Second battery and isolator to keep batteries charged?

3251 Views 27 Replies 9 Participants Last post by uconduit, Oct 20, 2013

HackWork

Discussion Starter · Oct 19, 2013

I would like it if I could keep all my normally used batteries fully charged. That would be:

2 18V Dewalts
2 M12 Milwaukee
1 12V Makita
1 20V Dewalt

I was thinking about a system with a second battery and an isolator. I'd have an invertor on the second battery and the batteries charging from the inverter.

The question is how long would that second battery last for? I've read that the inverter alone, if left on overnight, could kill a battery. So with the batteries charging, would that kill the second battery completely?

When I leave the truck over the weekend, is the second battery going to die by Saturday night and then need to be fully recharged when I take the truck out Monday morning? If so, that won't work too well and would kill the second battery quick.

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uconduit

· #2 · Oct 19, 2013

What kind of battery were you thinking of using to recharge your other batteries? I'm assuming a lead-acid deep cycle, right, not just any old car battery. How long is your commute? You need to recharge the deep cycle too and the power for that comes from the alternator.

As for capacity, how many AHs do the chargers (combined) consume? does the candidate battery's AH capacity times 0.7 exceed the chargers' AH requirements? Will you run the engine long enough (as part of your day's travels) to recharge the deep cycle battery?

I'm certain that this could work out beautifully if it is executed properly though.

HackWork

Discussion Starter · #3 · Oct 19, 2013

uconduit said:
What kind of battery were you thinking of using to recharge your other batteries? I'm assuming a lead-acid deep cycle, right, not just any old car battery. How long is your commute? You need to recharge the deep cycle too and the power for that comes from the alternator.

The commute changes, depending on where the first job is. Yes, i would use a deep cycle battery.

As for capacity, how many AHs do the chargers (combined) consume? does the candidate battery's AH capacity times 0.7 exceed the chargers' AH requirements? Will you run the engine long enough (as part of your day's travels) to recharge the deep cycle battery?

I'm certain that this could work out beautifully if it is executed properly though.

I'm not sure of all of this. I just read that people killed their battery by forgetting to switch their inverter off so if the inverter alone could kill a battery overnight, an inverter with multiple chargers would probably do the same, or so I would assume.

So I was wondering if people have done this and what their experiences are.

Most of my jobs are short, the last thing I want to do is worry about charging batteries.

Dawizman

· #4 · Oct 19, 2013

My truck battery lasts no problem overnight running my 2000w inverter with 2 makita 18v lxt chargers running off if it. Over the weekend kills it though.

I have the inverter wired up through a timed relay though, so it will run 2hrs after the ignition turns off, and then the inverter shuts off. Charges my tool batteries up, and doesn't kill the truck battery.

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uconduit

· #5 · Oct 19, 2013

The equipment that you use has to have safeguards though to protect lead acid batteries from damaging under voltages. You can put a relay that isolates the deep cycle from the rest of the car's electrical system unless the vehicle is in the "on" position -- that would prevent the starting battery from being discharged. As for the inverter, I think that there are some that will shut off if the voltage is too low. But you need something, you don't want the battery from being discharged below a certain voltage. You also should determine whether recharging the lead-acid strains your alternator too much and if you should use a current limiting circuit to mitigate that.

For determining the AH requirements of the equipment you could research it or use a "kill-o-watt" or something like that and that will give you the information you need to size the inverter and battery.

Just off the top of my head, I'm thinking a 90 AH battery, 8 gauge from the starting battery to the deep cycle (with fuse near the starting battery and an isolating relay with coil energized when the key is at "on" somewhere in between). Probably a thick wire like 2 #4s between the deep cycle and inverter.

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FrunkSlammer

· #6 · Oct 19, 2013

Been thinking about this as well.. need a good solution to charge up batteries while on the go. Been using a powerbar with a retractable cord to just plug in. Prefer to automate the process and hide all cables away.

Timed relay for an inverter sounds like a clever idea!

BBQ

· #7 · Oct 19, 2013

Forget the inverter, that is just another layer of loss.

You would take truck 12 VDC, convert it to 120 VAC with a 'sine' wave that the chargers may not like only to convert the 120 VAC back to DC to charge the battery.

I suggest buying tool chargers that run on 12 VDC

http://www.dewalt.com/tools/chargers-dcb119.aspx

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HackWork

Discussion Starter · #8 · Oct 19, 2013

Dawizman said:
My truck battery lasts no problem overnight running my 2000w inverter with 2 makita 18v lxt chargers running off if it. Over the weekend kills it though.

I have the inverter wired up through a timed relay though, so it will run 2hrs after the ignition turns off, and then the inverter shuts off. Charges my tool batteries up, and doesn't kill the truck battery.

So that pretty much confirms it for me, thanks. I won't even bother.

My second choice is to just line the chargers up on a shelf and connect them to a power strip and then connect that power strip to an inlet on the side of the van. This way when I am at a job I could just run a cord from the customer's house to the inlet and charge all the batteries. I find myself in a situation to do this at least 2-3 times per week. That should be enough for the most part.

