a dirt bike.....

I'm assuming due to lack of space there is no alternator...remember an alternator is belt driven which would take up a large amount of space...etc....

Regardless...it seems my questions have been answered...the stator will only really be charging a single battery, not both batteries..once the first battery is charged to 13,7volts the VSR unit opens or closes ?? and starts charging the second battery...case closed.

Thanks for all the advise seems I have solved the issue......love this site!!!