Sump pump updates - Battery Backup

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Minister of Fire
Oct 21, 2009
Holliston, MA USA
So in the previous post I detailed all the improvements I'm dong with the sump pump system. We have had rain bad enough to overwhelm the main pump, so even with a generator I wanted a backup.

I was looking for a battery backup that would:

- have as much or more capacity than a 1/3hp AC pump
- have at least an 8hr run time so if we lost power while at work I dont have to rush home to start the generator
- Recharge in a less than a day
- Be able to run on AC or DC so it can also kick in to help the AC pump or if the AC pump fails
- not cost thousands of $

I looked at a lot of options, including homebrewing my own system with a boat bilge pump and a big battery. In the end I settled on the Basement Watchdog Big dog system as it would do everything a homebrew would but cost less. And it has all kinds of automated failure monitoring options (batery, pump, etc test) built in.

Verdict - It works very well, and has good capacity. But there is one major flaw. They use a flooded deep cycle ( i think its aobut 140Ah) and their built in charging controller is just a dumb bulk charger. The battery is always powering the system and they monitor it and when it drops to 12.3 VDC under load it gets a 20amp top off charge. They rate te pump for AC operation because the pump load is 12 amps so the charger can feed it and still keep the battery full.

I can see why many users complain the batteries only last 2-3 years. Since they are only occasionally bulk charging the battery is often sitting in a partial discharge, and never gets a good equalization - so the batteries are probably sulfating. If they just spend the couple extra bucks and add a real 3 stage charger (bulk->absorption->float) and keep the battery on a 13v trickle all the time they would probably get 7-10 years life. I had a conversation with their tech support who tried to tell me that only maintenance free batteries need 3 stage charging so either they dont have a clue or are happy to sell more batteries.

Anyway, I will be disconnecting the battery once every couple months for an equalization charge on a good 12v charge controller. Anybody out there who has one of these systems I suggest you do the same.

IF I were to do it all again I would homebrew instead and setup a DC bilge pump (Rule, etc), with a big Group 4 or group 8 AGM battery and a GOOD lead acid charge control/power supply like the kind that off grid folks use (Something from Iota Engineering or Powermax for example). All of this might cost close to a grand and lack all the alarms, etc but would last a lot longer and probably more reliable.


I went for the one size smaller 'Watchdog' unit, (my max gpm is lower) and have a similar opinion about the battery charger. I 'like' the low battery water alarm feature....but I had it go off after ~9mos, and the battery took 4 cups of water! This is amazing to me (in a bad way).

I have played with the idea of wiring in a small float charger (I already own) maybe with a low R resistor (to keep it from bucking the Dog charger), or triggering its alarms. Based on your description, if I can float the battery, the Dog charger will never run (on standby). Or am I missing something? Have you tried this already??

EDIT: of course, my charger might be different from yours.
I think when their battery water alarm goes off the water level is probably almost down to the plates. I'm going to just look at it monthly. Note that I did a hydrometer test on this battery 'charged' and the cells read from 1.225 to 1.250. So this thing definitely needs to be equalized, and hope that's all.

I did some research and the cheapest chargers I can find with good reviews that have the option for a real equalization/desulfate cycle seem to be the noco genius line.

As far as paralleling a battery minder, I asked their tech and he told me it would damage the controller. I don't know if I have the skill to reverse engineer this thing to figure out if that's really true. So I'm going to rig up a quick disconnect to plug it into the external charter once a month without undoing everything.

One other thing I did was wire in a cigarette lighter socket, so in a short power outage we can use it to recharge phones,etc.
So I finally and time to disconnect the battery and let it charge on the noco genious charger. It ran for 5 hours! before it finished and topped off a bit over 13v. Higher than the BWD ever charged it to. NOw the hydrometer readings are varying from 1.240 to 1.250.

So it still needs an equalization but is in a bit better shape. And I dont think the BWD charges it much more than 85% full :(

Very disappointing :(
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