Yet another battery thread

[someguy]

Dirt bikes a 10 amp battery will start,500 to 600 amps to start a bus is a lot of difference there.anyways it's a mute point I got my answer from a LifePo4 manufacture

Max current is relative to the size of the battery.    Dirt bike batteries are as small and light as possible.  20Ah IIRC.

[windtrader]

As to why an RV with LiFePo4 batteries may label to not use as start batteries lies solely on two factors. Voltage needs to be the same. A 48v lithium battery pack starting a 24v or 12v start system is not recommended.


The only other factor is start amperage and that is directly related to battery capacity and C rating. Multiply the battery voltage by the nominal current (amp) rating of the battery and multiply by the discharge C rating (short duration, not continuous) and you get total watts available.


For example, my battery pack has 480 aH and 2C discharge for short periods is fine. This is 960 starting amps at 24v. The battery pack and cells need to be C rated as the connectors also need to be able to handle the current.

[luvrbus]

As to why an RV with LiFePo4 batteries may label to not use as start batteries lies solely on two factors. Voltage needs to be the same. A 48v lithium battery pack starting a 24v or 12v start system is not recommended.


The only other factor is start amperage and that is directly related to battery capacity and C rating. Multiply the battery voltage by the nominal current (amp) rating of the battery and multiply by the discharge C rating (short duration, not continuous) and you get total watts available.


For example, my battery pack has 480 aH and 2C discharge for short periods is fine. This is 960 starting amps at 24v. The battery pack and cells need to be C rated as the connectors also need to be able to handle the current.

Not quite the way James a engineer at Life Line explain it to me,jumping a 12 or 24 volt starting system with a 48v battery is funny, come on no one is that stupid I hope>I didn't ask about the jumping decal I read to mean jumping the house battery. I'll ask him about that.
You know the Delco 42 starter on your bus is a 900 amp 10 hp motor and they will draw those amps on a cold day I have seen higher, that is why lead batteries have cold cranking amps to turn that baby,The part I don't get is drawing a 100 amps from a 100 amp battery you only get maybe 30 seconds then drawing the same amps from a 100 amp battery would be like shorting one out I guess 

[chessie4905]

a major concern to me is, are these battery designs in the round screen color tv period or in the declining price vs screen size slide, seems like back when 8 track tapes were king. Good discussion though.
Also "theory" on what will be used on a planned system vs. actual money dropped for it needs to be considered.

[luvrbus]

a major concern to me is, are these battery designs in the round screen color tv period or in the declining price vs screen size slide, seems like back when 8 track tapes were king. Good discussion though.
Also "theory" on what will be used on a planned system vs. actual money dropped for it needs to be considered.

The part that throws me with LifePo4 is they last so long under normal use,then if you try  say you draw 500 amps from a 500 amp system for a starter they only last a few seconds as you well know sometimes a DD needs more than a few seconds .Then the high voltage a LifePo4 retains on a electronic engine it can cause damage to sensitive electronics I was told.I ordered 2 of the 100 amp LifeLines for Sonjas van I am going to give it try but I am keeping the 12v lead battery for starting.My price from LifeLine was no where near the $1000.00 for a battery there must be 1 hella of a markup on the LifePo4, lol freight prices are stupid high now on anything  80$ from CA to AZ is silly for 2 batteries     

[chessie4905]

Cliff, in your Prius, could be cheaper to drive there to pick up.lol

I don't  know how they are shipped, but UPS rates have gone up significantly here.

[Jim Blackwood]

Well I know we never had any problems starting a 6v tractor with a 12v battery and there are a great number of 6v vehicles running 12v without ever changing the starter. The starter runs faster which makes the engine start easier... unless it has a magneto and spins too fast for the impulse mechanism. But the starters don't burn up and the batteries don't explode.

We also never had a problem running a 12v starter on 24v. That's pretty much the same situation, so why would you expect to have a problem running a 24v starter on 48v? I don't see any difference there except the batteries. Are you guys saying that the lithium batteries can't handle the high starting current?

Jim

[luvrbus]

You hit a 12 or 24 starter with 48 v they will burn the armature and sling the lead I have done before with a 200 amp DC Lincoln welding machine trying to start a engine when I blew the battery up doing the same thing that was long,long ago

[Jim Blackwood]

Well that's just hilarious! You do realize that DC welder puts out something like 50 volts right? So at 200 amps you were putting some serious power into that battery, something like a full 10 Kw. I'd say it's no surprise it got hot.