FrunkSlammer

· #9 · Oct 19, 2013

HackWork said:
This way when I am at a job I could just run a cord from the customer's house to the inlet and charge all the batteries. I find myself in a situation to do this at least 2-3 times per week. That should be enough for the most part.

Definitely works and definitely is cheap and definitely is a pain in the butt. Could do it that way for a few months, then change it if you get sick of it, like me.

I bought cordless tools so I could kick the extension cord habit. But I'm still using.. time to go clean and sober!

HackWork

Discussion Starter · #10 · Oct 19, 2013

The 12V charger idea is good, but expensive. I think it would be cheaper to buy a decent pure sine wave inverter then to buy all new 12V chargers. I have a lot of chargers right now, 6 or 7 Dewalt chargers alone.

What size pure sine wave inverter would I need for the 6 chargers I mentioned in the OP? I assume there will be a big inrush when they all start at the same time?

azgard

· #11 · Oct 19, 2013 (Edited)

HackWork said:
So that pretty much confirms it for me, thanks. I won't even bother.

My second choice is to just line the chargers up on a shelf and connect them to a power strip and then connect that power strip to an inlet on the side of the van. This way when I am at a job I could just run a cord from the customer's house to the inlet and charge all the batteries. I find myself in a situation to do this at least 2-3 times per week. That should be enough for the most part.

Depending on how elaborate and idiot proof you want your setup you could wire it up to an inverter with a relay setup for an ac inlet. Charge your tool's with the van started up and driving, shut's off when van is turned off or ac outlet hooked up. I did similar with my truck for a battery tender, 3kw inverter, and block heater. You can find most of what you would need at a marine store.

Edit: To address your question above, if you get a quality unit inrush is a non issue.
http://www.meanwell.com/search/ts-1000/default.htm

The above unit can be run at 150% for around 10 seconds before switching off and can handle 200% for half a second. Just figure out how much power your charger's draw and work from there.

LARMGUY

· #12 · Oct 20, 2013

Dawizman said:
My truck battery lasts no problem overnight running my 2000w inverter with 2 makita 18v lxt chargers running off if it. Over the weekend kills it though.

I have the inverter wired up through a timed relay though, so it will run 2hrs after the ignition turns off, and then the inverter shuts off. Charges my tool batteries up, and doesn't kill the truck battery.

I like it!

Jlarson

· #13 · Oct 20, 2013

Blue seas makes a nice isolator. I'll look for the part #.

uconduit

· #14 · Oct 20, 2013

A timed relay is inferior to a low voltage cutoff.

With a low-voltage cutoff the setpoint can be set to coincide to the battery's maximum safe depth of cycle. (for example the inverter turns off when the battery is at 11.8 volts which would be after supplying around ~80% of the batteries nameplate AH rating).

A relay is only concerned with time. It doesn't care if the deep cycle battery was discharged to 6 volts, and it doesn't care if you had an almost fully charged deep cycle and 8 dead dewalt batteries.

Check out WestMarine, it's mostly boat stuff though but they have far, far, far more sophisticated 12volt electrical equipment then the auto parts store. RV places are another option.

HackWork

Discussion Starter · #15 · Oct 20, 2013

Doing that won't work for me because everything I read says that leaving batteries in chargers when the chargers are unplugged or not getting power will discharge the batteries.

So the batteries would be charged for X amount of hours and then when the system shut off the batteries would be sitting in the chargers discharging.

I think it's better to forget about the second battery system and just get a pure sine wave inverter that could handle those 6 chargers and charge the batteries while driving. I believe all of my batteries charge within an hour so I could just charge them when I know I'll be driving that long.

I figure a 400watt PSW inverter should be good enough.

administr8tor

· #16 · Oct 20, 2013

HackWork said:
Doing that won't work for me because everything I read says that leaving batteries in chargers when the chargers are unplugged or not getting power will discharge the batteries.

So the batteries would be charged for X amount of hours and then when the system shut off the batteries would be sitting in the chargers discharging.

I think it's better to forget about the second battery system and just get a pure sine wave inverter that could handle those 6 chargers and charge the batteries while driving. I believe all of my batteries charge within an hour so I could just charge them when I know I'll be driving that long.

I figure a 400watt PSW inverter should be good enough.

400w won't handle 6 chargers

HackWork

Discussion Starter · #17 · Oct 20, 2013

administr8tor said:
400w won't handle 6 chargers

No? I haven't looked in a while but I thought the Dewalts were like 50W and the Milwaukee was even less.

administr8tor

· #18 · Oct 20, 2013 (Edited)

HackWork said:
No? I haven't looked in a while but I thought the Dewalts were like 50W and the Milwaukee was even less.

Don't know about dewalt I just checked my m12 draws 70w, makita 240w, hilti 125w, I have more but didn't unscrew from wall to check

FrunkSlammer

· #19 · Oct 20, 2013

Milwaukee m12 charger runs max at 90W I believe but the manual recommends a 100W or larger inverter.

Pretty sure you can keep Milwaukee and Makita batteries on the charger and they won't discharge the batteries.. at least not any amount that could be noticed.

administr8tor

· #20 · Oct 20, 2013

4

My setup with 600w can't run all at same time

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