And if you tried 48 volts on a 6v starter, well it'd run very fast for a very short time. But any decent starter will handle twice it's rated voltage for a reasonable time period and have a respectably long lifespan. It's done all the time. Like I said before. 12v on a 6v starter has been common since the 60's. 24v on a 12v starter isn't as common but is regularly done without issues. Why would 48v on a 24v starter be any different? The electrical loading is identical.

Jim

[luvrbus]

Well that's just hilarious! You do realize that DC welder puts out something like 50 volts right? So at 200 amps you were putting some serious power into that battery, something like a full 10 Kw. I'd say it's no surprise it got hot.

And if you tried 48 volts on a 6v starter, well it'd run very fast for a very short time. But any decent starter will handle twice it's rated voltage for a reasonable time period and have a respectably long lifespan. It's done all the time. Like I said before. 12v on a 6v starter has been common since the 60's. 24v on a 12v starter isn't as common but is regularly done without issues. Why would 48v on a 24v starter be any different? The electrical loading is identical.

Jim

I doubt I was getting 48 v since the Lincoln has adjustments for different voltage and amps and was no where close to max they have a DC plug for a grinder and other DC tools with 115 volt plug end and charging batteries with a DC welder is done all the time ,makes no difference starters built now blow a link if they sense voltage hi or lo hook 36 volts up to the starter on the series 60 of yours and give it a spin

[windtrader]

Clifford,


Have your contact explain C ratings, particularly discharge rating. If a battery pack is rated at 100 amps, then that is 1C and virtually all batteries can draw 100amps continuously. The battery is capable of discharging at more than 1C but that depends on two things: how much current can it draw and for how long. Each battery has a curve where it shows how long it can draw at various currents. Some batteries packs such as those Lipo used in RC planes can discharge at 30C but for not very long. So a 100 amp battery can discharge at 3000 amps for some time. But you have to have the wiring and other components rated to pass that much current too. So the whole system has to be designed and built to the spec it will be operating.


There is a lot to the details of advanced battery chemistry and engineering. Probably why many here shy away from diving and DIY packs. Look at the following chart. It is a random one put you can see the different C discharge rating and the range of time rated at C rates.

[Jim Blackwood]

I don't think whether or not the starter would take it is the issue here anyway. That fusible link business would be something fairly new. Any fusible link would be blown by heat which is a function of current times voltage so all you need is a way to limit those and such things do exist. So there certainly would be a way to apply 48 volts through such a device and avoid damaging the starter. How expensive that would be I can't say but it's certain it could be done.

The question was, why wouldn't the batteries be able to handle it? And that question hasn't been answered.

Jim

[freds]

There's a simpler solution!

Just keep your start batteries always topped off by using a solar charge controller that has it's solar input hooked to your 48V house battery pack.

All solar charge controllers know how to correctly charge a lead acid battery.

This works because most solar panels are between 36-72V when they are producing power. Doesn't have to be a high power solar charge controller.

Here's a inexpensive one with blue tooth that you can control from your phone.

https://www.amazon.com/Victron-SmartSolar-Charge-Controller-Bluetooth/dp/B075NQQRPD/ref=sr_1_1_sspa?crid=32QDJCHHGN14G&dchild=1&keywords=victron%2Bmppt%2B75%2F15&qid=1634487075&sprefix=victron%2Bmppt%2Caps%2C218&sr=8-1-spons&smid=A2VHGGOHXF24LJ&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEySldONjAwU1RVTFZDJmVuY3J5cHRlZElkPUEwNzQyNTAxMVNHQkpZSFU4TTZaSyZlbmNyeXB0ZWRBZElkPUEwMzk4NjQyUDRYMFBZWVlQRjRaJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ&th=1

[Jim Blackwood]

That's a good idea, but what if your start batteries just simply died? If starting from your house batteries was the only option, what would you do? Surely not punt.

Jim

[Dave5Cs]

Clifford said above.
You know the Delco 42 starter on your bus is a 900 amp 10 hp motor and they will draw those amps on a cold day I have seen higher, that is why lead batteries have cold cranking amps to turn that baby,The part I don't get is drawing a 100 amps from a 100 amp battery you only get maybe 30 seconds then drawing the same amps from a 100 amp battery would be like shorting one out I guess.

Don doesn't have a 42 he has a 39 like mine.